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This is to certify that the

dissertation entitled

INFLUENCE OF BASAL LEAF REMOVAL AND CROPPING LEVEL

ON GROWTH, YIELD, COLD HARDINESS AND BUD FRUITFULNESS
IN SEYVAL GRAPEVINES (Vitis Sp.)

presented by

Maria Teresa Franco de Barros

has been accepted towards fulﬁllment
of the requirements for

Ph.D. degree in Horticulture

 

 

JJTW G. S. Howell

Major professor

Date February 8, 1993

 

MSU is an Afﬁrmative Action/Equal Opportunity Institution 042771

 

 

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MSU Is An Affirmative Action/Equal Opportunity Institution
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INFLUENCE OF BASAL LEAF REMOVAL AND CROPPING LEVEL
ON GROWTH, YIELD, COLD HARDINESS AND BUD FRUITFULNESS

IN SEYVAL GRAPEVINES (Vitis sp.)

 

By

Maria Teresa Franco de Barros

A DISSERTATION
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Horticulture

1993

 

 

 

ABSTRACT
INFLUENCE OF BASAL LEAF REMOVAL AND CROPPING LEVEL
ON GROWTH, YIELD, COLD HARDINESS AND BUD FRUITFULNESS
IN SEYVAL GRAPEVINES (Vitis Sp.)
By

Maria Teresa Franco de Barros

Basal leaf removal effects on growth and yield, and on the cold hardiness and
fruitfulness of the shoot region subjected to leaf removal, were studied in
differentially cropped own-rooted Seyval grapevines, whether young potted or mature
ﬁeld-grown vines.

Basal leaf removal had no signiﬁcant effect on vine growth, ﬂower-bud
differentiation and primary bud hardiness, in both potted and mature vines. Evidence
from potted vines suggested that an eventual compensation for leaf removal was
more effective following leaf removal at berry pea size than at veraison. The net C02
assimilation rate per unit of leaf area (A) was enhanced by leaf removal at pea size,
unlike at or shortly after veraison. Leaf removal had no signiﬁcant effect on dry
matter partitioning in potted vines, and little effect on starch and soluble
carbohydrate concentration in canes, roots, and trunk in the early fall, mid- and late
winter. In the few cases where a signiﬁcant effect was found, carbohydrate
concentration was higher in potted vines treated at pea size than in those treated at
veraison. The presence of fruits increased A, especially on potted vines. Cane and
trunk soluble carbohydrate per dry weight in the early fall (1.5 weeks after harvest)

were higher in fruiting (3C1) than in non-fruiting (0C1) potted vines, in

 

correspondence to fall cane hardiness, but there was no clear relationship between
hardiness and carbohydrate levels in the winter and early spring. Flower-bud
differentiation was lower on 3C1 than on 0C1 vines.

On mature vines, basal leaf removal improved the light microclimate in the
cluster region with no significant effect on yield and fruit composition. In 1990, when
canopies were denser, leaf removal at veraison reduced the percentage of rotten
clusters on the vines thinned to 1.5 clusters per node retained (1.5), but not on the
less vigorous, unthinned (NT) vines. Carbohydrate storage in 1989 was presumably
impaired due to an early leaf killing frost and, in mature vines, to a heavy 1989 crop.
Field cold injury was greater in the 1989/90 than in the 1990/91 dormant seasons,
as evidenced by a higher percentage of shootless nodes in 1990 than in 1991. This
percentage was not signiﬁcantly affected by leaf removal, and was lower on non-
fruiting (0) than on NT vines. In 1990 the number of clusters per primary shoot was
larger on 0 than on NT vines. Differences in yield, hardiness, cane maturity, and

primary bud fertility between 1.5 and NT vines were not signiﬁcant in any trial year.

To my parents who, from long ago, prepared the ground for this thesis, and my

ﬁance, the sunlight in its development. To my true friends.

iv

 

ACKNOWLEDGMENTS

I would like to express my sincere appreciation to my advisor, Professor G. Stanley
Howell, for his guidance and encouragement, his example as a person and a scientist, and
his invaluable friendship. I am also grateful to the members of my guidance committee,
Professors Donald Dickmann, James A. Flore, Kenneth L. Poff, and Kenneth Sink, who
were a source of scientiﬁc and moral support during my PhD program.

I would like to thank the Instituto Superior de Agronomia (ISA) and the Reitoria of
the Lisbon University of Technology (UTL) for granting me a leave at Michigan State
University (MSU). To Professors Pedro Amaro and Matos Silva, whose effort was crucial
for the obtention of that leave, as well as to Professor Carlos Portas and other Professors
who approved the continuation and completion of my PhD at MSU, I am deeply grateful.

This PhD program was ﬁnanced by a NATO scholarship granted by the Comissao
Permanente INVOTAN-JNICT. I gratefully acknowledge the support of this Comiss‘zio.

I am thankful to the colleagues in the Viticulture and Enology program, Dave Miller,
Charles Edson, Mike McLean and Russ Smithyman, as well as to Lynne Sage, Tom Dittmer,
Hannah Mathers and Halima Awale, for their assistance and friendship. I am also grateful
to Professor Charles Cress for kindly giving statistical advice.

Finally, I would like to thank my family and closest friends for their continued
encouragement. I especially thank Carlos Coelho for his help with the statistical analyses and

during the periods of most intense ﬁeld work, and for his invaluable moral support.

TABLE OF CONTENTS

LIST OF TABLES ............................................. ix
LIST OF FIGURES ............................................ xvi
INTRODUCTION .............................................. 1
LITERATURE REVIEW ........................................ 4
Radiation Microclimate and Grapevine Physiology ..................... 4
Introduction ................................................ 4
Light and Grapevine Photosynthesis ............................... 5
Radiation Microclimate and Grapevine Fruitfulness ................... 8
Radiation Microclimate and Cold Hardiness ....................... 12
Leaf Removal Effects on Vine Growth and Yield ..................... 17
Introduction ............................................... 17
Leaf Removal Effects on Vine Growth and Yield Components ......... 19
Leaf Removal Effects on Fruit Quality ........................... 21
Literature Cited ................................... ' ........... 23

CHAPTER 1. Inﬂuence of Basal Leaf Removal and Cropping Level on Leaf Gas
Exchange, Leaf Chlorophyll Content, Vegetative Growth, and Partitioning of Dry

Matter and Non-structural Carbohydrates in Seyval Grapevines ........... 36
Abstract ................................................... 37
Introduction ................................................. 38
Materials and Methods ........................................ 41
Results .................................................... 49
Discussion .................................................. 66
Conclusions ................................................. 76
Literature Cited .............................................. 77

vi

 

 

 

CHAPTER II. Inﬂuence of Basal Leaf Removal and Cropping Level on the Cold

Hardiness of Primary Bud and Cane Tissues of Seyval Grapevines ......... 83
Abstract ................................................... 84
Introduction ................................................. 85
Materials and Methods ........................................ 87
Results and Discussion ......................................... 94
Conclusions ................................................ 112
Literature Cited ............................................. 114

CHAPTER III. Inﬂuence of Basal Leaf Removal and Cropping Level on the Growth,
Canopy Microclimate, Yield and Fruit Composition of Seyval Grapevines . . . 119

Abstract .................................................. 120
Introduction ................................................ 121
Materials and Methods ....................................... 123
Results and Discussion ........................................ 128
Conclusions ................................................ 136
Literature Cited ............................................. 141

CHAPTER IV. Inﬂuence of Basal Leaf Removal and Cropping Level on the
Fruitfulness of Primary Buds of Seyval Grapevines. Localized and Positional

Treatment Effects ............................................ 145
Abstract .................................................. 146
Introduction ................................................ 147
Materials and Methods ....................................... 149
Results and Discussion ........................................ 155
Conclusions ................................................ 178
Literature Cited ............................................. 179

SUMMARY AND CONCLUSIONS .............................. 184

APPENDIX A. Inﬂuence of Basal Leaf Removal and Cropping Level on the
Stomatal Conductance, Transpiration Rate, and Water Use Efﬁciency at Basal,
Middle-shoot, and Apical Leaves of Seyval Grapevines ................. 188

vii

 

APPENDIX B. Inﬂuence of Vine Shading and Cropping Level on Leaf Gas
Exchange, Vegetative Growth, Dry Matter Accumulation, and Fruitfulness of Young

Potted Seyval Grapevines ....................................... 201
Abstract .................................................. 201
Introduction ................................................ 203
Materials and Methods ....................................... 204
Results and Discussion ........................................ 207
Conclusions ................................................ 231
Literature Cited ............................................. 232

viii

LIST OF TABLES

CHAPTERI

Table 1. Inﬂuence of leaf removal and cropping level on the net C02 assimilation

rate (A) of BAS, MID, and AP leaves of potted Seyval vines (HRC 1989 -
Experiment I). ............................................. 50

Table 2. Inﬂuence of leaf removal and cropping level on the net CO; assimilation

rate (A) of BAS, MID, and AP leaves of potted Seyval vines (HRC 1990 -
Experiment 11) .............................................. 51

Table 3. Inﬂuence of leaf removal and cropping level on the net CO, assimilation

rate (A) of BAS, MID, and AP leaves of mature ﬁeld Seyval vines (CHES
1990 - Experiment III). ....................................... 52

Table 4. Inﬂuence of leaf removal, cropping level and leaf position on the net C02

assimilation rate (A), stomatal conductance (g,), transpiration rate (E) and
water use efﬁciency (WUE) of leaves of potted Seyval grapevines at selected
vine phenophases (HRC 1989 - Experiment I) ..................... 54

Table 5. Inﬂuence of leaf removal, cropping level and leaf position on the net C02

assimilation rate (A), stomatal conductance (g,), transpiration rate (E) and
water use efﬁciency (WUE) of leaves of potted Seyval grapevines at selected
vine phenophases (HRC 1990 - Experiment II). .................... 55

Table 6. Inﬂuence of leaf removal, cropping level and leaf position on the net C02

Table

assimilation rate (A), stomatal conductance (g,), transpiration rate (E) and
water use efﬁciency (WUE) of leaves of mature ﬁeld Seyval grapevines at
selected vine phenophases (CHES 1990 - Experiment HI). ............ 56

7. Inﬂuence of leaf removal and cropping level on the total chlorophyll
content, chlorophyll a/b ratio, and speciﬁc leaf weight (SLW) of BAS, MID
and AP leaves of potted Seyval vines at veraison (August 24) and at harvest
(September 19) (HRC 1990 - Experiment II). ...................... 58

Table 8. Inﬂuence of leaf removal and cropping level on shoot growth parameters,

leaf area, and speciﬁc leaf weight of potted Seyval grapevines (HRC 1989 -
Experiment I). ............................................. 60

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Table 9. Inﬂuence of leaf removal and cropping level on shoot growth parameters,
leaf area, and speciﬁc leaf weight of potted Seyval grapevines (HRC 1990 -
Experiment 11). ............................................. 60

Table 10. Inﬂuence of leaf removal and cropping level in 1990 on the dry weight
partitioning of potted Seyval grapevines at the end of the season (September
30/90) (Experiment II). ...................................... 61

Table 11. Inﬂuence of leaf removal and cropping level in the 1990 season on the
dry weight of canes, trunk and roots of potted Seyval grapevines, on
average across partitioning dates in the fall and winter of 1990/91

(Experiment II). ............................................ 61

Table 12. Inﬂuence of leaf removal and cropping level on starch, soluble
carbohydrate, and total non-structural carbohydrate content per unit of dry
weight and per unit of volume of canes of potted Seyval grapevines (HRC
1990/91 - Experiment II) ..................................... 63

Table 13. Inﬂuence of leaf removal and cropping level on starch, soluble
carbohydrate, and total non-structural carbohydrate content per unit of dry
weight and per unit of volume of trunk of potted Seyval grapevines (HRC
1990/91 - Experiment II) ..................................... 64

Table 14. Inﬂuence of leaf removal and cropping level on starch, soluble
carbohydrate, and total non-structural carbohydrate content per unit of
dry weight of roots of potted Seyval grapevines (HRC 1990/91 - Experiment

II). ...................................................... 65

CHAPTER II

Tal>le 1. Inﬂuence of leaf removal and cropping level on cold hardiness (1‘50) of
primary bud and cane tissues of mature ﬁeld grown Seyval grapevines (CITES
1989/90 - Experiment I) ...................................... 96

Table 2. Inﬂuence of leaf removal and cropping level on cold hardiness (Tm) of
primary bud and cane tissues of mature ﬁeld grown Seyval grapevines (CHES,
1990/91 - Experiment I) ..................................... 97

Table 3. Inﬂuence of leaf removal and cropping level on the cold hardiness (Tm) of
primary bud and cane tissues of 2 year—old potted Seyval grapevines (HRC
1990/91 - Experiment 11). .................................... 104

 

Table 4. Inﬂuence of leaf removal and cropping level during the 1989 and 1990

seasons on the number of canes per vine with 5 or more mature nodes before
pruning at the end of the following winter (April 13/90 and April 1/91), and
on the within vine distribution of canes on April 1/91 by diameter and
maturity eategories related to cold resistance (Experiment I) .......... 109

Table 5. Number of nodes retained on mature ﬁeld grown Seyval grapevines prior

Table

to treatment imposition (1989), and inﬂuence of leaf removal and cropping
level in the 1989 and 1990 seasons on the number of nodes retained at
pruning and on the percentage of shootless nodes in the seasons following
treatment application (Experiment I) ............................ 110

CHAPTER III

1. Vine size and number of nodes retained per vine prior to treatment
imposition and inﬂuence of leaf removal and cropping level on the yield, fruit
composition and rot levels of mature ﬁeld Seyval grapevines in 1989 (Year 1).
Harvest date: September 27/89. ............................... 130

Table 2. Inﬂuence of leaf removal and cropping level on the vine size and number

of nodes retained per vine at pruning after the ﬁrst treatment season and on
the yield, fruit composition and rot levels of mature ﬁeld Seyval grapevines
in 1990 (Year 2). Harvest date: September 25/90. .................. 131

Table 3. Inﬂuence of leaf removal and cropping level treatments in 1989 (Year 1)

and 1990 (Year 2) on the vine size and number of nodes retained per vine in
1991 and 1992, and in the yield, fruit composition and rot levels of mature
ﬁeld Seyval grapevines in 1991 (Year-3), when no differential treatments were
applied. Harvest date: September 6/91. ......................... 133

Table 4. Inﬂuence of 1989 (Year 1) and 1990 (Year 2) leaf removal and cropping

Table

Table

level treatments on shoot growth parameters of mature ﬁeld Seyval vines at
the end of the treatment seasons and of the 1991 (Year 3) season, in which
no differential treatments were applied. .......................... 134

5 . Inﬂuence of leaf removal and cropping level on canopy parameters of
mature Seyval grapevines on September 26/89, the day before harvest in the
ﬁrst treatment season, as evaluated by point quadrat analysis. ......... 137

6. Inﬂuence of leaf removal and cropping level on the percentage of
photosynthetic photon ﬂux (PPF) reaching the cluster region of the canopy of
mature Seyval grapevines on September 17/ 89, 1.5 weeks before harvest in the
ﬁrst treatment season. ...................................... 137

xi

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Table 7. Inﬂuence of leaf removal and cropping level on canopy parameters of

Table

mature Seyval grapevines during 1990, the second treatment season, as
evaluated by point quadrat analysis. ............................ 138

8. Inﬂuence of leaf removal and cropping level on the percentage of

photosynthetic photon ﬂux (PPF) reaching the cluster region of the canopy of
mature Seyval grapevines during 1990, the second treatment season. . . . .139

CHAPTER IV

Table 1. Inﬂuence of 1989 (Year 1) leaf removal and cropping level treatments on

the fruitfulness of potted Seyval grapevines in 1990 (Year 2), evaluated on a
yin; basis (Experiment I). .................................... 157

Table 2. Inﬂuence of 1990 (Year 1) leaf removal and cropping level treatments on

the fruitfulness and yield components of potted Seyval grapevines in 1991
(Year 2), evaluated on a yine basis (Experiment 11). ................ 158

Table 3. Inﬂuence of 1989 (Year 1) and 1990 (Year 2) leaf removal and cropping

level treatments on the percentage of fruitful primary shoots and on the
number of clusters per shoot in mature ﬁeld Seyval grapevines in 1990 (Year
2) and 1991 (Year 3), evaluated on a yin; basis (Experiment III). ...... 160

Table 4. Signiﬁcance of the effects of 1989 (Year 1) leaf removal (DEF), cropping

level (CROP), bud position (BP), defoliation at a speciﬁc node (BDEF),
presence of a cluster at a speciﬁc node (PCL), and interactions, on the
fruitfulness and yield components of potted Seyval grapevines in 1990 (Year
2), evaluated on a bug basis (Experiment I). Mean values for DEF, CROP,
and BP levels relative to these analyses are presented in Table 5 ....... 162

Table 5. Inﬂuence of bud position and 1989 (Year 1) leaf removal and cropping level

treatments on the fruitfulness of potted Seyval grapevines in 1990 (Year 2),
evaluated on a bud basis (Experiment I) ......................... 163

Table 6. Signiﬁcance of the effects of 1990 (Year 1) leaf removal (DEF), cropping

level (CROP), bud position (BP), defoliation at a speciﬁc node (BDEF),
presence of a cluster at a speciﬁc node (PCL), and interactions, on the
fruitfulness and yield components of potted Seyval grapevines in 1991 (Year
2), evaluated on a but basis (Experiment 11). Mean values for DEF, CROP,
and BP levels relative to these analyses are presented in Table 7 ....... 164

xii

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Table 7. Inﬂuence of bud position and 1990 (Year 1) leaf removal and cropping level
treatments on the fruitfulness and yield components of potted Seyval
grapevines in 1991 (Year 2), evaluated on a bud basis (Experiment 11). . .166

Table 8. Signiﬁcance of the effects of 1989 (Year 1) and 1990(Year 2) leaf removal
(DEF), cropping level (CROP), bud position (BP), defoliation at a speciﬁc
node (BDEF), presence of a cluster at a speciﬁc node (PCL), and interactions,
on the number of clusters per primary shoot of mature ﬁeld Seyval grapevines
in 1990 (Year 2) and in 1991 (Year 3), evaluated on a bud basis (Experiment
III). Mean values for DEF, CROP, and BP levels relative to these analyses are
presented in Table 9 ........................................ 170

Table 9. Inﬂuence of bud position, and 1989 (Year 1) and 1990 (Year 2) leaf
removal and cropping level treatments on the number of clusters per primary
shoot of mature Seyval grapevines in 1990 (Year 2) and 1991 (Year 3),
evaluated on a bug basis (Experiment HI). ....................... 171

APPENDIX A

Table 1. Inﬂuence of leaf removal and cropping level on the stomatal conductance
(g,) of BAS, MID, and AP leaves of potted Seyval vines (HRC 1989 -
Experiment I). ............................................ 192

Table 2. Inﬂuence of leaf removal and cropping level on the transpiration rate (E)
of BAS, MID, and AP leaves of potted Seyval vines (HRC 1989 - Experiment
I) ....................................................... 193

Table 3. Inﬂuence of leaf removal and cropping level on the water use efﬁciency
(WUE) of BAS, MID and AP leaves of potted Seyval vines (HRC 1989 -
Experiment I) ............................................. 194

Table 4. Inﬂuence of leaf removal and cropping level on the stomatal conductance
(g.) of BAS, MID, and AP leaves of potted Seyval vines (HRC 1990 -
Experiment II). ............................................ 195

Table 5. Inﬂuence of leaf removal and cropping level on the transpiration rate (E)
of BAS, MID, and AP leaves of potted Seyval vines (HRC 1990 - Experiment
II). ..................................................... 196

Table 6. Inﬂuence of leaf removal and cropping level on the water use efﬁciency
(WUE) of BAS, MID, and AP leaves of potted Seyval vines (HRC 1990 -
Experiment 11). ............................................ 197

xiii

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Table 7. Inﬂuence of leaf removal and cropping level on the stomatal conductance
(g,) of BAS, MID, and AP leaves of mature ﬁeld Seyval vines (CHES 1990 -
Experiment III). ........................................... 198

Table 8. Inﬂuence of leaf removal and cropping level on the transpiration rate (E)
of BAS, MID, and AP leaves of mature ﬁeld Seyval vines (CHES 1990 -
Experiment III). ........................................... 199

Table 9. Inﬂuence of leaf removal and cropping level on the water use efﬁciency
(WUE) of BAS, MID, and AP leaves of mature ﬁeld Seyval vines (CHES
1990 - Experiment III). ...................................... 200

APPENDIX B

Table 1. Inﬂuence of shading and cropping level on the net C02 assimilation rate (A)
of BAS, MID, and AP leaves of potted Seyval vines (HRC 1990) ....... 208

Table 2. Inﬂuence of shading and cropping level on the stomatal conductance (g,) of
BAS, MID, and AP leaves of potted Seyval vines (HRC 1990) ......... 209

Table 3. Inﬂuence of shading and cropping level on the transpiration rate (E) of
BAS, MID, and AP leaves of potted Seyval vines (HRC 1990). ........ 210

Table 4. Inﬂuence of shading and cropping level on the water use efﬁciency (WU E)
of BAS, MID, and AP leaves of potted Seyval vines (HRC 1990) ....... 211

Table 5. Inﬂuence of shading, cropping level and leaf position on the net CO2
assimilation rate (A), stomatal conductance (g,), transpiration rate (E) and
water use efﬁciency (WUE) of leaves of potted Seyval grapevines at selected
vine phenophases (HRC 1990) ................................. 212

Table 6. Inﬂuence of shading and cropping level on the total chlorophyll content,
chlorophyll a/b ratio, and speciﬁc leaf weight (SLW) of BAS, MID and AP
leaves of potted Seyval vines at veraison (Aug. 24) and at harvest (Sept. 19)
(HRC 1990) .............................................. 217

Table 7. Inﬂuence of shading and cropping level on shoot growth parameters, leaf
area, and speciﬁc leaf weight of potted Seyval grapevines (HRC 1990). . .219

Table 8. Inﬂuence of shading and cropping level in 1990 on the dry weight

partitioning of potted Seyval grapevines at the end of the season (September
30/90). .................................................. 221

xiv

 

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Table 9. Inﬂuence of shading and cropping level during the 1990 season on the dry
weight of canes, trunk and roots of potted Seyval grapevines, on average
across partitioning dates in the fall and winter of 1990/91. ........... 221

Table 10. Inﬂuence of 1990 (Year 1) shading and cropping level treatments on the
fruitfulness and yield components of potted Seyval grapevines in 1991 (Year
2), evaluated on a yin: basis. ................................. 223

Table 11. Signiﬁcance of the effects of 1990 (Year 1) shading (SH), cropping level
(CROP), bud position (BP), presence of a cluster at a speciﬁc node (PCL),
and interactions, on the fruitfulness and yield components of potted Seyval
grapevines in 1991 (Year 2), evaluated on a bad basis .Mean values for
SH, CROP, and BP levels relative to these analyses are presented in Table
12 ...................................................... 225

Table 12. Inﬂuence of bud position and 1990 (Year 1) shading and cropping level
treatments on the fruitfulness and yield components of potted Seyval
grapevines in 1991 (Year 2), evaluated on a bad basis. .............. 227

XV

   

LIST OF FIGURES

CHAPTERII

Figure 1. Maximum-minimum temperature proﬁle for the 1989/90 dormant season
at the site of Experiment I (Clarksville) and the cold hardiness (Tm) of
primary bud and cane tissues per cropping level x leaf removal treatment
combination on mature Seyval grapevines in the late fall, mid-winter and early
spring of 1989/90 (sampling dates indicated by arrows in the upper graph).
Means per treatment level are presented in Table 1 ................. 98

Figure 2. Maximum-minimum temperature proﬁle for the 1990/91 dormant season
at the site of Experiment I (Clarksville) and the cold hardiness (Tm) of
primary bud and cane tissues per cropping level x leaf removal treatment
combination on mature Seyval grapevines in the late fall, mid-winter and early
spring of 1990/91 (sampling dates indicated by arrows in the upper graph).
Means per treatment level are presented in Table 2 ................ 100

xvi

 

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INTRODUCTION

Photosynthesis is the basis for the vegetative and reproductive processes in
plants. However, not only is carbohydrate synthesis important, but so too is
earbohydrate partitioning into the different plant organs.

During most of the vegetative season, the processes of fructiﬁcation, growth,
and ﬂoral differentiation for the next crop occur simultaneously in grapevines,
thereby competing for carbohydrates. By the end of the season, enough carbohydrates
should be available for accumulation in storage organs. An adequate accumulation
of reserves assumes a special meaning in cold regions given the important role that
carbohydrates are considered to play in the development and maintenance of cold
hardiness (Howell, 1988).

Because the leaves are the main photosynthetic organs, leaf area and
carbohydrate availability are intimately related. Leaf removal, as a means to improve
the microclimate in the cluster zone, can be a practice of interest mainly for
excessively vigorous grapevines because it may reduce bunch rot and enhance
ripening (Wolf et a1., 1986;1(oblet, 1987,1988;Kliewer and Bledsoe, 1987; Bledsoe
it 2.1., 1988; Smith 91 al., 1988; English at al., 1989). However, leaf removal can also
result in severe carbohydrate depletion, with serious consequences to the grapevines.

Hence, it is no wonder that conﬂicting reports exist on the effects of leaf removal on
vine growth and on yield parameters and quality. Even though leaf removal is an

1

‘_

2

existing management practice with proven economic beneﬁts on high value cultivars
(Smith at al., 1988), it is still uncertain ‘how,when, where, and how many leaves must
be removed’ (Hunter and Visser, 1990).

The research team led by Dr. G. S. Howell at Michigan State University has
been a pioneer in studying the impact of defoliation and other cultural practices on
the cold hardiness of grapevines, beyond the effects on growth and productivity

parameters. The defoliation studies conducted have involved the complete defoliation

 

of the vines (Stergios and Howell, 1977; Howell at al. , 1978) and either complete
defoliation or the defoliation of alternate vine portions (cordon, shoots, leaves)
(Mansﬁeld and Howell, 1981). In the present study, leaves were removed from the
cluster region, hence the basal portion of the shoots. Basal leaf removal implies that
the buds axillary to the leaves removed are likely to be retained at pruning and give
rise to the new shoot growth and crop in the following season. Therefore, the
viability of these buds (which in cold climates is largely conditioned by their cold
hardiness), as well as their fruitfulness, have an important cultural signiﬁcance.
The main source of photosynthate for a bud seems to be the leaf subtending
it (Hale and Weaver, 1962; Smart at al. , 1982b). Hence, leaf removal may have a
negative effect on the carbohydrate status of the buds axillary to the leaves removed
and, consequently, on their fruitfulness and cold resistance. On the other hand,
several authors suggested that grapevines have compensatory mechanisms for losses
in leaf area, which may result in increased photosynthetic activity of the remaining
fOll'age and increased leaf area on lateral shoots (Buttrose, 1966; Kliewer, 1970;

[ﬂiewer and Fuller, 1973; Hoﬁcker, 1978; Hunter and Visser, l988a,b; Koblet, 1988;

 

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3
Reynolds and Wardle, 1989a; Candolﬁ-Vasconcelos, 1990; Hunter and Visser, 1990).

Moreover, an alteration in the carbohydrate transport was reported in response to
leaf removal (Quilan and Weaver, 1970). These responses might attenuate, to some
extent, a localized earbohydrate depletion due to leaf removal.

The objectives of this study were: 1) to investigate whether photosynthesis can
be enhanced by removal of a few basal leaves on vines under different cropping
regimes; 2) to assess the basal leaf removal and cropping effects on dry matter
partitioning and on non-structural carbohydrate levels namely in the restricted shoot
region subjected to leaf removal; 3) to evaluate the treatment effects on the cold
hardiness and fruitfulness of the treated shoot region and their probable relationship
with 1) and 2); 4) to evaluate the vine growth and yield responses to basal leaf
removal and cropping level, and potential limitations of basal leaf removal derived
from the localized effects analyzed in 3). The study was conducted on Seyval
grapevines (Seyve-Villard 5-276), one of the most important white wine cultivars in
the Eastern United States (Reynolds at al., 1985; Kaps and Cahoon, 1989). This
French-American hybrid has a propensity to overcrop and produces large and
compact clusters, extremely susceptible to bunch rot m cinema Pers). Leaf
removal in the cluster region could be helpful in reducing this problem, if no adverse

effects, namely on cold hardiness, are found to result from this practice.

LITERATURE REVIEW

Radiation Microclimate and Grapevine Physiology

Mutation

Radiation microclimate is known to inﬂuence several physiological processes
in plants and in the grapevine in particular. The effects of radiation on plant
physiology are mainly exerted through the supply of energy for photosynthesis, the
supply of speciﬁc wavebands that regulate photomorphogenesis, and tissue heating
(Kliewer, 1982).

Light is the region of the electromagnetic radiation spectrum to which the
human vision is sensitive (Smart, 1987). However, for simpliﬁcation, the term ‘light’
will refer in this review to Photosynthetically Active Radiation (PAR, 400-700 nm
waveband). The ﬂux of PAR will be termed Photosynthetic Photon Flux (PPF) and
expressed as umol of photons m'zs".

Light is the climatic component most affected by canopy density (Smart, 1985).
In the interior of dense canopies, PPF is reduced to less than 1% of the above
canopy level. Moreover, in dense canopies, the ratio 660 nm/730 nm radiation
(red/far red) may decrease to less than 10% of the ambient (Smart, 1982; Smart et
a1. , 1982a). This qualitative change in radiation has important physiological
implieations because it affects the phytochrome equilibrium and, hence, the processes

4

 

 

 

 

 

 

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5
controlled by this pigment (Smart, 1987).

Shaded grapevine canopies exhibit an inferior development of shoots, buds,
leaves and berries (Shaulis and Smart, 1974; Kliewer, 1982). In the interior of dense
canopies, a reduced photosynthetic rate (Kriedemann, 1968; Kriedemann and Smart,
1971; Smart, 1974; Kliewer, 1982) and early leaf abscision (Shaulis and Smart, 1974;
Kliewer, 1982) are observed. Shoots are affected in their carbohydrate content,
periderm formation and vascular development (Shaulis and Smart, 1974; Kliewer,
1982). Fruitfulness (Shaulis at al., 1966; May it al., 1976; Shaulis and May, 1971;
Shaulis and Smart, 1974) and cold hardiness (Shaulis and Smart, 1974; Stergios and
Howell, 1977; Howell et a1., 1978; Kliewer, 1982; Wolpert and Howell, 1985a;
Howell, 1988) are decreased. Berry growth and composition are markedly impaired
(Shaulis and Smart, 1974;K1iewer, 1982; Reynolds 91 al., 1985; Smart, 1987; Kliewer
at 31., 1988; Morrison, 1988; Archer and Strauss, 1989; Morrison and Nobel, 1990).

Smart (1987) stressed that a difﬁculty exists in determining the extent to which
the radiation effects on fruit composition might be phytochrome mediated, as
opposed to photosynthetic or thermal effects. The same might apply to the radiation
effects on fruitfulness and cold hardiness, even though in grapevines the involvement
of phytochrome in these processes is not clear, as can be inferred from further

sections.

I'l 15 '21 l'

The light response curve of photosynthesis in grapevine leaves was shown to

fOHOW a rectangular hyperbole (Kriedemann, 1968; Kriedemann and Smart, 1971).

 

 

 

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In a study with cv. Gewurztraminer, Smart (1985) found a light compensation point
of 15-20 pmol m‘zs“, i.e.,less than 1% of full sunlight. Light saturation occurred at
about 700 umol m‘zs", with a maximum photosynthetic rate of 0.55 mg C02 m'zs“.
Grapevines grown under reduced illumination show a lower light compensation point
and lower saturation values than those developed under full sunlight (Kriedemann,
1968). levels of PPF above saturation may result in decreased photosynthetic rate
due to photoinhibition (Powles, 1984). 1
A wide range of values for the light compensation point, the light saturation
levels, and the maximum photosynthetic rate in grapevine leaves are found in the
literature, as reviewed by Carbonneau (1976), Koblet (1985), and Chaves (1986). The
differences encountered might be due not only to the cultivar under study but also
to the conditions of measurement. Indeed, temperature (Buttrose and Hale, 1971;
Kriedemann, 1968, 1977) and vine water status (Kriedemann and Smart, 1971; Smart,
1974; Kriedemann, 1977) are important factors in determining the photosynthetic
response. Other factors known to inﬂuence grapevine photosynthesis and that might
also explain the differences found in the photosynthetic responses to light include leaf
age (Kriedemann, 1968,1977;Kriedemann at Q, 1970), time of the day (Kriedemann
and Smart, 1971; Loveys, 1984; Loveys and During, 1984; Chaves, 1986; Chaves at
al., 1987; Downton at al., 1987), seasonal trends (Kriedemann, 1977; Pandey and
Farmahan, 1977; Scholeﬁeld et a1. ,1982;Koblet, 1988), and source/ sink relationships
(Humphries and Theme, 1964; Kriedemann and Lenz, 1972; Hofacker, 1978; Herold,
1980; Chaves, 1984; Hunter and Visser, 1988a,b; Kaps and Cahoon, 1989; Candolﬁ-

Vasconcelos, 1990).

 

7

The photosynthetic rates measured on individual leaves and those of the
whole vine are not necessarily related. In a study with potted Seyval grapevines,
Edson (1991) found no correlation between single leaf and whole vine
photosynthesis. This was attributed, among other reasons, to the fact that the global
plant photosynthesis results from the activity of a continuum of leaves of different
physiologieal ages, some of them assimilating under suboptimal conditions. By

contrast, the leaf angle to the sun, for instance, was optimized when measuring

 

photosynthesis at individual leaves (Edson, 1991).

On standard canopies, the preferred leaf orientation is more vertical than
horizontal (Smart, 1985). In Concord canopies Smart at al. (1982a) observed that
leaves preferably formed an angle of about 45°C to the horizon. As quoted by
Kriedemann and Smart (1971), the photosynthesis of the whole canopy is higher
when the outer leaves are more or less pendulous, allowing for a greater penetration
of direct sunlight.

Canopy management practices to maximize the interception of PAR in
grapevine canopies have been intensively investigated since the pioneering studies of
Dr. N. Shaulis in New York State (Smart at al., 1990). Canopy division and reduced
vine spacing were both shown to enhance light interception by increasing canopy
length per hectare (Shaulis at al, 1966; Shaulis and Smart, 1974; Carbonneau at a,
1981; Smart, 1985; Smart et al.,1990).

Close, high, vertical, and north-south oriented canopy walls allow for maximal
light interception. However, they should not be so close and high as to result in a

Shaded canopy base (Smart, 1985; Smart :1 al., 1990). Divided canopy systems of

rating
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training to improve the radiation microclimate include Geneva Double Curtain
(GDC) (Shaulis :1 al.,1966), Lyre (Carbonneau at al., 1981; Carbonneau, 1985), and
Te Kauwhata Two Tier (Smart, 1985).

Additional practices to improve the radiation microclimate in canopies, such
as vigor control, shoot positioning, leaf removal, and shoot trimming are discussed

by Kliewer (1982), Koblet (1988), and Smart :1 a1. (1990).

vin F i In
Buttrose (1974) presented a review on the climatic factors inﬂuencing
fruitfulness in grapevines. Fruitfulness of grapevine buds is strongly promoted by
temperature (an optimum range of 30-35°C being reported by Buttrose, 1969a), and
light (May and Antcliff, 1963; May, 1965; Shaulis et al., 1966; Buttrose, 1970, 1974;
Shaulis and May, 1971; Shaulis and Smart, 1974; Kliewer, 1982; Smart gt a” 1982b;
Morgan et a1., 1985). These factors can readily be assumed to interact in inﬂuencing
ﬂowering and fruiting under ﬁeld conditions.
May and Antcliff (1963) found that light intensity was important for ﬂower
bud formation in ‘Sultana’ grapevines and that shading inhibited fruitfulness when
applied during the period of inﬂorescence initiation. The improvement of the light
conditions in grapevine canopies may not only increase the fertility of the buds but
also the number of buds that originate shoots (Kliewer, 1982). Moreover, light, along
With temperature, is a major factor in inﬂuencing fruit set in grapevines (Roubelakis
and Kliewer, 1976).

The importance of light exposure for ﬂower bud formation and fruiting of fruit

 

 

 

9
trees is also well documented (Jackson and Sweet, 1972; Cain, 1973; Jackson, 1980;

Flore, 1981). However, neither in grapevines (Kliewer, 1982) nor in fruit trees
(Iakso, 1986) is the mechanism for this light effect entirely elucidated.

The hypothesis that the carbohydrate-nitrogen ratio was important for ﬂower
initiation in perennial fruit crops was already largely abandoned in the early 60’s,
even though carbohydrates were still considered essential for satisfactory ﬂowering
(May, 1965). The view that carbohydrates may play an important role in bud
differentiation still exists, at least in the case of the grapevine (Shaulis and May,
1971; Buttrose, 1974; Winkler at al., 1974; Bains et a1., 1981; Smart at al., 1982b;
Morgan at al., 1985), even though there is insufﬁcient evidence to suggest that bud
development is limited by nutritional as opposed to hormonal regulation (Smart :1
a1. , 1982b). In grapevines, cytokinins have been shown to promote the growth of
inﬂorescences (Mullins, 1967) and ﬂowers (Pool, 1975), the development of pistils
by staminate ﬂowers (Negi and Olmo, 1972), and the production of inﬂorescences
and ﬂowers in tendrils (Srinivasan and Mullins, 1978). Cytokinins have also been
implicated in the ﬂowering of apple trees (Hoad and Abbott, 1986) and other species
(Leopold and Kriedemann, 1975). Jackson and Sweet (1972) agreed with the
argument of Evans (1969) that the differentiation of a ﬂower, as of any other organ,
is dependent on the spatial and temporal interaction of endogenous hormones and
assimilates, rather than on a speciﬁc ﬂoral stimulus. This argument seems suitable
for ﬂower-bud initiation in woody plants (Jackson and Sweet, 1972).

The yield of grapevines is determined, among other factors, by the

development of the buds and their inﬂorescence primordia, and the accumulation of

p

 

10
photosynthate in the season preceding harvest (Shaulis and May, 1971; Morgan at 21.,

1985). Smart et al. (1982b) observed a positive correlation between the illuminance
of the leaf subtending a bud (evaluated by hemispherical photography) and the
productivity of the shoot(s) arising from that bud in the following year. These authors
suggested that a reason for this relationship might be that the leaf subtending the
bud is the main source of photosynthate for that bud.

It is still under debate, though, whether the fertility of a bud is increased due
to improved light conditions of its subtending leaf or to improved exposure of the
bud itself (Kliewer, 1982). May (1965) found that in cv. Sultana shading of buds
without shading of leaves reduced inﬂorescence formation. The leaf primordia inside
shaded buds were etiolated, which supported a previous hypothesis (May, 1964) that
initiation and development of inﬂorescences was determined, at least in part, by the
growth of the vegetative components of the mixed grapevine bud. May (1965),
however, did not rule out the idea of an external carbohydrate supply. Indeed,
shading of buds might have reduced their import of assimilates at the time when
inﬂorescence initiation was to occur, and thereby result in the lack of assimilates at
the apex region where initiation should take place (May, 1965).

Roubelakis and Kliewer (1976) studied the inﬂuence of light/ temperature
regimes on the fruit set of ﬁve grapevine cultivars, and suggested that an insufﬁcient
availability of assimilates was responsible for the failure of fruit set observed at
reduced light/temperature levels. Under these conditions, neither the cytokinin 6-
benzyladenine nor CCC were effective in promoting fruit set. Both growth regulators

have, however, been widely reported to enhance fruit set under favorable climatic

11

conditions, the former supposedly by attracting assimilates to the cluster and the
latter by diverting assimilates from shoot tips to developing ovaries (Roubelakis and
Kliewer, 1976).

Photoperiod does not inﬂuence ﬂowering in many fruit and forest trees
(Jackson and Sweet, 1972). Grapevine buds tend to be more fruitful when developed
under long days, but the operative factor may be the extra production of
photosynthates associated with long days (Buttrose, 1974). Buttrose (1969b) could not
ﬁnd an effect of photoperiod on grapevine fruitfulness. However, contradictory
results have been obtained in studies under controlled vs. natural environments
(Smart at 3.1., 1982b). Varietal differences may also inﬂuence the response of
fruitfulness to day length (Buttrose, 1969b).

The role of radiation quality in grapevine fruitfulness has not been
conclusively determined. May (1965) observed that the shading of buds with different
materials reduced the percentage of fruitful buds but this effect seemed to be related
to a reduction in radiation intensity rather than to a change in quality. This study is
sometimes quoted to illustrate that the quality of radiation is not important for
grapevine fruitfulness (Morgan et al.,1985). However, Morgan at al. (1985), reported
that both PPF and radiation quality inﬂuenced the fruitfulness of cv. Muller Thurgau,
but the red/far red ratio had a minor effect, in contrast with PPF. There was a
consistent trend for reduction in the number of clusters per shoot in the treatments
with low red/ far red ratio relatively to the treatments with a high ratio. Nevertheless,
the number of ﬂowers per cluster was not related to the red/ far red ratio, neither

was the fruitfulness index (number of ﬂowers/total buds) (Morgan 91 a1. , 1985).

12

Given the diversity of the results obtained, the involvement of phytochrome
in the grapevine fruitfulness needs to be further investigated (Kliewer, 1982; Smart

:1 al., 1982b).

Light and temperature are the main environmental effects controlling the
development of cold hardiness in plants (Levitt, 1980). Photoperiod is also an
important factor in the cold acclimation of some species (van Huystee at al. , 1967;
Howell and Weiser, 1970; Williams at 31., 1972).

The major need for light seems to be due to a need for photosynthates (Levitt,
1980). A number of studies involving a wide range of species with different light
cycles have supported the view that qualitative and quantitative changes in
carbohydrates may be important for the development and maintenance of cold
hardiness (Levitt, 1956, 1980). Changes in other cellular substances such as lipids
(Ketchie, 1966; Kuiper, 1970; Uemura and Yoshida, 1984; Yoshida and Uemura,
1984; Lynch and Steponkus, 1987), nucleic acids (Li and Weiser, 1967; Brown and
Sasaki, 1972; Gusta and Weiser, 1972; Guy 91 al, 1985; Mohapatra et al., 1987;
Gilmour at al., 1988; Hajela at al., 1990), proteins (Siminovitch and Briggs, 1949,
1953; Li and Weiser, 1967; Brown and Sasaki, 1972; Gusta and Weiser, 1972;
Yoshida and Uemura, 1984; Guy e_t al., 1985; Robertson :1 al.,1987;Mohapatra et
al., 1988; Guy, 1990), and growth regulators, namely ABA (Irving, 1969; Perry and
Hellmers, 1973; Daie and Campbell, 1981; Chen et al., 1983; Bray, 1989) have also

been investigated for their possible involvement in cold acclimation. These metabolic

13

changes are necessarily related to alterations in enzyme activity or in gene expression
(Bray, 1989). Levitt (1980) and Guy (1990) reviewed the physiological role that the
metabolic and physiological changes might play in the hardening processes.

In mulberry (Sakai, 1960), peach (Layne and Ward, 197 8), red—osier dogwood
(Chen and Li, 1977), apple (Raese et al., 1978), and several other species (Ievitt,
1956, 1980), a close relationship was found between the degree of hardiness and the
levels of certain sugars or sugar derivatives. Sugars usually increase in fall as plants
harden and decrease in spring with dehardening (Siminovitch at al., 1953; Levitt,
1956).

Even though carbohydrate conversions (namely starch-sucrose) are widely
known to be related with hardening and dehardening, the enzymology of
carbohydrate metabolism during cold acclimation is not yet elucidated (Guy, 1990).

The nature of the carbohydrates accumulated during cold hardening and of
the prevalent earbohydrate has been found to vary from species to species and among
different climates (Siminovitch et a1. , 1953). In grapevines, a conversion of starch to
sugars (sucrose and reducing sugars) during the fall and early to mid-winter was
reported by Richey and Bowers (1924), Schrader ( 1924), Winkler and Williams
(1945), and Kliewer (1967), but its relationship with cold hardiness was not
investigated in these studies. Recently, though, a positive correlation was noticed
between sugar levels and cold hardiness in cv. Cabernet Sauvignon (Wample at al. ,
1988).

In contrast with the above ﬁndings, Steponkus and Lanphear (1968) found no

parallelism between sugar content and hardiness levels in English ivy. A similar lack

14

of correlation was observed in other studies (Levitt, 1980). Despite these results,
Steponkus and Lanphear (1968) did not deny to carbohydrates a role in the cold
acclimation processes. Rather, they suggested that acclimation does not result merely
from an accumulation of sugars and that a precise parallelism between the two would
only be expected if sugar content were the rate limiting step in acclimation.

Some possible roles of carbohydrates in hardiness have been proposed. A
suggestion by Levitt (1956) was that sugars would have an osmotic role in hardiness.
Accumulation of sugars in the vacuole would lower the freezing point sufﬁciently to
prevent freezing. However, there is evidence to suggest that the increase in sap
concentration ean solely account for a small increase in hardiness and may be
important only for tender plants, unable to survive freezing (Levitt, 1956). In certain
plants, such as hardy winter cereals, cell wall polysaccharides seem to play a role in
hardiness by interfering with ice formation. Such interference resulted in more
imperfect ice crystal development, which was associated with hardier tissues (Olien,
1965 , 1967).

Two other roles of carbohydrates, with more pronounced effects on hardiness
have been proposed: carbohydrates might increase hardiness by providing the energy
required for the hardening processes or by preventing the denaturation of proteins
(i.e.,act as eryoprotectants) (Howell and Stackhouse, 1973).

Energy is needed for the acquisition of cold hardiness and its maintenance
during mid-winter, and for hardiness recovery (rehardening) after spells of warm
weather. Carbohydrates might therefore be important to meet these energetic

demands (Howell, 1988).

 

II
A

(‘7

15

In many plants, exposure to low temperatures leads to the accumulation of
eryoprotectants, namely the carbohydrates sucrose, rafﬁnose, and sorbitol. Of these,
sucrose is the most commonly found in freezing-tolerant species (Guy, 1990). It was
suggested that sugars might exert a direct protection of proteins either by replacing
the water of hydration of the protein or by increasing the ﬁrmness of water binding
(Steponkus and Lanphear, 1968). Sugars might also stabilize the membranes by
interacting with the polar headgroups of the phospholipids (Anchordoguy et a1. ,
1987). The role in membrane stabilization is of primordial importance, as several
studies have indicated that cell membranes are one of the major targets of freezing
injury, if not the primary site of injury (Steponkus and Wiest, 1978; Levitt, 1980;
Palta at al., 1981;Steponkus, 1984).Heber and Santarius (1964), for instance, showed
that in mitochondria and chloroplasts, sucrose could prevent the uncoupling of
phosphorylation resulting from freezing.

Regardless of the mode of action of carbohydrates, and despite the fact that
a cause-effect relationship between sugar levels and cold hardiness is not established,
a high level of stored carbohydrates is considered important for cold hardiness of
grapevines (Howell, 1988; Wample at al, 1988), and other woody perennials such as
sour cherry (Howell and Stackhouse, 1973). Therefore, cultural practices that
optimize light interception by the foliage (e. g. adequate training and pruning) and
contribute to healthy leaves (e.g. pest and disease control) are important to increase
hardiness because they result in improved carbohydrate production (Howell and
Dennis, 1981; Howell, 1988).

Photoperiod was shown to induce cold acclimation in some woody species. In

16
apple trees (Howell and Weiser, 1970) and red-osier dogwood (van Huystee at al. ,

1967) cold acclimation occurs in two stages. The ﬁrst stage is probably triggered in
nature by short days (or, preferably, long nights) even though short days are not a
necessary prerequisite for acclimation. Indeed, the ﬁrst hardiness plateau (-25°C to
-30°C in Haralson apple) can be induced not only by short days m; x, but also by
low temperature (Howell and Weiser, 1970). Other factors such as endogenous
growth cycles or radiation quality may also be involved in the ﬁrst stage of
acclimation (Howell and Weiser, 1970). Temperature seems to be an absolute
prerequisite for the second stage of acclimation, which can result in survival to
temperatures as low as -55°C in Haralson apple trees (Howell and Weiser, 1970) or
-196°C in red—osier dogwood (Smithberg and Weiser, 1968).

In stems of pine and English ivy and in the bark of black locust, a single-stage
acclimation is observed, as quoted by Wolpert and Howell (1985b). This does not
necessarily imply that photoperiod is not involved, given that the onset of low
temperatures may coincide with the short-day effect, resulting in a single-stage
pattern of acclimation (Wolpert and Howell, 1985a).

Photoperiodic effects on cold acclimation are probably associated with the
production of translocatable hardiness promoters in ‘short day’ leaves (Irving and
Lanphear, 1967c) and of cold hardiness inhibitors in ‘long day’ leaves (Irving and
Lanphear, 1967b). In contrast, no translocatable factors seem to be involved in the
10W temperature-induced cold acclimation (Howell and Weiser, 1970).

In grapevines, photoperiod does not seem to inﬂuence acclimation (Wolpert

and Howell, 1986b). It has often been assumed that growth cessation is a prerequisite

17

for the development of cold acclimation, even though it was shown that dormancy
is not required (Irving and Lanphear, 1967a,b; Howell and Weiser, 1970). Growth
cessation in grapevines seems to be under photoperiodic control, but the nwd of
growth cessation for cold acclimation in this species is questionable (Wolpert and

Howell, l986a,b)

Leaf Removal Effects on Vine Growth and Yield

Intersection

Leaf removal is a recognized canopy management practice to improve the
microclimate in the cluster zone, and thereby enhance ripening and reduce fungal
diseases, namely bunch rot caused by 39mm; mere-a Pers. (Winkler at al., 1974;
Weaver, 1976; Wolf et a1., 1986;Gub1er, 1987; Kliewer and Bledsoe, 1987; Koblet,
1987, 1988; Bledsoe at al., 1988; Smith at al., 1988; English at al., 1989). However,
because leaf removal represents the removal of the main source of photosynthates,
this practice ean have a negative impact on the carbohydrate status of the grapevine
and, therefore, on vine growth (Buttrose, 1966; Kliewer and Fuller, 1973; Howell at
al., 1978), yield components (Weaver, 1963; Buttrose, 1966; May at al., 1969; Kliewer,
1970; Kliewer and Antcliff, 1970; Howell at al., 1978; Mansﬁeld and Howell, 1981;
Candolﬁ-Vasconcelos and Koblet, 1990), and cold hardiness (Stergios and Howell,
1977; Howell at al., 1978; Mansﬁeld and Howell, 1981).

Several authors suggested that grapevines can compensate, to some extent, for

losses in the functional leaf area by increasing the photosynthetic activity of the

18
remaining foliage and by expanding the leaf area on lateral shoots (Buttrose, 1966;

Kliewer, 1970;1(liewer and Fuller, 1973;Hofacker, 1978; Hunter and Visser, l988a,b;
Koblet, 1988; Reynolds and Wardle, 1989a; Candolﬁ-Vasconcelos, 1990; Candolﬁ-
Vasconcelos and Koblet, 1990). Moreover, Hofacker (1978), Hunter and Visser
(1989) and Candolﬁ-Vasconcelos (1990) reported that defoliation increased the
chlorophyll content of the remaining leaves.

Photosynthetic compensation for biological or physical leaf injury has also
been reported for fruit (Hall and Ferree, 1976; Proctor e_t al., 1982) and forest
species (Bassman and Dickmann, 1982), among others. Kriedemann (1977) attributed
the increased photosynthetic rate following leaf removal to enhanced stomatal
opening, increased enzyme activity, and freer earbohydrate movement to the growth
sites. Candolﬁ-Vasconcelos (1990) observed that leaf removal led to an increase in
both stomatal and mesophyll conductances, in agreement with previous reports
(Kriedemann, 1977).

Compensation may only be partial (Chaves, 1986; Candolﬁ-Vasconcelos,
1990), and this might explain, for instance, why in the study of Kliewer and Fuller
(1973) a signiﬁcant decrease in the growth of roots, trunks and shoots was observed
in severely defoliated vines (Chaves, 1986).

The ultimate response of a particular grapevine cultivar to leaf removal will
depend not only on the technique of removal by itself but also on environmental

factors, as will be discussed in the following sections.

 

 

Buttrose (1966) studied the effects of defoliation on the growth of roots,
stems, and berries in cv. Muscat of Alexandria. He found that root dry weight was
the most affected parameter, followed by dry weight of berries, shoots and trunks. In
contrast, Kliewer and Fuller (1973) reported that in Thompson Seedless, leaf removal
reduced more severely the accumulation of dry matter in the trunk than in the roots
and canes.

Several authors reported a reduction in berry weight following defoliation
(Weaver, 1963; Buttrose, 1966; May at al., 1969; Kliewer and Antcliff, 1970; Kingston
and van Epenhuij sen, 1989). Others observed a decreased bud fruitfulness (number
of clusters per node and/or number of berries per cluster) (May at al. , 1969;
Mansﬁeld and Howell, 1981). In cv. Thompson Swdless, May et a1. (1969) reported
a 10% to 80% reduction in yield per node in the season following defoliation, the
effect increasing with increased defoliation. Most of this reduction was accounted for
by a decrease in the number of clusters per node (May :21 al., 1969). Similarly, leaf
removal was shown to reduce ﬂower bud initiation in fruit trees such as plums,
apples, pears, and cherries (for references see Jackson and Sweet, 1972). The effect
of leaf removal on ﬂower initiation might be attributed to a loss of photosynthates
or to a change in the hormonal balance (Jackson and Sweet, 1972).

The above results sharply contrast with those of Kliewer and Bledsoe (1987)
and Bledsoe et a1. (1988). In studies with Sauvignon blanc grapevines, these authors
observed that leaf removal improved fruit composition without affecting the yield

components (cluster number and weight, berry weight). Moreover, in the same

,,
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20
cultivar, Kliewer at al. (1988) observed that, on average over a period of three years,

neither time nor severity of leaf removal signiﬁcantly affected the yield components.
In the third year of the trial, the vines subjected to the most intense leaf removal
(removal of basal leaves plus leaves at the top of the canopy) were even signiﬁcantly
superior in number of clusters per shoot, ﬂowers per inﬂorescence, and fruit set.

Some factors that may account for the discrepancies observed include: a)
variety and clone; b) site climate; c) fruit exposure to sunlight; d) light environment,
age, and position of the leaves removed; e) timing and severity of removal, and t)
vine size (Kliewer and Bledsoe, 1987; Reynolds and Wardle, 1989b; Zoecklein, 1989).

Bledsoe et a1. (1988) noted that most of the defoliation work preceding their
study had been done on cv. Thompson Seedless in hot climates and used severe
defoliation. Under these conditions, the berries would receive a substantial amount
of direct solar radiation after defoliation, and their temperature could increase
considerably. Radler (1965) reported that a high temperature by itself signiﬁcantly
reduced berry weight in cv. T. Seedless. In contrast, the trial of Bledsoe at al. (1988)
was performed in a cool to moderate climate. Moreover, the number and position
of the leaves removed were such that the fruits were not exposed to direct solar
radiation for prolonged periods. This might explain the lack of berry weight reduction
(Bledsoe ct al.,1988).

Mansﬁeld and Howell (1981) found that partial defoliation (50%) of Concord
grapevines reduced cold hardiness and fruitfulness and delayed bud break in a

manner dependent on the distance between the foliated and the defoliated parts of

the vine.

 

 

 

 

21
In cv. Pinot noir, leaf removal within a critical period (up to 2-3 weeks after

full bloom) resulted in intense ﬂower and fruitlet abscision and reduced bud fertility,
thereby decreasing the current year’s and the following year’s yield. Moreover, the
presence of leaves on lateral shoots during fruit maturation was considered important
to assure fruit quality and adequate starch reserves in the wood (Candolﬁ-

Vasconcelos, 1990; Candolﬁ-Vasconcelos and Koblet, 1990).

I E E l E ii E . Q 1'

Some inconsistencies have also been found for the effects of leaf removal on
berry composition, which might be explained, at least in part, by the same factors
mentioned above.

Buttrose (1966) and Kliewer and Antcliff (1970) found a signiﬁcant decrease
in fruit soluble solids concentration, but in these studies an intense defoliation was
applied. Several defoliation experiments have been conducted in an attempt to assess
the leaf area required to mature a given weight of grapevine fruits. Numerous values
have been obtained, ranging from 0.5 to 1.7 mleg of fruit, depending upon variety
and experimental conditions (for references see Carbonneau at al, 1977; Chaves,
1986; Williams at al., 1987). In ﬁeld experiments to determine this relationship the
functional leaf area per vine, related to the canopy microclimate, has often been
overlooked which may account for the diversity of results obtained (Williams at al. ,
1987).

Kliewer :1 a1. (1988) reported that Sauvignon blanc grapevines with well

exposed fruits prior to leaf removal showed no signiﬁcant difference in fruit

22

composition relative to non-defoliated vines. In contrast, leaf removal improved fruit
composition in vines subjected to training systems eausing highly shaded fruits (4 to
5 % of ambient PPF). The removal of leaves around the cluster between fruit set and
veraison increased the total soluble solids and decreased the titratable acidity, malic
acid, pH, and potassium concentration in the fruits (Bledsoe at al., 1988; Kliewer at
al., 1988).

Smith et a1. (1988) noticed that the most marked effect of leaf removal on
fruit composition of Sauvignon blanc, Chardonnay and Cabernet Sauvignon was a
reduction in titratable acidity, largely due to a decrease in malic acid; no signiﬁcant
reduction was observed when leaf removal was applied after veraison.

Leaf removal may affect fruit composition as a result of a change in radiation
quality and temperature (Smart, 1987; Bledsoe et al.,1988; Zoecklein, 1989) and in
photosynthesis and pattern of assimilate movement (Quilan and Weaver, 1970;
Bledsoe at al., 1988; Zoecklein, 1989). Temperature will increase due to a greater
exposure to sunlight eaused by leaf removal. Such an increase, even if small, may
explain the increased soluble solids in the fruits and the reduced titratable acidity
and malic acid (Smart, 1982; Bledsoe at al., 1988; Kliewer gt a” 1988; Zoecklein,
1989). The increase in soluble solids may also result from enhanced photosynthetic
efﬁciency of the remaining leaves and increased movement of assimilates towards the
cluster, due to the removal of basal leaves (Bledsoe gt a1.,1988). Moreover, a higher
red/far red ratio was observed in the cluster region following leaf removal. This
would affect the activity of the phytochrome and thereby some phytochrome

regulated enzymes (e. g. malic enzyme, malic dehydrogenase, phenylalanine ammonia

23

lyase, and probably nitrate reductase), which are involved in reactions relevant for
fruit composition (see Smart, 1987, for references).

English et a1. (1989) studied the relationship between microclimate changes
brought about by leaf removal around the clusters, and the incidence and severity of
m bunch rot. Of the microclimate variables tested (temperature, atmospheric
humidity, wind speed, and leaf wetness), wind speed was the most affected by leaf
removal. However, the decrease in bunch rot associated with leaf removal was
related to interactions between the microclimate variables rather than to a change

in a single variable (English at al., 1989).

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Robertson, A.J.,L.V. Gusta, M.J.T.Reaney, and M. Ishikawa. 1987. Plant Physiol.
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Sakai, A. 1960. Relation of sugar content to frost hardiness in plants. Nature
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33

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34

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35

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Coop. Ext. Service, vol.4,no.6, pp. 1-9.

CHAPTERI

Influence of Basal Leaf Removal and Cropping Level on Leaf Gas Exchange,

Leaf Chlorophyll Content, Vegetative Growth, and Partitioning of Dry Matter

and N on-structural Carbohydrates in Seyval Grapevines

36

37
Abstract

Own-rooted Seyval grapevines, either one-year-old potted vines or mature,
ﬁeld-grown vines were subjected to source! sink manipulative treatments consisting
of basal leaf removal and cropping level.

On potted vines, leaf removal at berry pea size increased leaf net C02
assimilation rate (A), stomatal conductance (g,), and transpiration rate (E) at the
basal and middle-shoot leaf positions, while total leaf chlorophyll content was not
signiﬁcantly inﬂuenced; removal at veraison had no signiﬁcant effect on A, g,, and
E either on potted or on mature vines, and only a sporadic positive effect on WUE.
A, g,, and E were increased by the presence of fruits, specially on potted vines; the
cropping effect on water use efﬁciency (WUE) was minimal and no consistent
pattern was noticed. Fruiting (3C1) potted vines had higher leaf chlorophyll content
than non-fruiting (0C1) ones but this was apparently not decisive for the enhanced
A on the former.

Leaf removal had no signiﬁcant effect on vegetative growth and dry matter
accumulation and partitioning on potted vines. Cropping inﬂuenced dry matter
partitioning but not total dry weight; fruits developed at the expense of shoots, roots,
leaves and, to a lesser degree, of the trunk. The lower cane dry weight of 3C1 relative
to 0C1 vines reﬂected a reduction in shoot length, number of nodes, and intemodc
diameter; the lower leaf dry weight resulted from fewer leaves and reduced area per
leaf, while no signiﬁcant differences in speciﬁc leaf weight were found.

In the early fall, the soluble carbohydrate per unit of dry weight was higher

 

 

 

38
in eancs and trunk of 3C1 than of 0C1 vines; this was opposed to cane starch, both

on a dry weight and a volume basis, and to cane total non-structural carbohydrate
(TNC) on a volume basis. When all sampling dates were considered, 3C1 vines had
lower cane starch and TNC than 0C1 vines on a volume basis, but higher
concentration of starch and TNC in the trunk and of starch in roots; differences in
root soluble carbohydrate and TNC between cropping levels were not signiﬁcant.
Leaf removal had little effect on carbohydrate concentration. A signiﬁcant
effect was found for starch and TNC in roots if averaged across sampling dates;
levels in vines defoliated at pea size (R1) were higher than in vines defoliated at
veraison (R2), and similar (or higher, in the case of root TNC) to those of control
(C) vines. If only 3C1 vines are considered, cane soluble carbohydrate and TNC (on
a dry weight basis) at the March assessment were higher in R1 and C than in R2

vines.

Introduction

A number of studies in different crops have shown that the photosynthetic rate
per unit of leaf area may increase with an increase in the strength of the sink (either
reproductive or vegetative) relative to the size of the source (review by Flore and
Lakso, 1989).

In grapevines, the presence of fruits (Loveys and Kriedemann, 1974;
Kriedemann at al., 1975; Kriedemann, 1977; Chaves, 1984; Downton gt ﬂ., 1987) and

leaf removal (Hoﬁckcr, 1978; Hunter and Visser, 1988,1989; Reynolds and Wardle,

 

 

39
1989; Candolﬁ-Vasconcclos, 1990), which decrease the sourch sink ratio, were found

to enhance the leaf net CO, assimilation rate (A). Earlier research before gas
exchange systems were used, suggested the inﬂuence of the source/ sink ratio on the
photosynthetic rate based on dry matter accumulation in grapevines (Humphrics and
Thorne, 1964; Buttrose, 1966; May 91 11., 1969; Kliewer and Antcliff, 1970; Kliewer
and Fuller, 1973) and in other crops (Flore and Lakso, 1989).

Increased photosynthetic rate following leaf removal or a higher
photosynthetic rate of leaves on fruiting versus non-fruiting grapevines was shown to
be associated with decreased mesophyll resistance and increased stomatal
conductance (Kriedemann, 1977; Horackcr, 1978; Chaves, 1984; Candolﬁ-
Vasconcelos, 1990). However, the mechanism(s) responsible for a hypothesized
regulation of the source by the strength of the sink has not been elucidated (Flore
and Lakso, 1989). One hypothesis is the occurrence of end-product inhibition,
whereby the accumulation of carbohydrates in the leaf due to insufﬁcient sink
strength or to excessive carbohydrate supply would reduce the photosynthetic rate
(Neales and Incoll, 1968). However, hormonal changes (Loveys and Kriedemann,
1974; Kriedemann at al., 1975; Geiger, 1976; Hoad ct aI.,1977) and changes in the
orthophosphatc concentration (Walker and Herold, 1977) may also be involved in
the regulation of photosynthesis by sink activity (Flore and Lakso, 1989).

Although widely reported, the photosynthetic response to the sink strength is
not a general rule (Flore and Lakso, 1989). Moreover, despite the knowledge that
the photosynthesis of grapevine leaves may respond positively to leaf removal, there

is evidence that the enhancement of A as well as other compensatory responses such

 

 

 

40
as increased leaf area on lateral shoots (Kliewer, 1970; Kliewer and Fuller, 1973;

Wolf et a1., 1986; Reynolds and Wardle, 1989; Hunter and Visser, 1990) may only
partially compensate for the loss of leaf area (Candolﬁ-Vasconcelos, 1990).
Therefore, the use of basal leaf removal to improve the microclimate in the cluster
region must be viewed with caution due to the potential carbohydrate loss it
represents. The buds axillary to the basal leaves removed, located in the renewal
zone, will in part be retained at pruning and originate the growth and crop in the
following season. An adequate carbohydrate status of this particular cane region has
considerable practical implications. This aspect is of special relevance in cold climate
regions, because storage carbohydrates are probably involved in the physiological
processes leading to the development and maintenance of cold hardiness (Howell,
1988).

The inﬂuence of the source/ sink ratio on the photosynthetic rate has been
generally investigated by studying a certain manipulative treatment pg 5;. In only a
few instances have both leaf removal and the cropping effect been simultaneously
investigated in grapevines, and severe defoliation is usually applied. In the present
study, the source! sink ratio was manipulated by combining the removal of a few
basal leaves with total or partial cluster thinning. In two experiments, leaf removal
was applied at or shortly after veraison. Based on the relationship between
photosynthesis and leaf age reported by Kriedemann at al. (1970), the basal leaves
(at least those on non-fruiting shoots) would at this time be in the period of gradual
decline in photosynthesis. In another experiment, leaf removal at pea size (ﬁve weeks

after full bloom) was also investigated. The effects of these manipulations on gas

 

41

exchange parameters of grapevine leaves (namely on A), leaf chlorophyll content,
vine growth, leaf area, dry matter partitioning, and levels of non-structural
carbohydrates (starch and soluble carbohydrates) in below and above-ground vine
parts were studied. Some questions addressed were: a) Is photosynthesis of grapevine
leaves sensitive enough to respond to the removal of a few basal leaves on mature
and on young vines under differing cropping levels? b) Is there an effect of the
source! sink manipulations performed on the total dry matter production and/or
distribution? c) In particular, is there an effect of leaf removal and cropping level on
non-structural carbohydrate concentration, namely in the restricted region of the cane

subjected to leaf removal?

Materials and Methods

W
Experiments I and II

These experiments were conducted at the Horticultural Research Center
(HRC), East Lansing, Michigan, using one-year-old own-rooted Seyval (Seyve-Villard
5-276) grapevines. The vines were weighed and planted in May/1989 (Experiment
I) or in May/1990 (Experiment II) in 19 1 pots containing a sterilized loam, sand and
peat mixture with good water holding and aeration properties. The potted vines were
placed in a ﬂat gravel-covered area at a 1.0 m x 1.2 m spacing which allowed good
light exposure, and trained to two shoots. Vines were irrigated, fertilized (using a

Peter’s 20-20-20 solution), and sprayed for pest and disease control as needed.

 

 

 

42

Cropping level and leaf removal treatments were arranged as a two-factor
factorial, set in a randomized block design; vine fresh weight at planting was used as
the blocking variable.

Cropping level was either 0C1 (no clusters per vine) or 3C1 (three clusters per
vine) and was imposed on June 22/89, four days before full bloom (Experiment I),
or July 4/90, ten days after full bloom (Experiment H). On the vines thinned to three
clusters, the basal cluster on one shoot and two clusters (the basal and the second)
on the other shoot were retained. In Experiment I leaf removal levels were: C = no
main leaves removed (control), and R = leaf removal near veraison (August 31/89,
nine weeks after full bloom). In Experiment 11 leaf removal levels were C = control,
R1 = leaf removal at pea size (July 27/90, ﬁve weeks after full bloom), and R2 =
leaf removal at veraison (August 21/90, eight weeks after full bloom). Leaf removal
consisted of removing three consecutive leaves in the fruiting region of both vine
shoots. On fruiting vines, the leaves opposite, one node above and one node below
the basal cluster were removed; on non-fruiting vines, leaves were removed from
equivalent node positions. To avoid the variability associated with the erratic growth
of lateral shoots (Buttrose, 1968), these shoots were removed at weekly intervals,

regardless of the treatment combination.

Experiment III
Own-rooted, mature, bearing Seyval grapevines at the Clarksville Horticultural
Experimental Station (CHES), Clarksville, Michigan, were used in this experiment.

The vineyard was planted in 1983 in a Kalamazoo sandy loam soil with vine spacing

43

of 2.4m x 3.0 m within and between rows and a N-S row orientation. The vines were
trained to Hudson River Umbrella (a bilateral cordon at the top wire), with the top
wire at 1.8 m height. The vines were balanced-pruned each. year using a 15+10
pruning formula (15 nodes retained for the ﬁrst 0.45 kg of dormant one-year cane
prunings plus 10 nodes for each additional 0.45 kg), up to a maximum of 65 nodes
retained per vine. Fertilization, irrigation, and pest and disease control were done
according to standard procedures at CI-IES.

Prior to the 1989 growing season a randomized block design was established.
Vine size (weight of one-year old cane prunings), which varied between 1.0 and 1.5
kg, was used as the blocking variable. Five blocks of six vines were deﬁned, one vine
per treatment combination.

Leaf removal and cropping level treatments were arranged as a 2x3 factorial.
The leaf removal levels were: C = no leaves nor lateral shoots removed (control);
R = main leaves and lateral shoots removed at three basal nodes on all the shoots
of the vine, the same node positions defoliated in Experiments land 11. The cropping.
levels were: 0 = 0 clusters per vine; 1.5 = 1.5 clusters per node retained at pruning;
NT = all clusters left (no thinning). lateral shoots were allowed to develop normally,
except for those at the three treated nodes on R vines. Each vine was subjected to
the same treatment combination in 1989 and 1990. The data herein reported were
collected in 1990. In this season, cluster thinning was applied on June 27 (nine days
after full bloom) and leaf removal on August 15 (veraison, eight weeks after full

bloom).

Wests

Gas exchange measurements on attached leaves were made on several
occasions during the vegetative season using an ADC LCA-2 portable open gas
exchange system (Analytical Development Co. Ltd. , UK). The measurements were
taken between 10:30H and 14:00H on well exposed leaves, with PPF above 1000
pmol m‘zs“ and leaf temperature between 24°C and 33°C, depending on the
measurement date. At the time of measurement the leaves were held normal to the
incident radiation. The time interval selected for gas exchange measurements
represented a compromise between the number of measurements to take and the
proximity to the 11:30H to 14:00H period, during which the photosynthetic rate of
leaves on potted Seyval grapevines was found to remain relatively stable around the
maximum value (Edson, 1991). Measurements were taken on successive blocks of
vines, each block including one vine per treatment combination under evaluation. In
Experiment 11, only control vines (C/OCl and C/ 3C1) and vines defoliated at pea size
(RI/0C1 and R1/3Cl vines) were used.

Measurements were taken on two (Experiments 1 and III) or one
(Experiments II) shoots per vine on four (usually) or three replicates per treatment
combination (eight or six replicates before leaf removal). Three leaves along the
shoot were measured, except for the ﬁrst measurement in Experiments land 11, when
only two leaves per shoot were used due to the still reduced shoot length. The leaves
measured were: 1) Basal leaf (BAS) - leaf usually at nodes three or four from the
base on the measurements prior to leaf removal and at nodes ﬁve or six thereafter;

2) Middle shoot leaf (MID); 3) Apical leaf (AP) - in 1989 (Experiment I) the most

 

1"

 

45
recently fully expanded leaf; in 1990 (Experiments II and III) a leaf near full size (80-

90%), the most apieal leaf with a hardened blade.

Net CO, assimilation rate (A), stomatal conductance (g,), transpiration rate
(E) and water use efﬁciency (WUE), were calculated using a BASIC program
developed by Moon and Flore (1986). When two shoots per vine were measured, the
ealculated values for the gas exchange parameters were averaged by leaf position

before statistical analysis.

Chlorophyll Eamn'bn and Analysis

Leaf chlorophyll content was measured on four vines of Experiment 11 other
than those used in gas exchange determinations but treated exactly the same way. As
in the gas exchange measurements, only R1 and control vines were sampled. Ten leaf
discs of 0.3378 cm2 each were taken from BAS, MID, and AP leaves of each vine on
August 24/90 (veraison) and September 19/90 (just before harvest). Five discs per
leaf were used for chlorophyll extraction while the others were dried at 55°C and
weighed to determine the speciﬁc leaf weight.

Chlorophyll extraction was based on Moran and Porath (1980). The ﬁve leaf
discs per leaf were kept immersed in 9 ml of DMF (N ,N—dimethylformamide) in
darkness at 5°C for 30 hours. The absorbancc of the extract was then measured at
664 nm, 647 nm and 625 nm, using a Spectronic 1001 (Bausch & Lomb)
spectrophotometer. Chorophst a and b, and total chlorophyll (chlorophst a + b)
were calculated as in Moran (1982). The total chlorophyll per unit of leaf area and

of leaf dry weight were determined, as well as the chlorophyll a/b ratio.

 

Shoot length, the number of nodes per shoot, leaf area, and leaf dry weight
were measured on both vine shoots of six replicates at the end of the 1989
(Experiment I) and 1990 (Experiment 11) growing seasons. In Experiment 11 the
diameter of the ﬁfth intemodc from the base of each shoot was also determined (as
the average over two perpendicular axes) and the mean value per vine was
calculated. Total leaf area per vine was measured using an area meter (model L1-
3000 from Li-Cor Inc., Nebraska, USA). Leaves were then oven-dried at 65°C until
constant weight, and dry weight was recorded. The dry weight of the blades and the

total leaf area per vine were used to calculate the speciﬁc leaf weight.

11 II E . . .
Part of the vines from Experiment II were partitioned in the early fall

(September 30/90), mid-winter (January 10/91) and late winter (March 14/91). Nine
blocks of vines were distributed by three groups (lighter, medium and heavier)
according to vine weight before planting. One block per group was randomly selected
to be partitioned at each date. The vines partitioned in January and March were kept
outdoors during the dormant season, mulched with straw up to most of the trunk
height.

For the vines partitioned on September 30, the parts considered were: leaves,
clusters, current year’s shoots, trunk, and roots. The clusters were included in the
calculations relative to these vines even though they had been harvested on

September 19. In the mid- and late winter, vines were partitioned into canes (current

47

year’s shoots after leaf fall), trunk, and roots. For ease of expression the current
year’s shoots of the vines partitioned on September 30 will also be denominated
‘eanes’. The separation between the root system and the above-ground part of the
vine was done at 2 cm above the uppermost insertion of the roots, a criterion
previously adopted by Edson (1991). After sampling for non-structural carbohydrate

analyses, the vine parts were oven-dried at 65°C until they achieved constant weight.

 

Non-structural carbohydrates (starch and total soluble carbohydrates) were
measured in cane, root, and trunk samples collected on each vine partitioned
(Experiment 11). A cane segment was taken from both vine canes between nodes
three and four. A segment of 3 to 5 cm long was taken from the basal end of the
trunk. The root fragments sampled had a diameter of 2-3.5 mm and were well
distributed throughout the root system. The length of the trunk and cane segments
as well as the diameter across two transverse axes were measured for further volume
estimation, assuming the transverse section to be elliptical. As the tissue samples
were prepared, they were frozen in liquid nitrogen and then stored at -20°C. Prior
to starch analysis, the samples were freeze-dried, weighed, ground in a Wiley mill,
and passed through a 40—mesh screen. Fifty milligrams per sample were extracted
four times using 2 ml of 80% ethanol per extraction. The homogenates were
centrifuged at 3000xg for 5 min. after each extraction. Soluble carbohydrates were
measured in the supernatants collected from the successive extractions, and starch

in the remaining pellet, after evaporation to dryness using a Savant speedvac SC200

48

(Savant Instruments Inc., NY). Starch was measured using the method described by
Roper et a1. (1988). The pellets were heated in acetate buffer (0.1 M, pH 5.0) and
then incubated for 16 h at 55°C with amyloglucosidase (Boehringer Mannheim 208
469). The glucose produced was colorimetrically assayed after reaction with PGO
enzymes in the presence of o—dianisidine dihydrochloride (Sigma Chemical Co.).
Absorbance at 440 nm was read with a Hitachi U-3110 UV/Vis spectrophotometer

(Hitachi Ltd. , Tokyo). Each sample was assayed three times. Soluble carbohydrates
were measured by spectrophotometry (absorbance at 620 nm) after reaction with
anthrone reagent (2 g anthrone/l 95 % sulfuric acid) as described by Flore et a1.
(1983), except for the blanks used. Instead of using water as a blank, individual
blanks for each sample extract were prepared by adding 1 ml of extract to 5 m1 of
water. Each sample was assayed three times. Appropriate glucose standard curves

were used as reference for starch and soluble carbohydrate determinations.

5"]!1'

Leaf removal and cropping level (when both present) were analyzed as a two
factor factorial set in a randomized block design. The effects of cropping level and
leaf removal on gas exchange parameters were evaluated per leaf position at each
measurement date. The effect of leaf position was evaluated at selected measurement
dates in the season; in these analyses, leaf position was considered a split-plot on
cropping and leaf removal (or on cropping alone, before leaf removal imposition).
In all the analyses where two or more sampling dates were combined, sampling date

was included as a blocking variable.

49
Data were analyzed by analysis of variance, using either the MSTAT-C

software package (MSTAT Development Team, 1990) or the GLM (from General
Linear Models) procedure of the Statistical Analysis System package (SAS Institute
Inc., 1985). Percentage data were subjected to the arc-sine of the square root
transformation prior to analysis of variance. When the F-values were signiﬁcant at
a 5% or lower level, mean separation was done using the LSD test or an equivalent
test of the GLM procedure for the least-squares means. All mean separation tests
were done at the 5 % level. In Experiment II, when leaf removal had a signiﬁcant
effect and did not signiﬁcantly interact with cropping level, orthogonal contrasts were
used to compare the control against the average of the two leaf removal dates, and

also the ﬁrst against the second date.

Results

WW
Prior to treatment imposition, no signiﬁcant differences were found in any gas
exchange parameters analyzed among the vines that were to be subjected to the

different treatment combinations (data not shown).

Cropping Level Eﬂ’ects
0n potted vines (Experiments I and II), the presence of fruits was almost
invariably associated with higher A (signiﬁcantly or not), regardless of the leaf

position (Tables 1 and 2). On average through the whole season, the fruit effect on

 

50

1a8le 1. Influence of leaf removal and cropping level on the net co, assimilation rate (A) of 8A8, HID,
no AP leaves of potted Seyval vines ("RC 1989 - Experiment I).

 

A (amol co,.m".s") Average
Leaf Treatment'
position‘

 

Jute 28 July 11 Aug.21 Aug.25 Aug.30 Sep.12 Sep.18 Over the Since leaf
2 d 2 wk 8 uk V 5 d 2.5 wk 1 wk mole removal

PFB" PFB PF8 P1! P1! 811 season i aposi tion

 

8A8 Leaf rueval

c 6.37 5.09 5.52
R 6.42 5.76 5.98
ns‘" ns ns
Crop. level

OCl 10.90 12.08 5.318 6.76 7.998 6.48 4.88 7.968 5.41
3Cl 12.12 12.41 7.828 8.26 10.678 6.31 5.97 9.388 6.09

ns ns * ns * ns ns ”1' ne
Interaction ns ns ns
HID Leaf removal
c 8.50 7.81 8.04
R 7.79 7.81 7.81
ns ns ns
Crop. level
OCI 11.468 7.818 8.78 10.288 6.82 6.328 8.548 6.498
3ct 12.79a 11.03a 12.07 15.00a 9.47 9.31a 11.36a 9.36a
*9 t “8 if m i "t n
Interaction ns ns ns
AP Leaf removal
c 10.54 9.23 9.67
R 11.10 8.85 9.60
ns ns ns
Crop. level

OCl 7.59!) 7.12 8.36!) 10.66 12.62!) 10.53 7.52b 9.2‘b 8.52b
301 9.258 7.52 11.838 13.55 16.238 11.12 10.568 11.678 10.748
* m C m C m if “C ”

Interact 1 on ns ns ne

 

'8A8:8esal; HIO:middle shoot; AP:apical

‘12: control (no leaves removed); R: leaves removed on Aug. 31/89 (near veraison)
001: 0 clusters per vine; 3CI: 3 clusters per vine

'Time in days (at) or weeks (wk) relative to vine phenophases

me post full bloom: V: Veraison; PV:post veraison: 811:8efore harvest
”m, *, '1', m Ion simificant or significant at 51,18 or 0.1% level, respectively.

 

Table 2. Influence of leaf removal and cropping level on the net co, assimilation rate (A) of BAS, MID,

51

and AP leaves of potted Seyval vines (NRC 1990 - Experiment II).

 

 

 

 

A (amol 00,.m'2.s") Average
Leaf on’ Ireatmnt'
iti '
pos July 19 July 25 Aug.2 Aug.9 Aug.29 Sep.13 Sep.26 Over the Since leaf
3.5 at: 4.5 wk 5.5 at 6.5 uk 1 uk 1 wk 1 wk mole removal
”8' PFB PFB PFB PV 8|! PH season i nposi t i on
8A8 Leaf removal
c 13.10 13.168 13.41 10.66 4.568 10.988
R1 14.82 14.99a 14.38 9.56 5.88a 11.93a
m" C m m C *
Crop. level
OCI 12.00 12.92 12.94 13.84 11.698 7.338 5.66 10.798 10.298
3Cl 13.22 13.31 14.98 14.31 16.10a 12.89a 4.79 12.76a 12.61a
'13 1'18 "8 "s m t" US it. an
Interaction ns ns ns ns ns ns
HID Leaf removal
c 13.328 13.158 13.90 12.55 6.698 11.928
R1 16.50a 15.01a 14.36 12.31 8.43a 13.32a
* i "S "3 it it
Crop. level
OCl 12.448 13.79 12.868 12.378 10.528 8.03 11.648 11.518
361 15.63a 16.03 15.30a 15.89a 14.33a 7.10 13.981: 13.73a
it "8 it t it "8 iii an
Interact i on ns ns ns ns ns ns
AP Leaf removal
I: 9.63 10.76 11.93 10.86 4.50 9.54
R1 11.14 12.24 11.50 10.33 4.62 9.97
ns ns ns ns ns ns
Crop. level
0Cl 7.058 9.21 9.30 9.758 10.478 8.498 4.51 8.428 8.508
3Cl 9.32s 10.90 11.46 13.25a 12.96a 12.70a 4.62 10.79a 11.00a
. "8 m u i * m i.‘ t“
Interaction ns ns ns ns ns ns
‘8A8:8esal; hID:middle shoot; AP:apical
'c: control (no leaves removed); R1: leaves removed on July 27/90 (pea size)
001: 0 clusters per vine; 3CI: 3 clusters per vine
'Iime in weeks (alt) relative to vine phenophases
PFB: post full bloom; PV: post veraison; 811: before harvest; PH: post harvest
"ns, *, '1', ”1' Non significant or simificant at the 51,11 or 0.1% level, respectively.

#1
il

52

Table 3. Influence of leaf removal and cropping level on the net (:02 assimilation rate (A) of BAS, HID,
and AP leaves of nture field Seyval vines (CHES 1990 - Experiment III)

 

 

 

A (amol co,.m".s") Average
Leaf position‘ Treatment'
July 18 Sept. 4 Sept. 25 Oct. 6 Over the Since leaf
4 wk PFB‘ 3 wk PV It 10 d PH whole removal.
season mposttron
BAS Leaf removal
c 11.57 8.66 6.69 9.18
R 11.01 9.54 6.32 9.19
ns"' ns ns ns
Crop. level
0 9.36 10.40 9.89 7.14 9.33 9.32
1.5 10.23 11.38 9.00 6.55 9.42 9.20
II 9.95 12.08 8.42 5.80 9.23 9.04
ns ns ns ns ns ns
Interaction ns ns ns ns
HID Leaf removal
c 14.39 12.11 9.25 12.16
R 13.32 12.17 10.45 12.12
ns ns ns ns
Crop. level
0 11.55 12.87 12.06 11.52 12.06 12.20
1.5 12.40 14.65 11.67 9.41 12.19 12.14
81’ 12.62 14.05 12.69 8.63 12.19 12.08
ns ns ns ns ns ns
Interact i on ns ns ns ns
AP Leaf removal
c 11.94 11.58 11.89 11.79
R 10.64 11.88 10.89 11.16
ns ns ns ns
Crop. level
0 5.83 7.948 10.588 11.80 9.078 9.958
1.5 7.27 12.74a 12.77a 12.40 11.50a 12.66a
NT 7.49 13.20a 11.83a8 9.98 10.89a 11.82a
m it i m it *
"EM" ns ns ns ns

 

 

 

‘8AS:8asal; RIO:middle shoot; AP:apical
'c:control (no leaves removed); R:leaves removed on Aug. 15/90 (veraison)

0:0 clusters per vine; 1.5:1.5 clusters per node retained; ltzmthimed. Thinning date: Jme 27/90.
'Iime in days (d) or weeks (wk) relative to vine phenophases

PF8:post full 8loom; PV:post veraison; ll:harvest; Pll:post harvest
""ns, *, “, 1'” Ion simificant or significant at 5%, 1% or 0.1% level, respectively. Mean separation

within column using the LSD test at 5%

 

53
A was highly signiﬁcant at every leaf position in both experiments with potted vines.

The overall increase in A on 3C1 relative to 0C1 vines at BAS, MID, and AP leaves
was, respectively, 18%, 33%, and 26% in Experiment I (Table l) and 18%, 20%, and
28% in Experiment 11 (Table 2); an enhancement as high as 76% was found at BAS
leaves in Experiment 11 one week before harvest. The response of mature ﬁeld vines
(Experiment III) to cropping was less marked than that of potted vines; only at the
AP leaf position was a signiﬁcant fruit effect on A observed (Table 3). In Experiment
I, the presence of fruits increased A at the AP leaf position as early as two days after
full bloom (Table 1). However, neither at this time (data not shown) nor at two
weeks after full bloom (Table 4) was the cropping effect signiﬁcant when all the leaf
positions were considered, unlike at the ﬁrst measurement in Experiment 11, 3.5
weeks post full bloom (Table 5). On mature vines, A was higher on fruiting (1.5 and
NT) than on non-fruiting (0) vines three weeks after veraison if leaf positions were
analyzed together (Table 6). In the experiments conducted, g, and E at each leaf
position were, like A, usually higher on fruiting than on non—fruiting vines, and
signiﬁeantly higher when all the sampling dates were considered (except for E at
MID leaves in Experiment III); cropping effects on WUE were seldom signiﬁcant,
regardless of the leaf position (Appendix A). When the leaf positions were combined,
the SC] vines had higher WUE than the 0C1 vines at 3.5 weeks post full bloom in
Experiment 11 (Table 5), while WUE was higher on non-fruiting than on fruiting ﬁeld

vines at harvest (Table 6).

 

54

 

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57

Leaf Removal Eﬁ‘ects

Leaf removal at pea size (R1) increased A, g,, and E at the BAS and MID
leaf positions (Experiment 11) at either one or both measurements in the pre-veraison
period (August 2 and August 9, one and two weeks after leaf removal, respectively),
at the post-harvest measurement, and on average across the measurements following
leaf removal (“fable 2; Appendix A). The AP leaf position showed no signiﬁcant leaf
removal effect on A, and a signiﬁcant effect on g, and E was observed only once.
Leaf removal at on shortly after veraison whether on potted (Experiment I) or on
ﬁeld vines (Experiment 111) had no signiﬁcant effect on A, g,, and E (Tables 1, 3, 4
and 6; Appendix A), and no or only a sporadic effect on. WUE at each leaf position
(Appendix A). When leaf positions were analyzed together, a signiﬁcant leaf removal
effect on WUE was found on ﬁeld vines at harvest (Table 6). Whenever the leaf

removal effect was signiﬁcant, WUE was higher on defoliated than on control vines.

Willem
The total chlorophyll content of BAS leaves was not signiﬁcantly affected by

leaf removal at pea size nor by cropping level; a tendency for higher chlorophyll
levels at BAS leaves of R1 than of C vines, and of SC] than of 0C1 vines was
observed, though (Table 7). At MID and AP leaves there was no clear pattern of
response in total chlorophyll to leaf removal. At these leaves, the chlorophyll content
on a dry weight basis was higher on 3C1 than on DC] vines both at veraison and at
harvest; on a leaf area basis this effect was also evidenced, except that at harvest it

was signiﬁcant for the MID leaves of R1 but not of C vines (data not shown).

58

table 7. Influence of leaf reaoval and cropping level on the total chlorophyll contentﬁ chlorophyll a/b
ratio, and specific leaf Height (SLH) of us, HID and AP leaves of potted Seyval Vines at veraison
(Amt 24) and at harvest (Septedser 19) (HRC 1990 - Experth II).

 

Total chlorophyll (chl. a + b)

 

 

 

Leaf Treatment' chlorophyll a/b sw (an/cal’)
poeition‘ “ml? 3“ an Height
Veraison Harvest Veraison Harvest Veraison Harvest Veraison Harvest
us Leaf ranoval
c 43.52 29.10 7.00 4.42 4.17 3.36 6.22 6.62
Ill 48.62 31.73 7.77 4.62 3.88 3.46 6.26 7.00
ns' ns ns ns ns ns ns ns
Crop. level
on 44.37 28.82 6.91 4.13 3.98 3.47 6.42 7.02
3Cl 47.77 32.02 7.86 4.90 4.07 3.35 6.06 6.59
ns ns ns ns ns ns ns ns
Interaction ns ns ns ns ns ns ns "
HID Leaf removal
c 46.54 35.84 7.71 5.63 4.28 3.68 6.06 6.39
R1 48.73 30.37 8.22 4.91 4.07 3.55 5.94 6.26
ns (*) ns ns ns ns ns ns
Crop. level
OCl 44.611: 29.79 7.46b 4.61b 4.14 3.57 6.00 6.46
3Cl 50.66a 36.42 8.48a 5.94a 4.21 3.65 6.00 6.19
* l") "' ** ns ns ns ns
Interaction ns * ns ns ns ns ns ns
AP Leaf realoval

c 27.71 14.75 6.78 3.10 3.59b 3.50 4.08 4.88
R1 24.92 17.23 6.01 3.55 4.24a 3.25 4.15 4.91
ns (‘l ns ns * ns ns ns
Crop. level
001 23.13!) 12.86 5.54!) 2.521) 3.87 3.15 4.17 5.12s
3Cl 29.49a 19.12 7.25a 4.13a 3.96 3.60 4.07 4.67b
or (area) ea eee ns ns ns .
Interaction ns * ns ns ns ns ns ns

 

‘BAS:basal; HIDaiddle shoot; ”apical

'C:control (no leaves reaoved): Ill:leaves reaoved on July 27/90 (pea size)

OCI:0 clusters per vine; 3Cl: 3 clusters per vine

'ns, *, *‘, ”1' Hon significant or significant at the 5%, 1% or 0.1% level, respectively. Brackets

indicate that the factor is involved in significant interactions; therefore no mean separation was
perforued for the pain effect.

59

Neither leaf removal at pea size nor cropping level had a signiﬁcant effect on the
chlorophyll a/b ratio, except for AP leaves at veraison, when the ratio was higher on

R1 than on C vines (Table 7).

1!! . E l I 1'. l l E . . i

Leaf removal had no signiﬁcant effect on shoot growth, leaf area, and speciﬁc
leaf weight on potted vines (Tables 8 and 9), nor on total dry matter accumulation
and distribution among vine components whether at the end of the 1990 season
(Table 10) or when the partitioning dates were combined (Table 11).

Cropping level had no signiﬁcant effect on the total dry weight per vine at the
end of the season (Table 10), but inﬂuenced dry matter allocation (Tables 10 and
11). The fruits represented approximately 45% of the overall dry weight of 3Cl vines.
Fruit development was detrimental to dry matter accumulation in all the vegetative
fractions considered; the canes (leaves excluded) were the most affected, followed
by roots, leaves and trunk. Cane dry weight was decreased by about 70% due to the
presence of fruits, while a reduction of about 40% was found in the dry weight of
roots and leaves and of 18% in trunk dry weight. The lower cane dry weight of the
3Cl vines reﬂected highly signiﬁcant differences in shoot length, number of nodes,
intemodc length and intemodc diameter between cropping levels (Table 9). The
lower leaf dry weight resulted from a lower leaf area per vine due to a reduction in
both the number of leaves (nodes) and the area per leaf; the speciﬁc leaf weight did
not signiﬁcantly differ between SCI and DC] vines. The above differences in shoot

growth parameters, leaf area, and leaf dry weight between DC] and 3Cl vines in

 

60

Table 8. Influence of leaf removal and cropping level on shoot grouth parameters, leaf area, and
specific leaf ueidlt of potted Seyval grapevines (HRC 1989 - Experiment I).

 

 

Total shoot Ho. of Internode Total leaf Single Specific
Treatment’ length/vine nodes] vine length area [vine leaf area leaf ugight
(cm) (cm) (on?) lcm’) (Ila/cm )
Leaf removal
c 305.2 65.8 4.5 5035.5 82.1 7.80
R 290.9 63.2 4.5 4661.3 88.2 7.05
ns' ns ns ns ns ns
Crop. level
OCl 384.1a 73.6a 5.2a 6044.8a 97.3a 7.85
3Cl 227.819 56.9b 3.9b 3853.81: 76.1b 7.01
m it t” i t "8
Interaction ns ns ns ns ns ns

 

‘c:control (no leaves removed); R:leaves removed on Aug. 31/89 (near veraison)

00l:0 clusters per vine; 3Cl: 3 clusters per vine
'ns *, ", ”1' Hon significant or significant at 5%, 1X or 0.1% level, respectively.

Table 9. Influence of leaf removal and cropping level on shoot growth parameters, leaf area, and
specific leaf ueidlt of potted Seyval grapevines (HRC 1990 - Experiment II).

 

 

Total shoot Ho. of Internode Diameter Total leaf Single Specific
Treatment’ length/vine nodes] length of 5" area/vine leaf leaf
(cm) vine (can) intemodc (m2) area Heiaht
(an) (cm’) tuna/m2)
Leaf removal
C 198.3 52.1 3.8 5.8 3292.3 65.7 6.42
R1 223.2 56.1 3.9 5.5 3624.7 75.1 6.29
R2 208.3 54.0 3.8 5.5 3425.8 75.8 6.37
ns' ns ns ns ns ns ns
Crop. level
00l 247.3a 59.3a 4.1a 6.2a 4100.4a 78.7a 6.37
301 172.61: 48.91: 3.5b 5.0b 2805.4b 65.9b 6.34
m m m m it 9* m
Interaction ns ns ns ns ns ns ns

 

'C:control (no leaves removed); R1:leaves removed on July 27/90 (pea size); R2:leaves removed on

Aug.21/90 (veraison)
OCl:0 clusters per vine; 3Cl: 3 clusters per vine
'ns, *, **, 1"” Hon significant or significant at 5%, 1% or 0.1% level, respectively.

 

 

61

Table 10. Influence of leaf raoval and cropping level in 1990 on the dry weight partitioning of potted
Seyval grapevines at the end of the season (Septedaer 30/90) (Experiment 11).

 

 

 

 

Dry weight (g) Total Percent of total dry weight
Treatment’ dry
Fruits Leaves Canes Trmk Roots :39." Fruits Leaves Canes Tru'lk Roots
Leaf removal
c 31.8 24.6 26.3 13.8 41.8 138.2 21.7 17.8 19.1 10.9 30.5
R1 32.2 28.2 31.4 14.3 42.2 148.4 22.4 18.9 20.7 9.8 28.2
R2 28.6 22.6 25.0 15.6 38.0 129.7 23.4 17.1 18.4 12.2 28.8
ns' ns ns ns ns ns ns ns ns ns ns
Crop. level
001 0b 31.1a 42.1a 16.0a 50.8a 139.9 0b 22.1a 29.6a 12.1 36.1a
301 61.7a 19.1b 13.1b 13.1b 30.5b 137.6 45.0a 13.8b 9.1b 9.9 22.2b
m u m t ea "8 m m m "3 m
Interaction ns ns ns ns ns ns ns ns ns ns ns

 

’0:control (no leaves removed); R1:leaves removed on July 27/90 (pea size); R2:leaves removed on
Aug.21/90 (veraison)

001:0 clusters per vine; 301: 3 clusters per vine

'ns, *, *‘, 1'“ Hon significant or significant at 5%, 1% or 0.1% level, respectively.

Table 11. Influence of leaf removal and cropping level in the 1990 season on the dry weight of canes,
trunk and roots of potted Seyval grapevines, on average across partitioning dates in the fall and
winter of 1990/91 (Experiment II).

 

 

 

 

Treatment’ Dry weiM)
Canes Trmk Roots Total of the
three vine parts
Leaf removal: 0 34.5 13.2 42.8 90.5
R1 30.8 14.2 38.1 83.9
R2 29.3 14.1 36.3 79.7
ns' ns ns ns
Crap. level: 001 45.8a 15.1a 48.0a 108.9a
301 17.3b 12.5b 30.2b 59.91)
m ti on m
Interaction ns ns ns ns

 

’C:control (no leaves removed); R1:leaves removed on July 27/90 (pea size); R2:leaves removed on
Aus-21/90 (veraison)

'001:B clusters per vine; 301: 3 clusters per vine

“3a . *‘, *1" Hon significant or significant at 5%, 1X or 0.1% level, respectively.

 

 

 

62

Experiment 11 were consistent with the results obtained in Experiment I (Table 8).

H _ l E l l I . S I.

Of the vine tissues analyzed (Tables 12, 13 and 14), the roots had the highest
concentration of soluble carbohydrates and starch and, consequently, of total non-
structural carbohydrates (TNC) at any partitioning date; canes had higher soluble
carbohydrate concentration than the trunk, while the trunk had higher starch and
TNC concentration.

Regardless of the vine tissue, treatment, and basis of evaluation (dry weight
or volume), the soluble carbohydrate content had a sharp increase from September
30 to January 10, followed by a much smoother reduction from January to March.
The changes in soluble carbohydrate between sampling dates were proportionally
larger in the trunk and canes than in the roots. In canes (Table 12) and trunk (Table
13), the ﬂuctuations in starch content were opposite to those in soluble
carbohydrates. In roots, however, starch levels decreased not only from September
30 to January 10 but also from January 10 to March 14 (Table 14).

Leaf removal had no signiﬁcant effect on cane carbohydrate levels on
September 30 and January 10 (Table 12). In March, the leaf removal x cropping level
interaction was signiﬁcant for cane soluble carbohydrate and TNC expressed on a dry
weight basis. If only 3Cl vines are considered, the vines defoliated at veraison had
lower levels of these carbohydrates than the vines that were either not defoliated or
defoliated at pea size; on 0C1 vines, though, higher levels were found on control than

on defoliated vines, regardless of the defoliation date (data not shown). Leaf removal

63

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66
had no signiﬁcant effect on starch, soluble carbohydrate and TNC levels in roots and

trunk at any partitioning date (Tables 13 and 14). When all sampling dates were
considered, though, the R1 vines had higher root starch content than the R2 vines,
and higher root TNC than either C or R2 vines.

Cropping level effects on carbohydrate levels varied markedly with sampling
date and vine tissue. In canes, the cropping effect was only signiﬁcant on September
30, 1.5 weeks after harvest (Table 12). At this time, we, as well as trunk (Table 13)
soluble carbohydrate content on a dry weight basis were higher on 3Cl than on DC]
vines, in contrast with cane starch both on a dry weight and on a volume basis, and
cane TNC per unit of volume. Across sampling dates, the canes of 3Cl vines had
lower starch and TNC than those of OCl vines, on a volume basis (Table 12); by
contrast, the concentration of starch and TNC in the trunk (Table 13) and of starch
in roots (Table 14) were higher on 3Cl vines. Cropping had no signiﬁcant effect on
soluble carbohydrate and TNC levels in roots (Table 14). In mid-winter, the root
soluble carbohydrate content was higher on DC] than on 3Cl vines but only for non-

defoliated (C) vines (data not shown).

Discussion

12:1- {mun Lu. mm ° .A'V‘ Eff-v . 0 -.. lie-.1: 1.1! hlnm
C 1n 1' .1 l 1 [E ..
In Experiments I and II, in which gas exchange measurements were taken

relatively often, the course of the net CO2 assimilation rate per unit of leaf area (A)

67

throughout the growing season and some differences in A among leaf positions
reﬂect, in part, the aging effect reported in grapevines (Kriedemann, 1968,
Kriedemann :1 31., 1970) and other species (Flore and Lakso, 1989). Environmental
factors, and changes in sink activity and proximity to a carbon source, among other
factors (Flore and Lakso, 1989) also conceivably contributed to the results found.

In grapevine leaves, A increased as the leaf expanded, achieved a maximum
with full expansion, and declined later, toward senescence (Kriedemann, 1968,
Kriedemann :1 al. , 1970). In the present study, higher A values were initially found
at BAS or MID leaves but, as the season progressed, the AP or the MID leaves (in
1989 and 1990, respectively) became the most active. In 1989 (Tables 1 and 4), as in
the study of Edson (1991), the AP leaves became dominant, while in 1990 (Tables
2 and 5), as in Chaves (1984), A increased from the BAS to the MID leaf and then
decreased to the AP leaf. The difference between years is probably due to the fact
that in 1989, as in Edson (1991), the AP leaves measured were fully expanded, while
in 1990, like in Chaves (1984) they had not yet reached that stage.

Leaf aging was conceivably greatly responsible for the decline in A towards
the end of the season. The rate of development of new leaves decreased late in the
season; therefore, even though the position of the MID and AP leaves measured
evolved with shoot elongation, these leaves were successively older, like the BAS
ones. This is consistent with the decline in total leaf chlorophyll content and
chlorophyll a/b ratio from veraison to harvest (Table 7). Ribulose- l ,S-bisphosphate
carboxylase activity has been reported to decrease with leaf aging (Zima and Sesték,

1985). Besides, given the hypothesis of photosynthesis regulation by sink activity

 

68
(Neales and Incoll, 1968; Geiger, 1976), it ean also be suggested that decreased

daylength late in the season restricted the vegetative growth, which lowered the
photosynthetic demand and ampliﬁed the decline in the photosynthetic rate
associated with leaf aging (Kriedemann, 1977).

In Experiment 11 (Table 2), leaf removal at pea size (ﬁve weeks after full
bloom) presumably created a source limitation despite the reduced number of leaves
removed. The higher A at BAS and MID leaves on defoliated (R1) relative to
control (C) vines might have represented a compensatory response; E and g, were
likewise higher on Rl than on C vines (Appendix A). Increased A, g,, and E in
response to leaf removal has been previously reported (Hunter and Visser, 1988;
Candolﬁ-Vasconcelos, 1990). By contrast, no signiﬁcant effect on A, g,, and E was
observed here following leaf removal at or shortly after veraison on potted
(Experiment I) or on mature vines (Experiment III); if an effect occurred it could
have been limited to a short period following treatment, before the ﬁrst post-leaf
removal assessment. Although on potted vines the same number of leaves was
removed either at pea size or shortly after veraison, the leaves removed on the latter
date were proportionally less important due to the larger area available at this time
of the season. Differences in leaf physiological stage at the time of treatment
conceivably inﬂuenced the intensity of the photosynthetic response to the source/ sink
manipulation. In Experiment 11, the MID leaves were the most responsive to leaf
removal. The BAS, leaves were closer to the leaves removed but could not react as
intensively as the MID leaves presumably because they were older. By contrast, the

AP leaves had probably not fully developed the mechanisms to sense or to react to

 

69

the leaf removal stimulus or, beeause these leaves were further away from the
defoliation zone, they might have received a weaker ‘signal’ . In Experiment I, where
leaf removal was imposed near veraison, the BAS and MID leaves had probably
already passed the stage when they could adjust the photosynthetic apparatus to an
increased demand, hence the absence of a signiﬁcant response in A. WUE has been
reported to increase following leaf removal (Hunter and Visser, 1988; Candolﬁ-
Vasconcelos, 1990). This effect was only sporadieally found here, in Experiments I
and III (Appendix A).

In the experiments conducted, the enhancement of A due to the presence of
fruits is consistent with previous studies on grapevines (Loveys and Kriedemann,
1974; Kriedemann :1; a1., 1975; Kriedemann, 1977; Chaves, 1984; Downton et 31.,
1987) and several fruit crops (Flore and Lakso, 1989). Hale and Weaver (1962)
observed that early in the post-bloom period the clusters are relatively weak sinks,
and they become very powerful sinks only after fruit set. This may explain the ﬁnding
that, when the leaf positions were considered, the presence of fruits increased A at
3.5 weeks after full bloom in Experiment 11 (Table 5) but had no signiﬁcant in
Experiment I either at two days (data not shown) or at two weeks after full bloom
(Table 4). It can be argued that A remained higher on fruiting vines due to high
photosynthate demand and translocation toward the fruits, which would prevent or
minimize a hypothesized end-product inhibition of photosynthesis (Neales and Incoll,
1968). Hormonal control is also a possibility, as suggested by studies where the
decline in A following fruit removal was accompanied by a raise in phaseic acid and

abscisic acid (ABA) in leaves (Loveys and Kriedemann, 1974), and by a reduction

 

70
in gibberellin levels (Hoad at al, 1977). ABA has been implicated in the reduction

of stomatal conductance (Loveys and Kriedemann, 1974; Downton et a1. , 1988), and
gibberellin levels were found to be positively correlated to the activity of ribulose-l ,5-
bisphosphate carboxylase (Trehame and Stoddart, 1968).

Reduced light levels may lead to a lack of photosynthetic enhancement in
response to increased sink strength (Flore and Lakso, 1989). However, in another
experiment with potted vines conducted under the same conditions of Experiment II
except that cropping level was combined with vine shading to 24% of sunlight, a
signiﬁcant increase in A due to the presence of fruits was likewise observed
(Appendix B). It seems, therefore that a stronger light reduction than that imposed
would be needed to prevent the fruit effect on A from occurring on grapevine leaves.

On mature vines (Tables 3 and 6), the response of A to the presence of fruits
was noticeably lower than on young potted vines. In a previous study with ﬁeld grown
grapevines, no signiﬁcant differences in A were found between fruiting and non—
fruiting vines (Williams, 1986). Similarly, Kriedemann (1977) mentioned that the
photosynthetic adjustment to fruiting demands is more evident on small potted vines,
where shoot growth (therefore leaf number) is limited. In the experiments with
potted vines (Experiments Iand II), removal of all the lateral shoots likely enhanced
the cropping effect on A, by intensifying the photosynthate demand to the main
source leaves. Predictable differences in water status and in carbohydrate
accumulation between potted and ﬁeld vines may have also accounted for a different
degree of photosynthetic response to leaf removal and cropping level. On mature

vines, the fmit effect on A was particularly evident at the assessment three weeks

71
after veraison (Tables 3 and 6), probably reﬂecting a high photosynthate demand for

fruit ripening. On other occasions, this effect was probably masked due to
competitive vegetative sinks (Flore and Lakso, 1989). The intense vegetative growth
of the mature non-fruiting vines might have created a photosynthate demand similar
to that associated with the presence of fruits on 1.5 and NT vines.

A hypothetieal relationship between photosynthetic rate and chlorophyll level
has been investigated but conﬂicting results have been reported (Buttery and Buzzell,
1977; Hunter and Visser, 1989). In this study, as in Hunter and Visser (1989), there
were situations where such a relationship apparently occurred, but this was not a
general rule. At the gas exchange measurements between chlorophyll assessments in
Experiment 11 (August 29 and September 13), A was higher on 3Cl than on 0C1 vines
at every leaf position (Table 2). This was in correspondence to higher chlorophyll
levels at MID and AP leaves on the former vines (Table 7). However, at BAS leaves,
where the fruit effect on A was more strongly marked, the chlorophyll levels were
not signiﬁcantly higher on 3Cl than on OCl vines. This suggests that differences in
leaf chlorophyll concentration were not decisive for the enhanced A on fruiting vines.
Chlorophyll levels were found to increase in response to defoliation (Hofacker, 1978;
Hunter and Visser, 1989; Candolﬁ-Vasconcelos, 1990). Probably due to the reduced
number of leaves removed, no clear leaf removal effect on total leaf chlorophyll was

noticed in this study.

 

{2”- 1.‘nor-.. .H l'J'J'J' ." I'vl. H V'°‘t:!‘ 0 J 14' Dan-.1;

 

Although either one or both source! sink manipulation treatments imposed
had a signiﬁcant effect on the net C02 assimilation rate per unit of leaf area (A), it
must be noted that this rate may not be well correlated with that of the vine as a
whole (Edson, 1991), nor with total dry matter production (Kramer, 1981). At
individual leaves, A responded positively to an increased cropping level, but there
was no signiﬁcant correlation between cropping and net C02 assimilation rate of the
whole vine; the lower A on slightly cropped vines appeared to be compensated for
by a larger leaf area (Edson, 1991). In the present study, the CO, assimilation of the
whole vine was not evaluated, but the absence of a signiﬁcant cropping effect on
total dry matter accumulation (Table 10) may indicate a lack of photosynthetic
response at the whole vine level. This suggestion must be viewed with caution,
though, given that the overall dry matter accumulation resulted from assimilate
production and utilization over an extended period; besides, a similar total dry weight
may reﬂect a different photosynthate production, due to differences both in dry
matter partitioning, and in the respiration rate (Amthor, 1989) and energy content
per unit of dry weight (Gifford et al., 1984) of the different plant parts.

The lack of a signiﬁcant cropping effect on total dry weight (Table 10) is
consistent with the ﬁndings of Eibach and Alleweldt (1985) and Edson (1991); in
both studies, as in the present one, cropping level had a marked inﬂuence, however,
on dry matter partitioning. Similar results were reported by Lenz (1979) in citrus.

Assimilates were allocated into the fruits at the expense of canes, roots and leaves

73
(Tables 10 and 11), in agreement with the generalized observation that fruits are

successful competitive sinks (Wardlaw, 1968).

The vines partitioned on September 30/90 were still holding functional leaves,
while those partitioned in January and March of 1991 had their leaves naturally
abscised and carbohydrate accumulation proceeded normally. This may explain the
observation that in eanes (Table 12) and roots (Table 14) the levels of TNC were
higher on January 10 than on September 30, despite the consumption of reserves in
maintenance processes that occurred meanwhile. Respiratory losses most certainly
accounted for the decrease in TNC from January and March. The observed high
concentration of storage carbohydrates in roots is consistent with previous results
(Schrader, 1924; Winkler and Williams, 1945). Cell walls are proportionally more
developed in stem than in root tissues; this would lead to a higher concentration of
non-structural earbohydrates in roots even if the cell content were similar in both
tissues (Winkler and Williams, 1945). Even though carbohydrate accumulation was
not completed on September 30, the fact that starch was the most abundant non-
structural carbohydrate in all the tissues analyzed and that its concentration largely
changed during the dormant season agrees with previous studies with grapevines
where starch was found to be the main storage carbohydrate (Richey and Bowers,
1924; Winkler and Williams, 1945). In this study, the number of sampling dates does
not allow for a detailed description of carbohydrate evolution. Nevertheless, the
increase in soluble carbohydrates between September 30/90 and January 10/91 and
the concomitant reduction in starch (Tables 12, 13 and 14) seem to agree with

previous reports of a starchzsugar conversion during the fall and in early to mid-

74
winter, in grapevines (Richey and Bowers, 1924; Schrader, 1924; Winkler and

Williams, 1945) and several other species (Siminovitch et a1., 1953; Levitt, 1956). This
conversion appeared to occur in all vine tissues analyzed. In the trunk, where the
TNC levels changed only slightly between September 30 and January 10 (unlike in
canes and roots), the evidence of a starch:sugar conversion is particularly suggestive;
the increase of 111.5 mg/ g dry weight in soluble carbohydrate content between these
dates closely approached the decrease in starch concentration (Table 13). The
increase in starch and decrease in soluble carbohydrates noticed in canes (Table 12)
and trunk (Table 13) between January and March of 1991 is consistent with the
suggestion of a sugar: starch conversion in the late winter, before the above-ground
growth starts (Schrader, 1924; Kliewer, 1967). In roots, however, starch decreased
again between January and March (Table 14). This was probably due to larger
respirational losses in the roots in late winter due to higher soil than air temperature,
and root growth (Winkler and Williams, 1945).

The reduced leaf removal effect on the carbohydrate content of the tissues
analyzed is conceivably due to the low number of leaves removed. In the few cases
when the leaf removal effect was signiﬁcant (root starch and TNC levels averaged
across sampling dates) the vines defoliated at pea size (R1) had higher carbohydrate
levels than those defoliated at veraison (R2), and similar or even higher (in the case
of root TNC) levels than the control vines. In March, cane soluble carbohydrate and
TNC on a dry weight basis were higher in R1 than in R2 vines in the case of 3Cl
vines; when only 0C1 vines were considered, levels were lower on R1 and R2 than

on control vines. It appears that the presence of fruits during the treatment season

 

 

 

75

was needed for a carbohydrate compensation to occur in canes of R1 vines.
Carbohydrate translocation might have been altered by leaf removal at pea size,
unlike by removal at veraison; this hypothesis needs further investigation. Besides,
the enhancement of A at BAS and MID leaves in response to leaf removal at pea
size has probably contributed to attenuate the leaf removal effects on carbohydrate
levels.

Several reasons may have contributed to the variation in cropping effects on
earbohydrate levels among sampling dates and vine tissues. On September 30, 1.5
weeks after harvest, the canes of SC] vines had lower starch concentration than those
of 0C1 vines (Table 12), conceivably because they had been deprived of
carbohydrates for the beneﬁt of the clusters, the dominant sink after berry set (Hale
and Weaver, 1962). Besides photosynthates translocated from the leaves, the ripening
berries may import sugars derived from carbohydrate reserves in shoots (Matsui gt
3.1., 1979), or shoots, roots and trunk (Mansﬁeld and Howell, 1981). Following
harvest, carbohydrate allocation to storage tissues was conceivably greatly enhanced
on 3Cl vines, while until then carbohydrates were mainly diverted towards the
clusters. Limitations in the capacity of the vascular system to adjust to the altered
translocation pattern may explain the ﬁnding that on September 30 the levels of
soluble carbohydrates in canes (Table 12) and trunk (Table 13) were higher, on a dry
weight basis, on 3Cl than on 0C1 vines. Moreover, the wood/bark ratio was
conceivably lower in canes of 3Cl than of 0C1 vines due to the smaller diameter of
the former canes (Table 9); this may have further contributed to the lower starch and

higher soluble carbohydrate content in the canes of 3C1 vines. Indeed, Winkler and

76
Williams (1945) found that starch concentration was higher in the wood than in the

bark of basal eane portions, while Kliewer (1967) noticed that the soluble
carbohydrate content in the early fall was higher in the shoot bark than in the wood.
In spite of the large amount of photosynthate diverted to the clusters, 3Cl vines had
higher starch concentration in the trunk (Table 13) and roots (Table 14) than 0C1
vines. The physieal constraint created by the smaller size of the root system and
trunk of 3C1 vines (Table 9), and lower respirational losses in these vines to meet
maintenance needs during the dormant season, are possible explanations for the

above results.

Conclusions

Basal leaf removal at pea size (ﬁve weeks after full bloom) increased the leaf
net CO, assimilation rate (A) at basal and middle-shoot leaf positions on potted
vines, while removal at veraison had no signiﬁcant effect on A, whether on potted
or on mature ﬁeld vines. As in previous studies with grapevines and other crops, the
presence of fruits increased A at individual leaves. This effect was more clearly
evidenced on young potted than on mature ﬁeld vines. The observed changes in A
are likely due to an inﬂuence of the source/sink manipulative treatments on the
photosynthate demand at individual leaves. Fruiting and non-fruiting potted vines had
a similar total dry weight, a coarse indication that cropping level had probably little
inﬂuence on the net photosynthesis of the vine as a whole. The presence of fruits

had, on the other hand, a marked effect on dry matter allocation; the fruits

 

77
developed at the expense of all the vegetative components.

Fruit development increased, on a dry weight basis, the soluble earbohydrate
content in canes and trunk of potted vines in the early fall (1.5 weeks after harvest),
but decreased the starch and total non-structural carbohydrate (TNC) in canes (on
a fresh volume basis) when the early fall, mid—, and late winter data were combined.
On the other hand, the concentration of starch and TNC in the trunk and of starch
in roots were higher on the vines that had borne fruit, conceivably due to decreased
storage capacity associated with the lower vegetative development of these vines.
Basal leaf removal had no signiﬁcant effect on growth, total dry weight and dry
matter partitioning in potted vines, and little inﬂuence on carbohydrate concentration
in the tissues analyzed. In the few instances when a signiﬁcant effect was found,
carbohydrate concentration was favored by leaf removal at pea size relative to leaf
removal at veraison. The observed enhancement of A following leaf removal at pea
size and, probably an alteration in translocation pattern, may have contributed to the
above results. Probable implications of these ﬁndings on the cold hardiness of bud

and cane tissues and on bud fruitfulness will be discussed in further chapters.

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82

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CHAPTER II

Inﬂuence of Basal Leaf Removal and Cropping Level on the Cold Hardiness of

Primary Bud and Cane Tissues of Seyval Grapevines

83

Abstract

On potted vines, basal leaf removal in 1990 had no signiﬁcant effect on
primary bud and cane hardiness in the 1990/91 dormant season. Hardiness was
higher on fruiting than on non-fruiting vines, supposedly due to improved acclimation
of the former vines, resulting from less vigorous growth.

On mature vines, treatment effects on hardiness were more marked in
1989/90 than in 1990/91. Carbohydrate storage in the 1989 fall was probably
impaired due to an early leaf killing frost and, in fruiting vines, to a heavy 1989 crop.
Basal leaf removal 2.5 weeks after veraison in 1989 decreased cane hardiness when
all sampling dates of 1989/90 were considered; removal at veraison in 1990 had no
signiﬁcant effect on tissue hardiness in 1990/91. Leaf removal had no signiﬁcant
effect on the number of canes with ﬁve or more mature nodes before pruning in the
following April, but reduced the number and percentage of canes with less than ﬁve
mature nodes. The percentage of shootless nodes was not signiﬁcantly affected by
leaf removal in the previous season. Cropping level affected primary bud hardiness
when the sampling dates in the 1989/90 dormant season were combined. Non-fruiting
(0) vines had hardier buds than unthinned (NT) ones; vines thinned to 1.5
clusters/node retained (1.5) had intermediate bud hardiness. The percentage of
shootless nodes in 1990 was accordingly affected by cropping level. In 1990/91, an
overall difference of 1°C separated the primary bud hardiness of fruiting and non-
fruiting vines; this difference was not signiﬁcant but appeared to be viticulturally

relevant, given the higher percentage of shootless nodes on the former vines in 1991.

 

85

The number of canes with ﬁve or more mature nodes before pruning was higher on
non-fruiting than on fruiting vines, but the percentage relative to the total number
of canes/vine did not signiﬁcantly differ among cropping levels. There were no
signiﬁcant differences in hardiness, cane maturity and percentage of shootless nodes

between 1.5 and NT vines in any of the trial years.
Introduction

Winter cold is a serious problem of the grape industry at (but not limited to)
the northern limits of culture (W olpert and Howell, 1985). In Northeastern
Viticultural areas of the U.S.A. cold injury is a major concern (Dethier and Shaulis,
1964; Shaulis et a1., 1968; Howell and Shaulis, 1980) and has motivated an intense
effort to determine the factors that inﬂuence cold resistance, and to evaluate the
impact of diverse cultural practices on grapevine hardiness (Stergios and Howell,
1977; Byme and Howell, 1978; Howell e]; a, 1978; Howell and Shaulis, 1980;
Mansﬁeld and Howell, 1981; Wolpert and Howell, 1985; Howell, 1988; Miller at 3.,
1988).

The dormant season can be subdivided into distinct periods characterized by
differences in environmental conditions and in the expression of hardiness (Howell,
1988). The ﬁrst period is acclimation, or the transition from the non-hardy to the
hardy condition. The second period, mid-winter, is the time when cold is most severe
and the vines exhibit the maximum hardiness (Miillner and Mayer, 1978; Howell,

1988). The third is a post-rest period, in which cold hardiness ﬂuctuates in response

86
to ﬂuctuating temperatures. This is followed by a period of gradual warming when

deacclimation takes place (Howell, 1988).

The internal mechanisms responsible for the above changes in hardiness are
not well understood. ‘Several thousand’ papers have been written on cold hardiness
and freezing injury (Steponkus and Wiest, 1978). Nevertheless, given the complexity
of the processes involved in cold acclimation, freezing injury or recovery from injury,
a general theory to explain these phenomena has not been found. A large number
of metabolic and physiological changes accompanying cold acclimation have been
investigated for possible involvement in the hardening processes. These include
qualitative and quantitative changes in cellular compounds such as carbohydrates,
lipids, nucleic acids, proteins, and growth regulators, namely ABA (for a review see
Levitt, 1980; Guy, 1990). It still remains to be clariﬁed, though, whether correlations
rather than cause-effect relationships may link those changes and the hardiness
responses.

Carbohydrates have been suggested to play an osmotic role in hardiness
(Levitt, 1956), act as cryoprotectants, or as source of energy for hardening processes
(Howell and Stackhouse, 1973). Whichever their actual role is, a reduced
carbohydrate storage resulting from defoliation treatments was considered
detrimental to tissue hardiness and winter survival in grapevines (Howell et a1. , 1978;
Mansﬁeld and Howell, 1981; Howell, 1988) and sour cherry (Howell and Stackhouse,
1973).

Previous research conducted in our laboratory to evaluate the inﬂuence of

defoliation on grapevine hardiness utilized a severe defoliation stress: removing 100%

87
(Stergios and Howell, 1977; Howell et 31., 1978) and either 100% or 50% of the

leaves (Mansﬁeld and Howell, 1981). In the current study, fruiting and non-fruiting
vines were subjected to the removal of only a few basal leaves in the cluster region
(or equivalent in non-fruiting vines) and the effects of cropping level and leaf
removal on cane maturity and on the hardiness of cane and primary bud tissues
taken from the defoliated region were investigated. This study may represent a step
towards the evaluation of the applicability of basal leaf removal in a region like
Michigan, where cold hardiness is crucial for a successful grape growing. If, as
suggested by Hale and Weaver ( 1962) and Smart et al. (1982), the leaf subtending
a bud is the main photosynthate source for that bud, it might be anticipated that the
buds axillary to the leaves removed are affected in their carbohydrate status and cold
resistance, unless there is some mechanism to attenuate or compensate for a
localized carbohydrate depletion, or the carbohydrate levels are simply not limiting

the hardening processes.

Materials and Methods

Pl . l l 1' !
Experiment I

Own-rooted, mature, bearing Seyval (Seyve-Villard 5-276) grapevines in a
vineyard at the Clarksville Horticultural Experimental Station (CHES), Clarksville,
Michigan, were used in this experiment. The vineyard was planted in 1983 in a

Kalamazoo sandy loam soil, with a spacing of 2.4m x3.0m within and between rows,

88

and a N-S row orientation. The vines were trained to Hudson River Umbrella (a
bilateral cordon at the top wire), with the top wire at 1.8 m height. The vines were
balanced pruned using a 15+10 pruning formula (Reynolds et a” 1986), up to a
maximum of 65 nodes retained per vine. Other details regarding vineyard
maintenance were presented in Chapter 1.

Prior to the 1989 growing season, a randomized block design was established.
Vine size (weight of one-year old cane prunings), which varied between 1.0 and 1.5
kg, was used as the blocking variable. Five blocks of six vines were deﬁned, one vine
per treatment combination. Treatments were arranged as a 2x3 factorial with leaf
removal and cropping level as factors. The leaf removal levels were: C = no leaves
nor lateral shoots removed (control); R = main leaves and lateral shoots removed
at three consecutive basal nodes on all the shoots of the vine. The cropping levels
were: 0 = 0 clusters per vine; 1.5 = 1.5 clusters per node retained at pruning; NT
= all clusters left (no thinning). The treatment combinations are abbreviated as C/0,
C/1.5, C/NT, RIO, R/1.5, and R/NT. In the 1990 growing season each vine received
the same treatment combination assigned in 1989. Cluster thinning was done on June
12/1989 (one week before full bloom) and June 27/1990 (nine days after full bloom).
Leaf removal was imposed on September 10/1989 (2.5 weeks after veraison) and
August 15/1990 (veraison). On fruiting shoots, leaves and lateral shoots opposite, one
node above, and one node below the basal cluster were removed. On non-fruiting
shoots, leaves and laterals were removed from equivalent node positions. The
position of the defoliated nodes was marked on the shoots for further reference.

Lateral shoots were allowed to develop normally except for those at the three treated

89

nodes on the defoliated vines.

Experiment 11

This experiment was initiated in 1990 at the Horticultural Research Center
(HRC), East Lansing, Michigan, at the same site and simultaneously with another
leaf removal experiment in potted vines described in a previous chapter (Experiment
11, Chapter I). The installation procedure, cultural practices (training, removal of
lateral shoots, irrigation, fertilization and spraying) and the treatments imposed were
exactly the same and performed on the same dates in both experiments.

In May/1990 two-year-old own-rooted Seyval grapevines were weighed and
planted in 19 1 pots containing a sterilized loam, sand and peat mixture with good
water holding and aeration properties. Nine blocks of six vines each were used in this
experiment; vine fresh weight before planting was used as the blocking variable. The
potted vines were placed on a ﬂat gravel-covered area at a 1.0 m x 1.2 m spacing,
allowing for good light exposure, and trained to two shoots. Treatments were
arranged in a 3x2factorial, with leaf removal and cropping level as factors. The leaf
removal levels used were: C = no main leaves removed (control); R1 = main leaves
removed at three consecutive basal nodes at pea size (July 27, ﬁve weeks after full
bloom); R2 = main leaves removed at three consecutive basal nodes at veraison
(Aug. 21, eight weeks after full bloom). The cropping level was either 0C1 = 0
clusters per vine or 3Cl = 3 clusters per vine. Treatment combinations are
abbreviated as C/0Cl, C/3Cl, R1/0Cl, R1/3Cl, R2/0Cl, and R2/3Cl.

Thinning was imposed on July 4 (10 days after full bloom). On the vines

 

w— __ “w' .._—‘ .

 

90

thinned to 3 clusters, the basal cluster on one shoot and two clusters (the basal and
the second) on the other shoot were retained. Leaves were removed on both vine
shoots at the three node positions indieated for mature ﬁeld vines (Experiment I).
Unlike Experiment I, all the lateral shoots were removed at weekly intervals,
regardless of the treatment combination. This was done to avoid the variability that
would result from an erratic lateral growth (Buttrose, 1968).

During the 1990/91 dormant season, the vines were kept outdoors mulched

with straw up to most of the trunk height.

WW
Experiment I

Canes were collected at three occasions during the 1989/90 and 1990/91
dormant seasons: late fall, mid-winter, and early spring before bud-burst. Cane
sampling considered the factors known to inﬂuence cold hardiness, as reported by
Howell and Shaulis (1980). Well exposed canes with dark periderm and a medium
diameter (7-10 mm, averaged over two perpendicular directions between nodes four
and ﬁve) were collected at all sampling dates. On the third sampling date of 1990/91
(March 26/91), the non-thinned vines were not sampled, due to insufﬁcient number
of canes with the desired characteristics. The canes removed from each vine were
weighed so that, at pruning in 1990 and 1991, the vine size was obtained by adding
the weight of the cane prunings from each vine to the weight of the canes removed
from that vine for cold hardiness assessments in the previous dormant season.

Only the cane segments containing the three nodes subjected to leaf removal

 

 

91

in the previous season (or equivalent nodes in the case of the non-defoliated vines)
were used in the freezing tests. These segments were put in plastic bags, kept in
Styrofoam containers with ice during transport to the laboratory, and then stored at

0°C until being used in the freezing runs within 24 hours.

Experiment II

Canes were sampled during the 1990/91 dormant season, at the same
occasions as in Experiment I. The nine blocks of vines were distributed into three
groups (lighter, medium and heavier) according to the initial fresh weight of the
vines. One block per group was randomly selected to be used at each sampling date.
Both canes of each vine were sampled regardless of their diameter. All canes were
well exposed and dark, but canes from fruiting (3C1) vines had smaller diameters
than those from non-fruiting (0C1) ones (data not shown). Three-node cane segments

were taken from the same cane position selected in Experiment 1.

MW

Controlled freezing tests were conducted to evaluate the cold hardiness of
cane and primary bud tissues. Sample preparation was based on the procedure
described by Howell and Weiser (1970) and Howell et a1. (1978).

The three-node cane segments were cut into single node sections and the
sections from the vines subjected to the same treatment combination were pooled
together. Three single node sections per temperature per treatment combination

were used. The base of the single node cane sections was wrapped in moistened

92

cheese cloth to inoculate the tissues with ice and thereby reduce the degree of
supercooling during the freezing test (McKenzie and Weiser, 1975). To monitor the
progress of the freezing run, a thermocouple (26 gauge copper-constantan) was
inserted into the pith of a cane section in each set including all the treatment

combinations. The sets were then wrapped in aluminum foil. In 1989/90 they were
further placed in vacuum ﬂasks to promote a gradual decrease in tissue temperature.

Then they were placed in a Revco Ultra Low freezer where the temperature was
manually lowered to achieve a temperature decline of 3 to 5°C/ hour. In 1990/91 no
vacuum ﬂasks were considered necessary because a steady temperature decrease of
4.0°Clhour was automatically controlled using a computer program.

Five target freezing temperatures and a non-freezing one were used per
sampling date. The unfrozen tissues were held at 5°C during the freezing runs and
thereafter subjected to the same procedures as the frozen materials. Target
temperatures were separated by 3 or 4°C, depending on the time of sampling. The
temperature range used aimed at obtaining 100% of survival at the uppermost
temperature and 100% of tissue death at the lowest one.

The samples were removed from the freezer when the appropriate target
temperatures were attained and then allowed to gradually thaw at 2°C until the
following day. Then they were placed in aerated humid chambers at room
temperature (approx. 20°C). Ten days later the mortality of primary buds and cane
tissues was evaluated under a binocular microscope using the browning test (Howell
and Weiser, 1970; Stergios and Howell, 1973). Primary buds were considered dead

if the primordia were brown and water soaked; canes were rated as dead if the

93

cambium/phloem area was brown in most of its extension.

-.t- n.t' 4.3131 .atrn- . u..-- tux . 11.-.1 - ﬁ-cl I’

On April 13/90 and April 1/91, before pruning, each vine was evaluated for
the number of canes with ﬁve or more mature nodes. On April 1/91, after two
treatment seasons, the total number of eanes per vine and the number of canes with
ﬁve or more mature nodes and medium diameter (7- 10mm between nodes four and
ﬁve) were also assessed. These values were corrected by adding the number of canes
removed from each vine for cold hardiness assessments in the preceding dormant
season.

The percentage of shootless nodes was assessed in the early summer of 1990
(July 5) and 1991 (June 20), about two weeks after full bloom. It was assumed that
by this time all the shoots for the current season had emerged. This percentage was
ealculated by counting the number of nodes that failed to develop and dividing it by

the total number of buds retained at pruning.

S . . l l .
A modiﬁed Spearman-Karber equation (Bittenbender and Howell, 1974) was

used to estimate the temperature at which 50% mortality occurred (Tm). For as
of exposition, statistical signiﬁcance was indicated in the tables relative to the T5,0
values. However, the hardiness data analyzed were the discrete injury data for canes
and primary buds at the temperatures tested. The number of dead tissues at each

temperature for every treatment combination was converted to percentage and then

94

subjected to the arc-sine of the square root transformation. The transformed data
were then analyzed using the GLM (from General Linear Models) procedure of the
Statistical Analysis System package (SAS Institute Inc., 1985). Stressing temperature

was included in the model as a covariate. The analysis was done for each sampling
date of both seasons, as well as for the pooled data of the three sampling dates in
1989/90, for the ﬁrst two dates of 1990/91 (due to the unavailability of cane material
of the NT level of cropping at the third assessment), and for the three dates of
1990/91 (not considering the NT level in the calculations). When more than one
sampling date was analyzed, sampling date was included in the model as a blocking
variable. Because stressing temperatures varied with sampling date, temperature was
considered nested within date.

Data on percentage of shootless nodes and percentage of canes per maturity
class were subjected to the arc-sine of the square root transformation and then
analyzed by analysis of variance.

In {ii the statistical analyses when the F-values were signiﬁcant at the 5 % or

lower level, mean separation was done using the LSD test at the 5 % level.

Results and Discussion

WWW
On mature, ﬁeld-grown vines, basal leaf removal (R) had a signiﬁcant effect

on cane hardiness in the mid-winter of 1989/90 and across that dormant season;

canes were hardier on control (C) than on R vines, as evidenced by lower T,o on the

95
former (Table 1). When the three sampling dates of 1989/90 were considered,

primary bud hardiness was lower on fruiting than on non-fruiting vines; the vines
thinned to 1.5 clusters per node retained (1.5 vines) had intermediate bud hardiness
between unthinned (NT) and non-fruiting (0) vines, not signiﬁcantly different from
any of the two.

In 1990/91 (Table 2), treatment effects on the hardiness of mature vines were,
in general, less marked than in 1989/90 (Table 1). Cane hardiness was not
signiﬁcantly affected by leaf removal neither was primary bud hardiness by cropping
level, unlike in 1989/90. On the other hand, canes were hardier on 1.5 than on non-
fruiting vines when all sampling dates of 1990/91 were considered, although no
signiﬁcant cropping effect was observed for individual sampling dates. Data were not
analyzed across years; however, cane and primary bud hardiness were clearly higher
in 1990/91 than in 1989/90 at comparable sampling dates, an exception being cane
hardiness in March (Tables 1 and 2; Figures 1 and 2).

On mature vines, leaf removal consisted of removing not only basal main
leaves but also lateral shoots (hence lateral leaves) at the defoliated nodes. During
the post-veraison period, the leaves on lateral shoots are a very active source of
assimilates not only for the ripening cluster but also for carbohydrate storage in the
wood (Candolﬁ-Vasconcelos, 1990). Under the conditions of Experiment I, the
possibility that some compensatory response might have attenuated the effects of leaf
removal is remote. In a study earlier presented (Chapter I), there was no signiﬁcant
enhancement of the CO2 assimilation rate following leaf removal at veraison. Besides,

based on Hunter and Visser (1990), a compensatory increase in lateral shoot growth

 

96

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98

Figure 1. Maximum-minimum temperature proﬁle for the 1989/90 dormant season
at the site of Experiment I (Clarksville) and the cold hardiness (1‘50) of primary bud
and cane tissues per cropping level x leaf removal treatment combination on mature
Seyval grapevines in the late fall, mid-winter and early spring of 1989/90 (sampling
dates indicated by arrows in the upper graph). Means per treatment level are
presented in Table 1.

Leaf removal:
0 control (no leaves removed)
C23 R: basal leaves removed on September 10/ 89

Cropping level (imposed on June 12/89):
0 : 0 clusters per vine
1.5: thinned to 1.5 clusters /node retained
NT: unthinned

 

 
 

 

 

 

 

 

 

 

 

 

 

 

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DEC. 1

 

 

 

 

 

 

 

 

100

Figure 2. Maximum-minimum temperature proﬁle for the 1990/91 dormant season
at the site of Experiment I (Clarksville)z and the cold hardiness (T50) of primary bud
and cane tissues per cropping x leaf removal treatment combination on mature
Seyval grapevines in the late fall, mid-winter and early spring of 1990/91 (samng
dates indicated by arrows in the upper graph). Means per treatment level are
presented in Table 2.

Leaf removal:
C: control (no leaves removed)
CUR: basal leaves removed on August 15/90

Cropping level (imposed on June 27/90):
0 : 0 clusters per vine
1.5 : thinned to 1.5 clusters Inode retained
NT: unthinned

‘Except for the period from Feb. 9 to Feb. 25 when data at Clarksville were not available and maximum
and minimum temperature were estimated by regression from the values at a nearby station (Grand Rapids).
The regression equations were ﬁtted considering the temperature at both sites in the 10—day period
immediately before and after the period of missing data. The equations used were: YBO.5003X + 10.518
(R’=0.843) for minimum temperature and Y= 0.7061X + 4.3309 (R2=O.9003) for maximum
temperature, where Y and X are the temperature (°F) at Clarksville and Grand Rapids, respectively.

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102

following leaf removal as late as veraison seems unlikely.

One possible reason for the differences in treatment effects between the
1989/90 and the 1990/91 dormant seasons is a heavier crop and stronger growth
inhibition in fruiting vines in 1989 than in 1990 (Chapter 111). Moreover, an
unseasonably early leaf killing frost in the fall of 1989 presumably affected
carbohydrate storage for the 1989/1990 dormant season aggravating, in fruiting vines,
the stress resulting from the heavy 1989 crop. The fact that primary bud hardiness
in 1989/90 was affected by the 1989 crop may be due to insufﬁcient carbohydrate
accumulation. Previous studies showed that cluster thinning, presumably by reducing
competition for earbohydrates, improved hardiness on heavily stressed vines (Howell
91 31., 1978; Howell, 1988). An inspection of the T50 means in 1989/90 for each
treatment combination (Figure 1) revealed that the mid-winter reduction in cane
hardiness by leaf removal in 1989 derived solely from the response of the fruiting (1.5
and NT) vines. The difference in T,0 values between C and R vines was as large as
8°C and 6.5°C for eanes of NT and of 1.5 vines, respectively; on fruiting vines, mid-
winter primary bud hardiness was also apparently affected by leaf removal although
to a lesser, non-signiﬁcant degree. The above results suggest that the activity of the
leaves removed from fruiting vines would otherwise have been particularly important
in 1989/90 because not only the heavy crop in 1989 but also the shorter season due
to early frost would have led to impaired carbohydrate accumulation. On the other
hand, the ﬁnding that in 1990/91 the only signiﬁcant treatment mean difference was
that of hardier canes on 1.5 than on 0 vines suggests that carbohydrate storage was

less critical for hardiness in 1990/91, following the 1990 season when fruiting vines

103
yielded a light crop and growth was relatively intense.

On potted vines, leaf removal in 1990 had no signiﬁcant effect on cane and
primary bud hardiness during the 1990/91 dormant season (Table 3). Fruiting (3Cl)
potted vines had hardier canes than non-fruiting (0C1) ones in the late fall of 1990
and in the early spring of 1991, as well as hardier primary bud and cane tissues when
the three sampling dates of 1990/91 were considered. Thus, cropping level effects on
hardiness were more marked on potted (Table 3) than on mature vines (Table 2)
during the same dormant season. Either on potted or on ﬁeld vines, dark, well
exposed canes were sampled for hardiness assessments. However, while the canes
from mature vines were selected for a deﬁned diameter range, those from potted
vines were not subjected to diameter selection and the canes sampled from BC] vines
had smaller diameter than those from DC] vines (data not shown). The lower vigor
of the canes from 3C1 vines conceivably allowed for a better maturation and
acclimation and hence for an increased cane and bud hardiness. On the other hand,
the use of cane diameter as a sampling criterion on mature ﬁeld vines, and the fact
that mature vines were balanced-pruned throughout this study probably attenuated
the treatment effects on cold hardiness (Howell and Shaulis, 1980; Wolpert and
Howell, 1985).

Changes in hardiness degree have often been found to correspond to
earbohydrate conversions (Guy, 1990). Sugar levels usually raise in the fall as plants
harden and decrease in spring with dehardening (Siminovitch et a1. , 1953; Levitt,
1956). In grapevine (Wample et al., 1988) and several other species (Sakai, 1960;

Layne and Ward, 1978; Raese et al, 1978; Levitt, 1980) a close relationship was

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105

noticed between sugar content and hardiness levels, but that was not true for other
studies (Steponkus and Lanphear, 1968; references in Levitt, 1980). These ﬁndings
can be resolved considering that cold acclimation is not solely due to an
accumulation of sugars, thus a direct parallelism between the levels of sugars and of
cold hardiness would occur only if sugar content was limiting the rate or degree of
acclimation (Steponkus and Lanphear, 1968).

In a study presented earlier (Chapter I), earbohydrate analyses (starch and
soluble carbohydrates) were done on potted vines grown under the same conditions
and subjected to the same treatments as those in Experiment 11. Internodal cane
samples were taken in the early fall, mid- and late winter of 1990/91 within the cane
region used in the hardiness determinations here presented. The sampling dates for
carbohydrate evaluation did not correspond to those for hardiness assessments during
the same dormant season, but still some inferences can be drawn by comparing the
results from both studies. In the early fall, cane soluble carbohydrate concentration
(in contrast with starch concentration) was higher on fruiting (3Cl) than on non-
fruiting (0C1) vines; no signiﬁcant differences were found in total non-structural
earbohydrate. Assuming that this relationship was valid throughout the fall, it can be
suggested that higher soluble carbohydrate levels may have contributed to hardier
cane tissues on 3Cl than on 0C1 vines at the ﬁrst hardiness assessment of 1990/91
(Table 3). On mature ﬁeld vines, by analogy with the potted ones, the relatively high
hardiness levels of cane and primary bud tissues on C/NT vines in the late fall of
1990 (Figure 2) could also be associated with a relatively high soluble carbohydrate

content in the eanes of these vines. In March/91, differences in cane hardiness

106
between 3Cl and 0C1 vines would not have been anticipated from carbohydrate

analyses (Table 12 of Chapter I). Indeed, only on R1 vines and solely for soluble
carbohydrate content was there in March a signiﬁcant difference between canes of
3Cl and 0C1 vines (higher levels in the former), while hardiness differences between
the two cropping levels were particularly marked for R2 and C vines (results not
shown). It can be suggested that cane carbohydrate content was probably not a
decisive factor for hardiness at this time of the 1990/91 season.

On mature ﬁeld vines, no carbohydrate analyses were done. However, as
previously discussed, carbohydrate content might have limited cold hardiness in
situations where carbohydrate insufﬁciency was more likely to occur, namely during
the 1989/90 dormant season. In contrast, there were instances where such possibility
appeared unlikely, such as in assessments where leaf removal apparently (though not
signiﬁcantly) improved cane and/or primary hardiness, in spite of the expectation
that eane carbohydrate levels would be affected (Figures 1 and 2). These include the
assessments in January/1990 for canes of non-fruiting (0) vines, in the fall of 1990
for 0 and 1.5 vines, in March/1990 for primary buds, and in March/1991 for both
canes and primary buds (Figures 1 and 2). In the late March assessments,
inconsistent hardiness results may in part be due to changeable hardiness levels due
to large ﬂuctuations in ambient temperature (Figures 1 and 2). The possibility also
exists that, at least in some of those situations other factors, perhaps hormonal in
nature, were more decisive to hardiness than carbohydrate levels.

Although some exceptions occur, growth inhibitors have been found to

promote and growth promoters to reduce hardiness levels. There is evidence

107
suggesting that ABA and gibberellin may be endogenous hardiness promoter and

inhibitor, respectively, but some contradictory results have been reported (Howell
and Dennis, 1981). Besides their antagonistic effects on growth, the fact that ABA
has been associated with dormancy in woody plants and gibberellin with dormancy
inhibition (Roberts and Hooley, 1988) is consistent with a hypothetical role of these
growth regulators in cold hardiness. Indeed, even though dormancy is not required
for hardening (Irving and Lanphear, l967a,b), still a rapid onset of rest and a
prolonged rest period are considered important for winter survival (Brierley and
Landon, 1946; Edgerton, 1954; Proebsting, 1963; Irving and Lanphear, 1967c; Howell
and Dennis, 1981). It is worth to recall that in Experiment Ileaf removal comprised
not only the removal of main leaves but also of lateral shoots at the treated nodes
of R vines. Howell and Shaulis (1980) found that the lack of persistent lateral canes
favored the hardiness of cane and primary bud tissues in cvs. Vignoles and Riesling.
Even though in that study, as in the present one, well exposed canes were sampled,
the presence of large lateral shoots conceivably resulted in poor light exposure of the
node from which the lateral shoot arose (Howell and Shaulis, 1980). Thus, the bud
at the insertion of a large lateral shoot (namely on a vigorous, non-fruiting vine),
would be relatively shaded compared to another bud at an equivalent node position
on a R vine, whose lateral shoot was removed. The import of assimilates might be
reduced due to shading in the former bud (May, 1965). However, it could also be the
case that growth inhibitor levels were higher in the latter, better exposed bud. Light
induces the formation of the growth inhibitor xanthoxin and can probably stimulate

ABA synthesis, given the evidence that xanthoxin is an ABA precursor (Burden gt

 

108
a1. , 1971). Moreover, the removal of lateral shoots probably corresponded to the

elimination of a source of gibberellins or of any hardiness inhibitor. This would favor

cold hardiness in situations where such removal did not drive the carbohydrate

content to a level below a critical point.

 

Leaf removal in 1989 and 1990 had no signiﬁcant effect on the number of
canes per vine with ﬁve or more mature nodes prior to pruning in the following
April, nor on the number and percentage of these canes that had the most favorable
(medium) diameter in April/1991, after two treatment seasons (Table 4). This may
suggest that leaf removal effects on cane maturity were of reduced practical meaning.
However, the number and percentage of canes with less than ﬁve mature nodes in
April/1991 was lower on R than on C vines, indicating that leaf removal enhanced
periderm development at the basal shoot region, conceivably due to improved light
conditions. This improvement would beneﬁt the canes, regardless of their number of
mature nodes. Neither in 1990 nor in 1991 was the percentage of shootless nodes
signiﬁcantly inﬂuenced by leaf removal in the preceding season (Table 5).

The number of canes per vine with ﬁve or more mature nodes was higher on
non-fruiting (0) than on fruiting (1.5 and NT) vines, both in 1990 and 1991. As
evaluated in April/1991, this effect was associated with a higher total number of
canes on the former vines, while the frequency distribution per cane diameter and
maturity classes was not signiﬁcantly inﬂuenced by cropping level. In a previous study

with Seyval, thinning improved cane maturity (Reynolds et al. , 1986); however, the

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109

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110

Table 5. Huber of nodes retained on mature field grown Seyval grapevines prior to treatment inposition
(1989), and influence of leaf removal and cropping level in the 1989 and 1990 seasons on the nulber of
nodes retained at prming and on the percentage of shootless nodes in the seasons following treatment

application (Experiment I).

 

Number of nodes retained

Percmtagiof shootless nodes

 

 

 

Treatment'
1989' 1990 1991 July 5/90 Jme 20/91
Leaf removal:
c 32 33 39 32.1 17.5
R 31 31 37 29.6 17.0
ns’I ns ns ns ns
Crop. level:
0 32 58a 62a 15.9b 10.6b
1.5 32 22b 28b 3b.8ab 19.9a
III 31 15c 26b 61.8a 21.2a
m m m it *
Interaction ns ns ns ns ns

 

'c:control (no leaves removed); Rzleaves removed on Septeaber 10189 and August 15/90;
0:0 clusters per vine; 1.5:1.5 clusters per node retained; Nszthinned

'At pruning prior to treatment inposition

‘ns, *, ** Non-significant or significant at the 5% or 1% level, respectively. Mean separation within

calm using the LSD test at 5%

111

vines were not balanced-pruned, which renders the results of that and of the present
study hardly comparable. The larger number of canes on non-fruiting vines in April
1991 (Table 4) reﬂects a larger number of nodes retained on these vines in 1990 (a
direct consequence of their larger size), and a lower percentage of nodes that failed
to develop subsequently (Table 5). In 1991 the percentage of shootless nodes was,
like in 1990, lower on non-fruiting than on fruiting (1.5 and NT) vines. The total
number of canes before pruning in 1991 was similar on 1.5 and NT vines (Table 4).
The NT vines had lower number and percentage of count-canes than the 1.5 vines,
though (data not shown), due to fewer nodes retained at pruning in 1990 and a
subsequently higher (but not signiﬁcant) percentage of shootless nodes (Table 5).
Although data were not analyzed across years, the percentage of shootless
nodes was clearly higher in 1990 than in 1991 (Table 5), in agreement with lower
cold hardiness in the 1989/90 than in the 1990/91 dormant seasons (Tables land 2).
Primary bud hardiness data were more consistent with the percentage of shootless
nodes than were cane hardiness data. In 1989/90, for instance, canes were hardier
on C than on R vines when all sampling dates were considered but the percentage
of shootless nodes in 1990 was similar in these vines. Moreover, in 1991 the lower
percentage of shootless nodes on non-fruiting (O) vines was not in correspondence
with the overall cane hardiness during the 1990/91 dormant season, which was lower
on 0 vines than on 1.5 vines. A relatively better agreement between bud hardiness
and percentage of shootless nodes was to be expected not only because the shoots
arise directly from the buds, but also because on mature vines (Tables 1 and 2), as

well as on the potted ones (Table 3) and in previous studies (Pogosyan and

 

112
Sarkisova, 1967; Byme and Howell, 1978; Howell and Shaulis, 1980), bud tissues

were generally more cold sensitive than cane tissues. Differences in primary bud
hardiness between C and R vines across 1989/90 and 1990/91 were not signiﬁcant,
the same being true for differences in the percentage of shootless nodes in 1990 and
1991. When all sampling dates in 1989/90 were considered, primary buds from O
vines were 2°C hardier than those from NT vines (Table 1). This was consistent with
an enhanced ﬁeld survival of the buds on 0 vines (approximately 16% of shootless
nodes in July/90 vs. 42% on NT vines) (Table 5). The inﬂuence of cropping level on
primary bud hardiness and on the percentage of shootless nodes continued, although
to a lesser degree, into the second year of the study. On average across the 1990/91
dormant season, there was a 1°C difference in primary bud hardiness between fnriting
and non-fruiting vines (Table 2); this difference was not statistically signiﬁcant but
appeared to be of Viticultural importance, as inferred from a lower percentage of
shootless nodes on non-fruiting relatively to fruiting vines in 1991 (about 11% on O
vines compared to 20% and 21% on 1.5 and NT vines, respectively) (Table 5).
Differences in percentage of shootless nodes, as in cane maturity and cold hardiness

between 1.5 and NT vines were not signiﬁcant in any of the trial years.

Conclusions

Cane and primary bud hardiness of young potted vines were not signiﬁcantly

affected by leaf removal, neither was primary bud hardiness on mature ﬁeld vines.

Leaf removal reduced cane hardiness on mature vines in 1989/90, but this was of no

 

113

consequence to ﬁeld survival during that dormant season. Indeed, the percentage of
shootless nodes in the ﬁeld was more consistent with primary bud than with cane
hardiness data, and was not signiﬁcantly affected by leaf removal in any trial years.

Mature ﬁeld vines unthinned in 1989 and 1990 (NT vines) had lower primary
bud hardiness through the 1989/90 dormant season, and lower ﬁeld bud survival in
1989/90 and 1990/91 than non-fruiting (O) vines. Differences in tissue hardiness, cane
maturity and percentage of shootless nodes between NT vines and vines thinned to
1.5 clusters per node retained (1.5 vines) were not statistically signiﬁcant in any of
the trial years. In 1990/91, canes were hardier on 1.5 than on O mature vines; in that
dormant season, fmiting potted vines had hardier cane and primary bud tissues than
non-fruiting ones.

Carbohydrate shortage conceivably limited cold hardiness on mature vines in
1989/90. An impaired carbohydrate accumulation in the fall of 1989 due to an early
leaf killing frost apparently aggravated the stress created by a heavy crop and by leaf
removal in 1989. This may in part explain the more pronounced treatment effects in
1989/90 than in 1990/91, and the relatively high T50 values and low ﬁeld bud survival
during the former dormant season. However, in some situations during the course of
this study, other factors were probably more relevant to hardiness than carbohydrate
levels. The removal of basal leaves and large lateral shoots in invigorated grapevines,
besides improving radiation microclimate at the basal shoot region, might have
decreased the supply to the buds of gibberellins or other likely hardiness inhibitor,
and/or increased the levels of abscisic acid, a supposed hardiness promotor. This

could have minimized, or even overridden a potential negative influence of leaf

1 l4
removal on cold hardiness, specially under non-limitin g carbohydrate conditions. This

hypothesis needs further investigation.

Some relationships were noticed in this study that were not statistically
signiﬁcant but deﬁned consistent patterns. Among them, there was, on mature vines,
a tendency for leaf removal to decrease primary bud hardiness in the mid-winter and
to increase it in the early spring, probably by delaying spring bud activity (F uchigami
et al., 1977; Mansﬁeld and Howell, 1981). This may explain the lack of a signiﬁcant
leaf removal effect on the percentage of shootless nodes following the dormant
seasons under study. Mid-winter hardiness data for potted vines suggested that
hardiness may be less affected by leaf removal at berry pea size than by removal at
veraison, which could indicate that an eventual compensation for leaf removal is
probably more effective following the earlier treatment date. This could not be
proven here, however, but should be given further, detailed evaluation in future

experimentation, because Viticultural implications are very important.

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Brierley, WJ. ,and R.H. Landon. 1946. Some relationships between rest period, rate
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Buttrose, M.S. 1968. Some effects of light intensity and temperature on dry weight
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Byme, M.F., and G.S. Howell. 1978. Initial response of Baco Noir grapevines to
pruning severity, sucker removal and weed control. Am. J. Enol. Vitic. 29:192-198.

Candolﬁ-Vasconcelos, M.C.1990. Compensation and stress recovering related to leaf
removal in Ems yinifera. PhD Diss., Swiss Federal Institute of Technology, Zurich.

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vineyards. Cornell Ext. Bull. 1127, N. York State College of Agriculture.

Edgerton, LJ. 1954. Fluctuations in the cold hardiness of peach ﬂower buds during
rest period and dormancy. Proc. Amer. Soc. Hort. Sci. 64:175-180.

Fuchigami, L.H. , M. Hotze, and C.J. Weiser. 1977. The relationship of vegetative
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Guy, C.L. 1990. Cold acclimation and freezing stress tolerance: role of protein
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Howell, G.S. 1988. Cultural manipulation of vine cold hardiness. In: Smart, R.E.,R.J.
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Climate Vitic. Enol., Auckland, New Zealand, Jan. 1988, pp. 98-102.

Howell, G.S., and F.G. Dennis. 1981. Cultural management of perennial plants to
maximize resistance to cold stress. In: Olien, C.R.,and M.N. Smith (Eds.). Analysis
and Improvement of Plant Cold Hardiness. CRC Press Inc. , Florida, 175-205.

Howell, G.S. , and N. Shaulis. 1980. Factors inﬂuencing within-vine variation in the
cold resistance of cane and primary bud tissues. Am. J. Enol. Vitic., 31:158-161.

Howell, G.S., and 8.8. Stackhouse. 1973. The effect of defoliation time on
acclimation and dehardening in tart cherry. J. Amer. Soc. Hort. Sci. 98:132-136.

Howell, G.S.,Stergios, B.G.,and S.S.Stackhouse. 1978. Interrelation of productivity
and cold hardiness of Concord grapevines. Am. J. Enol. Vitic. 29:187-191.

Howell, G.S.,and C.J. Weiser. 1970. Fluctuation in the cold resistance of apple twigs
during spring dehardening. J. Am. Soc. Hort. Sci. 95:190-192.

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Hunter, LL, and J .H. Visser. 1990. The effect of partial defoliation on growth
characteristics of m miter; L. cv. Cabernet Sauvignon. I. Vegetative growth. S.
Afr. J. Enol. Vitic. 11:18-25.

Irving, R.M.,and F.G. Lanphear. 1967a. Environmental control of cold hardiness in
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Irving, R.M., and F.G. Lanphear. 1967b. The long day leaf as a source of cold
hardiness inhibitors. Plant Physiol. 42:1384-1388.

Irving, R.M.,and F.O. Lanphear. 1967c. Dehardening and the dormant condition in
Ace: and Xibnmnm. Proc. Amer. Soc. Hort. Sci. 91:699-705.

Layne, R.E.C., and G.M. Ward. 1978. Rootstock and seasonal inﬂuences on
carbohydrate levels and cold hardiness of ‘Redhaven’ peach. J. Am. Soc. Hort. Sci.
103:408-413.

Levitt, J. 1956. The Hardiness of Plants. Academic Press Inc., New York. 278 pp.

Levitt, J. 1980. Responses of Plants to Environmental Stresses. Vol. 1. Chilling,
freezing, and high temperature stresses. Academic Press, New York. 497 pp.

Mansﬁeld, T.K., and G.S. Howell. 1981. Response of soluble solids accumulation,
fruitfulness, cold resistance, and onset of bud growth to differential defoliation stress
at veraison in Concord grapevines. Amer. J. Enol. Vitic. 32:200-205.

McKenzie, 1.8., and C.J. Weiser. 1975. Technique to inoculate woody plant stem
sections with ice during artiﬁcial freezing. Can. J. Plant Sci. 55:651-653.

May, P. 1965. Reducing inﬂorescence formation by shading individual Sultana buds.
Aust. J. Biol. Sci. 18:463-473.

Miller, D.P.,G.S. Howell, and R.K. Striegler. 1988. Cane and bud hardiness of own-
rooted White Riesling and scions of White Riesling and Chardonnay grafted to
selected rootstocks. Am. J. Enol. Vitic. 39:60—66.

Miillner, L., and G. Mayer. 1978. Die Frostharte der Rebe in Abhingigkeit vom
Witterungsverlauf wahrend der Winterruhe. Mitt. Klosterneuburg 28:175-184(Abstr.).

Pogosyan, KS, and M.M. Sarkisova. 1967. Frost resistance of grape varieties in
relation to the condition of hardening. Sov. Plant Phys. 14:886-891.

Proebsting, EL. 1963. The role of air temperatures and bud development in
determining hardiness of dormant Elberta peach fruit buds. Proc. Amer. Soc. Hort.
Sci. 83:259-269.

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Raese, J.T.,M.N. Williams, and H.D. Billingsley. 1978. Cold hardiness, sorbitol, and
sugar levels of apple shoots as inﬂuenced by controlled temperature and season. J.
Amer. Soc. Hort. Sci. 103:796-801.

Reynolds, A.G.,R.M. Pool, and LR. Mattick. 1986. Effect of shoot density and crop
control on growth, yield, fruit composition, and wine quality of ‘Seyval blanc’ grapes.
J. Amer. Soc. Hort. Sci. 111:55-63.

Roberts, J.A.,and R. Hooley. 1988. Plant Growth Regulators. Chapman & Hall, N.
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SAS Institute, Inc. 1985. SAS User’s Guide: Statistics. SAS Institute Inc., Cary, NC.
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Sakai, A. 1960. Relation of sugar content to frost hardiness in plants. Nature
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Shaulis, N.,J. Einset, and AB. Pack. 1968. Growing cold-tender grape varieties in
New York. NY. State Ag. Expt. Stn. Bull. No. 821, 16 pp.

Siminovitch, D.,C.M.Wilson, and D.R. Briggs. 1953. Studies on the chemistry of the
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Plant Physiol. 28:383—400.

Smart, R.E., N.J. Shaulis, and B.R. Lemon. 1982. The effect of Concord vineyard
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acclimation of Hglem helix. L. cv. Thomdalc. Physiol. Plant. 21:779-791.

Steponkus, P.L.,and S.C. Wiest. 1978. Plasma membrane alterations following cold
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Cold Hardiness and Freezing Stress. Academic Press, New York, pp. 75-91.

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28:34-42.

118

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Cool Climate Vitic. Enol., Auckland, New Zealand, Jan. 1988, pp. 95-97.

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Variation in cold hardiness within the canopy. Am. J. Enol. Vitic. 36:185-188.

Wolpert, J .A.,and G.S. Howell. 1986. Effect of night interruption on cold acclimation
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CHAPTERIII

Influence of Basal Leaf Removal and Cropping Level on the Growth, Canopy

Microclimate, Yield and Fruit Composition of Seyval Grapevines

119

120
Abstract

Basal leaf removal (R) had no signiﬁcant effect on vine growth, yield, and
fruit composition in either 1989 or 1990. Canopy microclimate was improved by leaf
removal; the photosynthetic photon ﬂux at the cluster region prior to harvest for R
vines was about twice that of control (C) vines. Leaf removal in 1989 had no
signiﬁeant effect on bunch rot levels. In 1990, when canopies were denser, a
signiﬁcant leaf removal x cropping level interaction was observed; leaf removal
decreased the rot incidence on vines thinned to 1.5 clusters per node retained (1.5
vines) but had no signiﬁcant effect on unthinned (NT) vines.

Thinning to 1.5 clusters per node retained had no signiﬁcant effect on vine
yield. In 1989 the lower number of clusters on 1.5 relative to NT vines was
compensated for by heavier clusters; in 1990 there were no signiﬁcant differences in
yield components between 1.5 and NT vines. Two consecutive non-thinned years
followed by one year of thinning to 1.5 clusters per node retained had no signiﬁcant
effect on ﬁnal vegetative growth, relative to annual thinning to 1.5 clusters per node
retained. In 1991, when all vines were thinned to 1.5 clusters per node retained, yield
was highest on the vines that did not bear fruit in the preceding two seasons (0
Vines). This was due to these vines having larger size in 1991, hence larger number
Of nodes and clusters retained; no signiﬁcant differences in other yield components

Were found. Unlike in previous years, the ﬁnal shoot length in 1991 and the vine size
in 1992 did not signiﬁcantly differ among vines that were defruited and those that

bOIe fruit in 1989 and 1990.

121
In 1989 fruit titratable acidity was higher on 1.5 than on NT vines while no

signiﬁcant differences in °Brix and pH were observed. Thinning had no signiﬁeant
effect on fruit composition in 1990. In 1991 "Brix was highest on the vines that had
been unthinned in 1989 and 1990 and lowest on the vines that bore no clusters in
those years. In the ﬁrst trial year, bunch rot incidence was lower on NT than on 1.5
vines, probably due to lower cluster compactness on the former vines. No signiﬁcant

differences in rot scores among cropping levels were observed thereafter.

Introduction

Seyval (Seyve-Villard 5-276) is an important white wine cultivar in Eastern
United States viticulture (Reynolds e1 31.,1985;Kaps and Cahoon, 1989). It produces
large, compact clusters, is susceptible to bunch rot, and has a propensity to overcrop.
In Seyval grapevines, as in many French-American hybrids, pruning alone does not
seem to provide adequate crop control, and adjustment by thinning has been used
(Fisher et 31., 1977; Pool gt 31.,1978; Reynolds 91 31., 1986;1(aps and Cahoon, 1989).
Thinning to 1.5 clusters per node retained at pruning is a recommended practice to
complement balanced-pruning of Seyval vines. Basal leaf removal, by improving the
microclimate in the cluster zone, may reduce the incidence of bunch rot as observed
On other cultivars (Wolf et 31., 1986; Gubler, 1987; Koblet, 1987,1988; Kliewer and
Bledsoe, 1987; Bledsoe et 31., 1988; Smith et 31., 1988; English :1 31., 1989).
The economical advantage of leaf removal has been proven on some high

Value cultivars (Smith et 31., 1988). The value of this cultural practice can not be

122
generalized, though, given conﬂicting reports of leaf removal effects on vine growth,

yield and fruit composition. Defoliation reduced berry weight (Weaver, 1963;
Buttrose, 1966; May :1 31., 1969; Kliewer and Antcliff, 1970; Kingston and van
Epenhuijsen, 1989), clusters per node, and/or berries per cluster (May gt 4, 1969;
Mansﬁeld and Howell, 1981). This contrasts with reports where yield was not affected
(Kliewer and Bledsoe, 1987; Bledsoe et 31., 1988). Buttrose (1966) and Kliewer and
Antcliff (1970) reported a reduction in % soluble solids, while Kliewer et 31. ( 1988)
showed fruit composition to be either unaffected or enhanced by leaf removal. This
diversity can be attributed to differences in variety, site climate, fruit exposure to
sunlight, nature of the leaves removed (age, position, light environment), timing and
severity of removal, and vine size, among other factors (Kliewer and Bledsoe, 1987;
Reynolds and Wardle, 1989; Zoecklein, 1989).

In temperate zone grape regions a relevant aspect in the adoption of any new
cultural practice is its potential inﬂuence on cold hardiness. In a previous chapter of
this work it was shown that the removal of basal leaves had no signiﬁcant effect on
primary bud hardiness in the dormant season following removal, nor on the
percentage of nodes that developed in the next growing season. This study aimed at
estimating the impact of this practice on the vegetative growth, light microclimate,
yield, fruit composition, and bunch rot incidence on mature, differentially cropped

ﬁeld-grown Seyval grapevines.

123
Materials and Methods

 

Own-rooted, mature, bearing Seyval grapevines planted in 1983 at the
Clarksville Horticultural Experimental Station (CHES) , Clarksville, Michigan, were
used in this experiment. Vine spacing was 2.4m x 3.0m within and between the rows
and the vines were trained to Hudson River Umbrella (a bilateral cordon at the top
wire) with the top wire at 1.8 m height and a N-S row orientation. The vines were
balanced-pruned using a 15+10 pruning formula (Reynolds :1 31., 1986) up to a
maximum of 65 nodes retained per vine. A more detailed description of the vineyard
installation and maintenance was presented in Chapter 1.

Prior to the 1989 growing season a randomized block design was established.
Vine size (assessed by the weight of one-year old cane prunings), which varied
between 1.0kg and 1.5 kg), was used as the blocking variable. Five blocks of six vines
were deﬁned, one vine per treatment combination.

Leaf removal and cropping level treatments were arranged in a 2x3 factorial.
The leaf removal levels were: C = no leaves nor lateral shoots removed (control);
R = main leaves and lateral shoots removed at three basal nodes on all the shoots
of the vine. The cropping levels were: 0 = 0 clusters per vine; 1.5 = 1.5 clusters per
node retained at pruning; NT = all clusters retained (no thinning). In 1990 each vine
was treated as in 1989. In 1991, all vines were thinned to 1.5 clusters per node
retained and no leaf removal was applied. Cluster thinning was done on June 12/ 89

(one week before full bloom), June 27/90 (9 days after full bloom), and June 15/91

124
(12 days after full bloom). Leaf removal was imposed on September 10/89 (2.5 weeks

after veraison) and August 15/90 (veraison). On fruiting shoots, leaves and lateral
shoots opposite, one node above, and one node below the basal cluster were
removed. 0n non-fruiting shoots, leaves and laterals were removed from equivalent
node positions. Lateral shoots were allowed to develop normally except for those at
the three treated nodes on the defoliated vines.

0f the total number of buds retained at pruning in 1990 and thereafter
(ealculated by the 15+ 10 pruning formula), two-thirds were left on 6-node canes and
the remaining on 2-node spurs. By doing so, not only the ratio of buds on caneszbuds
on spurs was maintained but also, in the case of the vines that had been previously
subjected to leaf removal, the proportion of the buds that were retained at defoliated
node positions was standardized. Indeed, given the position of the defoliated nodes,
this procedure resulted in retaining 50% of the count-buds (buds counted in
balanced-pruning) at positions defoliated in the previous season and 50% at non-

defoliated positions.

[I . I'm

Instantaneous photosynthetic photon ﬂux (PPF) was measured at 1.5 weeks
before harvest in 1989 and on ﬁve occasions during the 1990 growing season, using
Li-Cor LI-1000 quantum sensors connected to a data logger. Three sensors were
attached to a wooden bar. The bar was horizontally inserted perpendicular to the
row, across the fruiting zone of each vine (about 0.15 m below the cordon), at seven

(in 1989) or ﬁve (in 1990) locations in the eanopy. The two lateral sensors were at

125

0.20 m from the cordon; the middle one was offset towards the west side of the
eanopy, not to be positioned directly below the cordon. Measurements were taken
on sunny days between 11:00H and 14:00H. PPF data were expressed as the
percentage relative to the ambient horizontal above the canopy, determined just
before the measurements for each vine. Analysis was done for the mean percentage
PPF per vine, calculated as the average over all the observations on the vine.
Canopy structure was evaluated using the point quadrat technique (Wilson,
1960; Smart, 1982; Smart and Smith, 1988). A thin, I m needle, was inserted at a 45°
angle across the fruiting zone. Assessments were made on the day before harvest in
1989 and through the 1990 vegetative season. At each measurement date, ten random
insertions per vine were done, giving a total of ﬁfty insertions per treatment
combination. The sequence of contacts with leaves and clusters as well as the number
of gaps was recorded. Leaf layer number (LLN) , percent gaps, percent interior leaves

and percent interior clusters were calculated as proposed by Smart and Smith (1988).

1!. . ll . H l E . i'
Harvest was done on September 27/ 89, September 25/90 and September

6/ 91 . Immediately prior to harvest, ﬁve random clusters per vine were evaluated for
the incidence of bunch rot, m cinema Pers. The following 5-point scale was
used, based on the approximate percentage of rotten berries per cluster: 1- ~100%;
2- ~75%; 3- ~50%; 4- ~25%; 5- ~0%. In addition, each vine wasscored according
to the percentage of rotten clusters (i.e. ,clusters in classes four or lower), using a 5-

point seale as follows: 1- 80-100%; 2- 60-80%; 3- 40—60%; 4- 20-40%; 5- 0-20%.

126
Also just before harvest, a sample of berries was obtained from each replicate

(vine) for berry weight assessment and fruit analysis. In 1989 and 1990, two apical
berries from twenty-ﬁve randomly selected clusters per vine (excluding clusters on
lateral shoots) were sampled. Vines were harvested individually. The clusters on
lateral shoots (second crop) were not picked. Mean cluster weight was calculated by
dividing yield by cluster number. Berries per cluster was calculated by dividing cluster
weight by berry weight. In 1991, ﬁve apical berries were taken from each of two
clusters on ﬁve previously tagged shoots per vine. These shoots had been selected
two weeks after full bloom for being representative of the vine’s shoots and for their
node of origin. Only shoots at node positions two and three from the base of the
spurs and eanes were tagged (defoliated in 1990 in the case of R vines). Clusters
from the selected shoots were harvested and weighed separately from the other
clusters of the vine. Total number of clusters and yield per vine were measured and
used to calculate the overall mean cluster weight per vine; in addition, the mean
cluster weight, berry weight and number of berries per shoot were calculated based
on the harvest data for the tagged shoots.

The berries taken from each vine were crushed, the juice was strained through
cheesecloth, and analyzed for total % soluble solids (°Brix), titratable acidity and pH

using standard analytical methods described by Ough and Amerine (1988). n

51 ! 1 vi .
On October 23/1989, October 24/1990 and October 18/1991 (approximately

one month after harvest), ﬁve random canes per vine (twenty-ﬁve canes per

127

treatment combination) were randomly selected. Cane length, number of nodes per
cane and intemodc length were determined, and the mean values per vine were
calculated.

Vine size was assessed every year at pruning as the weight of l-year-old cane
prunings. In 1990 and 1991 vine size was obtained by adding the weight of the cane
prunings from each vine to the weight of the canes removed from that vine for cold

hardiness assessments in the previous dormant season.

5 . . l l .

Data (except point quadrat determinations) were subjected to analysis of
variance using the GLM procedure of the Statistical Analysis System (SAS Institute
Inc. , 1985). Leaf removal and cropping treatments were analyzed as a two-factor
factorial set in a randomized block design.

Percentage of PPF values were subjected to the arc-sine of the square root
transformation prior to analysis. When more than one PPF measurement date was
analyzed, date was considered a blocking variable. In the analyses of harvest data for
1989 and 1990 the two levels of leaf removal (C and R) were combined with two
cropping levels (1.5 and NT). Because all vines were treated alike in 1991, the
harvest data that year reﬂects the carryover effect of the treatments applied in 1989
and 1990; therefore three cropping levels (0, 1.5, and NT) and two leaf removal
levels (C and R) were considered.

When the F-values were signiﬁcant at 5 % or lower level, mean separation was

done using the LSD test at the 5% level.

128
Results and Discussion

Leaf removal had no signiﬁcant effect on vine growth, yield components and
fruit composition during the trial years (Tables 1, 2, 3 and 4); similar results were
found in the treatment season in two leaf removal experiments with potted Seyval
vines (results not shown). The low intensity and the timing of leaf removal might
have contributed to the lack of signiﬁcant effects. Nevertheless, in a study with
Sauvignon blanc grapevines in which four leaf removal levels (control plus low to
moderate removal intensities) and three treatment dates (fruit set, four and seven
weeks after fruit set) were investigated, no treatment effects on yield and yield
components were likewise observed (Kliewer et 31., 1988; Bledsoe 91 31, 1988).
Similarly, berry number and berry weight were not signiﬁcantly affected by leaf
removal applied to Sauvignon blanc and Cabernet Sauvignon as early as ﬂowering
and early fruit set (Smith et 31., 1988). Signiﬁcant reductions in berry weight in the
season of leaf removal have been reported (Weaver, 1963; Buttrose, 1966; May 91
31.,1969;Kliewer, 1970; Kliewer and Antcliff, 1970; Kingston and Van Epenhuijsen,
1989; Candolﬁ-Vasconcelos and Koblet, 1990) but they occurred under severe
defoliation and/or hot climate conditions. When both conditions are present, the
berries are conceivably exposed to high radiation levels for prolonged periods and
a concomitant rise in temperature may, by itself, cause a reduction in berry weight
(Bledsoe gt 3.1.,1988).

No signiﬁcant differences in yield were found between the vines thinned to 1.5

clusters per node retained (1.5 vines) and the unthinned (NT) ones, in either 1989

129
or 1990 (Tables 1 and 2). Because vine size was the blocldng variable in the

establishment of this experiment in 1989, vine size and number of nodes retained at
pruning in 1989 were similar among the vines subjected to the different treatments.

In that year, reduced cluster number on 1.5 relative to NT vines was compensated

for by heavier clusters, resulting from an additive effect on the number of berries per
cluster and berry weight, although neither component was signiﬁcantly inﬂuenced per
5; (Table l). The vegetative development of the NT vines in 1989 was more affected
by cropping than that of 1.5 vines, as evidenced by a smaller size of the former vines
at pruning in 1990 (Table 2). This suggests that a similar yield is more demanding

of the vine when distributed over a larger number of clusters. In 1990, balanced-

pruning resulted in fewer nodes retained on NT than on 1.5 vines; at harvest there
were no signiﬁcant differences in cluster number or other yield components between
the two (Table 2). In previous studies, an increase in berry weight in the year of
thinning minimized or compensated for the reduction in vine cluster number
(Looney, 1981; Bravdo et 31., 1984; Reynolds :1 31.,1986;Kaps and Cahoon, 1989).
In ‘Carignane’ grapevines, thinning immediately after full bloom reduced yield only
when at least two-thirds of the clusters were removed (Bravdo et 31. , 1984). Thinning
was applied at an earlier stage in 1989 (one week before full bloom) than in 1990
(nine days after full bloom). The lack of a signiﬁcant thinning effect on the number
of berries per cluster in either year reﬂects a reduced cluster thinning inﬂuence on
berry set, in agreement with previous works (Hale and Weaver, 1962; Looney, 1981).
Hale and Weaver (1962) observed that clusters were relatively weak sinks during the

pre-bloom and setting period. They concluded that during these stages the practices

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131

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132
that can be expected to inﬂuence set are those like topping or girdling, which modify

or eliminate either of the two major sinks for assimilates at that time, i.e. , the shoot
tips or the parent vine.

In 1991, when all vines were treated similarly, vine cluster number and yield
did not signiﬁcantly differ between the vines that bore fruit in 1989 and 1990,
regardless of thinning treatment (NT vs. 1.5) in those years. Non-bearing vines in
1989 and 1990 had the largest size in 1990 and 1991. Consequently, they were
ascribed the highest number of nodes and clusters in 1991, and achieved the highest
yield. However, no signiﬁcant differences in cluster weight, berries per cluster and
berry weight were found among cropping levels in 1991 (Table 3). This could in part
reﬂect a greater homogeneity of the clusters as a consequence of the shoot selection
criteria used in 1991; however, differences were also non-signiﬁcant when the mean
cluster weight was calculated considering all clusters on the vine. At the end of 1991,
there were no signiﬁcant differences in shoot length among differently cropped vines
in 1989 and 1990 (Table 4); similarly, no signiﬁcant differences in vine size were
found at pruning in 1992 (Table 3).

Data were not analyzed across years, but a reduction in yield from 1989 to
1990 is clear (Tables 1 and 2). The lower yield in 1990 allowed for more vegetative
growth, as evidenced by longer canes on fruiting vines at the end of the 1990
compared to the 1989 season (Table 4) and, specially, by the increase in vine size of
1.5 and NT vines from 1990 to 1991 (Tables 2 and 3). The main reasons that might
have contributed to the low 1990 yield are: a) inﬂorescence primordia formation

inhibited on the fruiting (1.5 and NT) vines in the 1989 season due to a relatively

133

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135
high crop (Chapter IV); b) inhibited growth of the fruiting vines in 1989; hence the

number of nodes retained at pruning and the number of clusters per vine were lower
in 1990than in 1989; c) high bud mortality in the 1989/90 dormant season, expressed
by a high percentage of shootless nodes in 1990 on the fruiting vines (Chapter II)
and, therefore, a low percentage of clusters on shoots originated from count-nodes.
Indwd, prior to thinning in 1990, clusters from count-nodes represented only 45%
and 25% of the total number of clusters on 1.5 and NT vines, respectively (data not
shown). This percentage was higher in 1991 (63% and 64% on 1.5 and NT vines
respectively) following the milder 1990/91 dormant season, and probably also in 1989
(not evaluated) due to low bud mortality during the 1988/ 89 dormant season at the
experimental Seyval plot (Howell, 1989). Clusters arising from count positions have
been shown to be heavier than clusters from non—count positions (Pool et a1. , 1978;
Wolpert gt a1.,1983).

Cropping level had no signiﬁcant effect on fruit % soluble solids and pH in
1989 and 1990 (Tables 1 and 2), unlike in reports where thinned vines had higher
°Brix (Fisher et a1.,1977;Looney, 1981; Howell e1 11.,1987;Kaps and Cahoon, 1989).

In a previous Seyval study, only two of four years showed a decrease in °Brix with

decreasing thinning levels from 10 to 25 clusters/500g of cane prunings (Reynolds gt .

31., 1986). In 1989, titratable acidity was lower on NT than on 1.5 vines for a
comparable °Brix (Table 1); based on Bravdo :1 ﬂ. (1984), this suggests that the NT
vines were overcropped. In 1991 there were clear differences in fruit composition
among 0, 1.5, and NT vines (abbreviations relative to cropping treatments in 1989

and 1990) (Table 3). The highest °Brix was found on the NT vines followed, in order,

 

136
by the 1.5 and the 0 vines; the NT vines also had the highest pH. The lower

composition value of the O vines was probably due to the high yield of these vines,
leaf and cluster shading resulting from shoot crowding, or both.

The point quadrat and PPF assessments prior to harvest in the treatment
seasons (mid to late September) clearly reﬂect the higher vegetative growth in 1990
compared to 1989 (Tables 5, 6, 7 and 8). Leaf removal improved the light
microclimate and the canopy characteristics in both seasons and conceivably
increased air movement in the cluster region. At the preharvest measurement, the
mean percentage of PPF reaching the cluster region was about twice as high on
defoliated than on control vines both in 1989 and 1990 (Tables 6 and 8). However,
no signiﬁeant leaf removal effect on cluster and vine rot scores was found in 1989.
In that year, rot incidence was lower on NT than on 1.5 vines, probably due to lower
cluster compactness on the former vines (Table 1; Smithyman, 1992). In 1990 the
vine rot score was inﬂuenced by a signiﬁcant leaf removal x cropping level
interaction (Table 2); an inspection of the treatment combination means revealed
that leaf removal reduced the percentage of rotten clusters on 1.5 vines but had no

signiﬁcant effect on NT vines (data not shown).

Conclusions

The removal of three basal leaves and adjacent laterals on all vine shoots had

little impact on vine growth, yield, yield components and fruit composition in the

treatment seasons (1989 and 1990). Light microclimate and canopy parameters were

137

Table 5. Influence of leaf removal and cropping level on canopy parameters of
mature Seyval grapevines on September 26/89, the day before harvest in the
first treatment season, as evaluated by point quadrat analysis.‘

 

 

Treatment' Leaf layer X Gaps X Interior X Interior
number (LLN) leaves. clusters
Leaf removal: C 1.81 6.6 23.9 32.0
R 1.27 10.6 13.5 7.0
Crop. level: 0 1.83 12.1 19.8 __
1.5 1.38 5.3 17.7 13.2
NT 1.60 5.9 20.5 26.6

 

'Based on 50 insertions per treatment combination (150 and 100 insertions per
leaf removal level and per cropping level, respectively)

'C:control (no leaves removed); R:leaves removed on September 10/89
0:0 clusters per vine; 1.5:1.5 clusters per node retained; NT:unthinned.
Thinning date: June 12/89.

Table 6. influence of leaf removal and cropping level on the percentage of
photosynthetic photon flux (PPF) reaching the cluster region of the canopy of
mature Seyval grapevines on September 17/89, 1.5 weeks before harvest in the
first treatment season.‘

 

 

Treatment' PPF (X of ambient)
Leaf removal: c 15.5b
R 33.1a
”t‘
Crop. level: 0 17.6b
1.5 29.3a
NT 26.3ab
e
lnteraction ns

 

'Based on 105 readings per treatment combination (315 readings per leaf removal
level and 210 readings per cropping level, respectively)

'C:control (no leaves removed); R:leeves removed on September 10/89

0:0 clusters per vine; 1.5:1.5 clusters per node retained; NT:unthinned.
Thinning date: June 12/89

‘ns, *, '*, *** Non significant or significant at the 5%, 1% or 0.1% level,
respectively. Mean separation within columns using the LSD test at 5%.

 

138

Table 7. Influence of leaf removal and cropping level on canopy parameters of matur'e Seyval grapevines
wring 1990, the second treatment season, as evaluated by point quadrat analysis.

 

 

Average
Treetment' Jme 28 July 9 July 18 July 25 Aug. 7 Aug. 16 Aug. 31 Sep. 17
1.5 all 3 wk 6 Hit 5 wk 1 uk V 2 wk 1 Hit Over the Since
PFB' PFB PFB PFB 8V PV' 8“ 1990 leaf

season removal
Leaf Layer umber (LLN)

 

Leaf removal

 

 

c 1.26 2.35 3.07 3.17 3.53 3.83 6.63 6.60 6.62

R 1.02 2.01 2.57 2.67 3.05 3.29 3.03 3.50 3.27
Crop. level

0 1.28 2.57 3.52 3.77 6.66 6.82 6.81 6.96 3.77 6.88

1.5 1.12 1.96 2.67 2.63 3.01 3.00 3.53 3.76 2.66 3.66

NT 1.02 2.02 2.67 2.27 2.60 2.85 3.16 3.67 2.66 3.31

i Gaps

Leaf removal

C 19.6 2.5 0 0 0 0

R 17.9 5.6 6.7 2.7 1.3 1.3 0.7 0 0.7
Crop. level

0 22.2 1.6 1.0 1.0 0 0 0 0 3.2

1.5 21.0 1.1 1.0 0 0 0 0 0 2.9

RT 25.7 9.3 5.0 3.0 2.0 2.0 1.0 0 6.0 0.5

 

i lnterior leaves

 

Leaf removal

C 8.6 28.0 61.6 62.9 50.1 51.9 58.6 57.2 57.8

R 10.9 21.0 33.8 35.9 63.2 66.8 61.9 68.0 65.0
Crop. level

0 9.3 30.0 62.9 67.2 55.2 58.5 58.6 59.5 65.1 59.0

1.5 10.6 18.5 36.0 36.2 66.2 61.0 69.3 51.3 35.6 50.3

NT 8.6 26.1 36.8 31.7 35.0 60.0 66.6 66.6 33.2 65.5

 

i Interior clusters

 

Leaf removal

c 30.6 56.5 56.9 55.6 56.3 61.7 81.0 91.2 86.1

R 11.1 65.9 69.0 38.2 62.3 58.7 50.0 56.5 53.3
Crop. level

0 _ _ _ _ _ _ _ __ _ _

1.5 18.6 67.6 56.7 62.9 56.7 62.7 65.5 67.2 51.7 66.6

RT 15.2 53.7 51.1 66.6 65.8 57.6 63.0 78.7 51.2 70.9

 

‘Based on 50 insertions per treatment coubination (150 and 100 insertions per leaf removal level and
per cropping level, respectively)

'c:control (no leaves removed); R:leaves removed on Septeaber 10/89 and August 15/90

0:0 clusters per vine; 1.5:1.5 clusters per node retained; “unthinned. Thinning dates: Jme 12/89
and Jtne 27/90

I‘Time in weeks (wk) relative to vine phenophases:

PFB:post full bloom; 8V:before veraison; V: veraison; Pv:post veraison; BH:before harvest
'First assessment after leaf removal in 1990.

139

Table 8. Influence of leaf removal and cropping level on the percentage of photosynthetic photon flux
(PPF) reaching the cluster region of the canopy of mature Seyval grapevines during 1990, the second
treatment season.’

 

 

Treatment' PPF (% of aLbient) AveraE
July 16 July 26 Aug.7 Aug. 31 Sep. 15 Over the Since
6 wk 5 wk 1 wk 2 wk 1.5 wk 1990 leaf
PFB' PFB BV PV" BH season removal

 

 

Leaf removal

0 27.0 18.9 16.9 11 .6b 10.8b 11 .213
R 28.3 26.3 19.2 21.7a 19.9a 20.8a
ns" ns“ ns ** * *"
Crop. level
0 22.6 12.2b 11.1b 10.5b 10.2 12.5c 10.6b
1.5 26.2 22.5ab 16.8ab 16.6ab 16.2 18.5b 16.6a
NT 37.5 33.0a 23.0a 22.9a 19.6 25.5a 21.2a
ns eee e ee ns m at.
lnteraction ns ns ns ns ns ns

 

'Based on 75 readings per treatment conbination (225 and 150 readings per leaf removal level and per
cropping level, respectively)

'C:control (no leaves removed); R:leaves removed on September 10/89 and August 15/90

0:0 clusters per vine; 1.5:1.5 clusters per node retained; RT:unthinned. Thinning dates: June 12/89
and June 27/90 .

I‘Time in weeks (wk) relative to vine phenophases

PFB:post full bloom; Bv:before veraison; V: veraison; PV:post veraison; 8H:before harvest
”First assessment taken after leaf removal in 1990.

'ns, *, **, *** Non significant or significant at the 5%, 1% or 0.1% level, respectively. Mean
separation within columns using the LSD test at 5%.

“Ps0.0562

 

140
improved by leaf removal in both seasons. In 1990 a light crop was associated with

an intense growth and high canopy density, which may have contributed to increased
m infection. Leaf removal had no signiﬁcant effect on cluster and vine rot
scores in 1989; in 1990, however, leaf removal reduced the percentage of rotten
clusters on vines thinned to 1.5 clusters per node retained (1.5 vines) but had no
signiﬁcant effect on unthinned (NT) vines. The above results are consistent with the
view that vines with denser canopies are more likely to beneﬁt from an improved
m control by leaf removal. There is, however, a need to further evaluate the
practice as well as the economics of leaf removal in Seyval, before recommendations
can be made.

During this study, yield and yield components were not signiﬁcantly different
on 1.5 and NT vines, except for a higher cluster weight on 1.5 vines in 1989, which
compensated for a lower cluster number. In that year, mm incidence was lower
on NT than on 1.5 vines, probably due to less compact clusters on the former. Two
consecutive non-thinned years followed by one year of thinning to 1.5 clusters per
node retained increased the °Brix in the third year, with no signiﬁcant reduction in
the ﬁnal vegetative growth (as compared to annual thinning to 1.5 clusters per node
retained). The initial vine size (which ranged from 1.0 to 1.5 kg) appeared to be
sufﬁcient to support two consecutive seasons without thinning. Moreover, the fact
that all vines were balanced-pruned undoubtedly contributed to minimize any
eventual vegetative/reproductive imbalance resulting from unthinning. The above
results and the increased labor costs associated with cluster thinning make systematic

thinning questionable and motivate a further investigation on the value of pluriannual

 

141
cluster thinning in Seyval.

literature cited

Bledsoe, A.M.,W.M. Kliewer, and J .J . Marois. 1988. Effects of timing and severity
of leaf removal on yield and fruit composition of Sauvignon Blanc grapevines. Am.
J. Enol. Vitic. 39149-54.

Bravdo, B.,Y. Hepner, C. Loinger, S. Cohen, and H. Tabacman. 1984. Effect of crop
level on growth, yield and wine quality of a high yielding Carignane vineyard. Am.
J. Enol. Vitic. 35:247-252.

Buttrose, M.S. 1966. The effect of reducing leaf area on the growth of roots, stems
and berries of Gordo grapevines. Vitis 5:455-464.

Candolﬁ-Vasconcelos, M.C., and W. Koblet. 1990. Yield, fruit quality, bud fertility
and starch reserves of the wood as a function of leaf removal in Vig’s vinifera -
Evidence of compensation and stress recovery. Vitis 29:199-221.

English, J.T., C.S. Thomas, J.J. Marois, and W.D. Gubler. 1989. Microclimates of
grapevine canopies associated with leaf removal and control of m bunch rot.
Phytopathology 79:395—401.

Fisher, K.H., G.A. Bradt, J. Wiebe, and V.A. Dirks. 1977. Cluster-thinning ‘de
Chaunac’ French hybrid grapes improves vine vigor and ﬁlm quality in Ontario. J.
Amer. Soc. Hort. Sci. 102:162-165.

Gubler, W.D. 1987. Control of m bunch rot of grape with canopy management.
Plant Dis. 71:599-601.

Hale, C.R. , and R.J. Weaver. 1962. The effect of developmental stage on direction
of translocation of photosynthate in Ems 21m. Hilgardia 33:89-131.

Howell, G.S. 1989. 1989 Freeze damage analyses: Did the winter cold or the spring
frost reduce the 1989 crop?. Vintner & Vineyard. Michigan State Univ. Coop. Ext.
Service Bull., vol. 3, no.3, pp. 6—8.

Howell, G.S.,T.K. Mansﬁeld, and J .A. Wolpert. 1987. Inﬂuence of training system,
pruning severity, and thinning on yield, vine size, and fruit quality of Vidal blanc
grapevines. Am. J. Enol. Vitic. 38:105-112.

 

 

142

Kaps, M.L.,and G.A. Cahoon. 1989. Berry thinning and cluster thinning inﬂuence on
vegetative growth, yield, fruit composition, and net photosynthesis of ‘Seyval blanc’
grapes. J. Amer. Soc. Hort. Sci. 114:20—24.

Kingston, C.M.,and C.W. van Epenhuijsen. 1989. Inﬂuence of leaf area on fruit
development and quality of Italia glasshouse table grapes. Am. J. Enol. Vitic. 40: 130-
134.

Kliewer, W.M. 1970. Effect of time and severity of defoliation on growth and
composition of ‘Thompson Seedless’ grapes. Am. J. Enol. Vitic. 21:37-47.

Kliewer, W.M.,and A.J. Antcliff. 1970. Inﬂuence of defoliation, leaf darkening, and
cluster shading on the growth and composition of Sultana grapes. Am. J. Enol. Vitic.
21:26-36.

Kliewer, W.M.,and A.M. Bledsoe. 1987. Inﬂuence of hedging and leaf removal on
canopy microclimate, grape composition, and wine quality under California
conditions. Acta Horticulturae 206:157-168.

Kliewer, W.M.,J.J. Marois, A.M. Bledsoe, S.P. Smith, M.J. Benz, and O. Silvestroni.
1988. Relative effectiveness of leaf removal, shoot positioning, and trellising for
improving winegrape composition. In: Smart, R.E., R.J. Thornton, S.B. Rodriguez,
and J .E. Young (Eds.). Proc. 2nd Intnl. Symp. Cool Climate Vitic. Enol., Auckland,
New Zealand, Jan. 1988, pp. 123-126.

Koblet, W. 1987 . Effectiveness of shoot topping and leaf removal as a means of
improving quality. Acta Horticulturae 206:141-156.

Koblet, W. 1988. Canopy management in Swiss vineyards. In: Smart, R.E., R.J.
Thornton, S.B. Rodriguez, and J.E. Young (Eds.). Proc. 2nd Intnl. Symp. Cool
Climate Vitic. Enol., Auckland, New Zealand, Jan. 1988, pp 161-164.

Looney, N.E. 1981. Some growth regulator and cluster thinning effects on berry set
and size, berry quality, and annual productivity of de Chaunac grapes. Vitis 20:22-35.

Mansﬁeld, T.K., and G.S. Howell. 1981. Response of soluble solids accumulation,
fruitfulness, cold resistance, and onset of bud growth to differential defoliation stress
at veraison in Concord grapevines. Amer. J. Enol. Vitic. 32:200-205.

May, P., NJ. Shaulis, and A.J. Antcliff. 1969. The effect of controlled defoliation in
the Sultana vine. Am. J. Enol. Vitic. 20:237-250.

Ough, C.S.,and M.A. Amerine. 1988. Methods for Analysis of Musts and Wines. J.
Wiley and Sons, N. York. 377pp.

143

Pool, R.M.,C. Pratt, and H.D. Hubbard. 1978. Structure of base buds in relation to
yield of grapes. Am. J. Enol. Vitic. 29:36—41.

Reynolds, A.G., R.M. Pool, and LR. Mattiek. 1985. Effect of training system on
growth, yield, fruit composition, and wine quality of Seyval blanc. Amer. J. Enol.
Vitic. 36:156-164.

Reynolds, A.G.,R.M. Pool, and LR. Mattiek. 1986. Effect of shoot density and crop
control on growth, yield, fruit composition, and wine quality of ‘Seyval blanc’ grapes.
J. Amer. Soc. Hort. Sci. 111:55-63.

Reynolds, A.G. , and D.A. Wardle. 1989. Impact of various canopy manipulation
techniques on growth, yield, fruit composition, and wine quality of Gewurztraminer.
Am. J. Enol. Vitic. 40:121-29.

SAS Institute, Inc. 1985. SAS User’s Guide: Statistics. SAS Institute Inc., Cary, NC.
956 pp.

Smart, R.E. 1982. Vine manipulation to improve wine grape quality. In: Webb, A.D.
(Ed.). Proc. Grape and Wine Centennial Symp. Univ. California, Davis, June 1980,
pp. 362-375.

Smart, R.E., and SM. Smith. 1988. Canopy management: identifying the problems
and practical solutions. In: Smart, R.E., R.J. Thornton, S.B. Rodriguez, and J.E.
Young (Eds.). Proc. 2nd Intnl. Symp. Cool Climate Vitic. Enol., Auckland, New
Zealand, Jan. 1988, pp. 109-115.

Smith, S.,I.C. Codrington, M. Robertson, and R.E. Smart. 1988. Viticultural and
ocnological implications of leaf removal for New Zealand vineyards. 1n: Smart, R.E. ,
R.J. Thornton, S.B. Rodriguez, and J.E. Young (Eds.). Proc. 2nd Intnl. Symp. Cool
Climate Vitic. Enol., Auckland, New Zealand, Jan. 1988, pp. 127-133.

Smithyman, R.P. 1992. Personal communication, unpublished data. Michigan State
University.

Weaver, R.J. 1963. Effect of leaf to fruit ratio on fruit quality and shoot development
in Carignane and Zinfandel wine grapes. Am. J. Enol. Vitic. 14:1-12.

Wilson, W. 1960. Inclined point quadrats. New Phytol. 59:1-8.
Wolf, T.K., R.M. Pool, and LR. Mattiek. 1986. Responses of young ‘Chardonnay’

grapevines to shoot tipping, cthcphon and basal leaf removal. Am. J. Enol. Vitic.
37:263-268.

144

Wolpert, J.A.,G.S. Howell, and T.K. Mansﬁeld. 1983. Sampling Vidal blanc grapes.
I. Effect of training system, pruning severity, shoot exposure, shoot origin, and cluster
thinning on cluster weight and fruit quality. Am. J. Enol. Vitic. 34:72-76.

Zoecklein, B. 1989. Leaf removal. Vineyard & Winery Information Series. Virginia
Coop. Ext. Service, vol. 4, no.6, pp. 1-9.

CHAPTERIV

Influence of Basal Leaf Removal and Crapping Level on the Fruitfulness of

Primary Buds of Seyval Grapevines. Localized and Positional Treatment Effects.

145

146
Abstract

The removal of leaves at three nodes within the fruiting zone of young potted
(Experiments Iand II) or mature ﬁeld-grown (Experiment III) Seyval grapevines (at
the node of the basal cluster, one node above and one node below that node) had
minimal inﬂuence on ﬂower-bud differentiation for Year 2’ s crop. In particular, leaf
removal at a node had no signiﬁcant effect on the differentiation of the primary bud
developing at that node, despite the evidence (Experiment II) that differentiation was
still underway when leaves were removed, whether at berry pea size or at veraison.
In Experiment II, leaf removal increased the percentage of berry set, berries per
fruitful primary shoot, and berries per cluster in Year 2; yield in Year 2 was not
signiﬁcantly inﬂuenced.

The percentage of fruitful primary shoots and the number of clusters per vine
and per primary shoot in Year 2 were higher on non-bearing (0C1) than on bearing
(3Cl) potted vines (Experiments I and II). The same relationship was found in
Experiment 11 for the number of ﬂowers per cluster and per primary shoot in Year
2; however, the DC] vines had lower percentage of berry set, number of berries per
cluster at harvest and cluster weight than the 3C1 vines, which counteracted the
advantage in cluster number. On mature vines, the percentage of fruitful primary
shoots in 1990 and 1991 (Years 2 and 3) was not signiﬁcantly affected by cropping
level. The unthinned (NT) vines had fewer clusters per primary shoot in 1990 than
the non-fruiting ones; the vines thinned to 1.5 clusters per node retained, had an

intermediate response, not signiﬁcantly different from that of the other cropping

147

levels. A similar but non-signiﬁcant trend was found in 1991. The heavier crop in
1989 than in 1990 may be a reason for a signiﬁcant cropping effect in 1990 but not
in 1991.

The presence of a cluster at a speciﬁc node had no signiﬁcant inﬂuence on
the Year 2 fruitfulness of the primary bud developing at that node, in any of the
experiments. By contrast, bud position on the 6-node cane had a highly signiﬁcant
effect on most fruitfulness responses evaluated. As in previous studies, an increased

fruitfulness from the base to the apex of the 6-node cane was generally found.

Introduction

Seyval (Seyve-Villard 5276) has a propensity to overcrop (Reynolds ct
31,,1986; Kaps and Cahoon, 1989) which is largely due to a high fruitfulness of the
buds at the base of the canes (Pool et 31., 1978) and not counted in balanced-
pruning. To prevent overcropping and reduce the contribution of the non-count crop,
cluster thinning (Fisher et a1., 1977; Reynolds :1 al., 1986; Kaps and Cahoon, 1989)
and cane pruning combined with removal of excess basal shoots (Pool :1 al. , 1978)
have been employed.

Despite overcropping, adequate primary bud fruitfulness is a goal in the
evaluation of new cultural practices. Clusters on primary shoots are heavier than
those on either secondary (Mansﬁeld and Howell, 1981) or non-count shoots (Pool
gt 31., 1978; Wolpert et 31., 1983). Hence, an increased percentage of fruitful primary

shoots may help minimize crop losses following a dormant season in which high bud

148
mortality occurred. Moreover, Wolpert et al. (1983) found that count-crop was of

better quality than non-count crop, although the differences were small.

Light is an important factor for fruitfulness in grapevines (May and Antcliff,
1963; May, 1965; Shaulis :1 31., 1966; Buttrose, 1970, 1974; Shaulis and May, 1971;
Shaulis and Smart, 1974; Kliewer, 1982; Smart e; 111., 1982; Morgan e; a, 1985). An
adequate light microclimate at the basal portion of grapevine shoots will not only
beneﬁt the current season’s but also the following season’s crop, because buds there
will be retained at pruning and produce next season’s crop.

Basal leaf removal can improve the microclimate in the cluster region and
reduce bunch rot (Wolf et a1., 1986; Koblet, 1987,1988;Kliewer and Bledsoe, 1987;
Bledsoe et al., 1988; Smith 91 11., 1988; English :1 31., 1989), with proven economical
advantage on some high value cultivars (Smith et al, 1988). However, leaf removal
has reduced bud fruitfulness (May e1 31., 1969; Mansﬁeld and Howell, 1981; Kingston
and van Epenhuij sen, 1989; Candolﬁ-Vasconcelos and Koblet, 1990), but this is not
a general rule (Kliewer gt 3.1., 1988). The inﬂuence of leaf removal on ﬂower-bud
initiation may be linked to a loss of photosynthate or to a change in the hormonal
balance (Jackson and Sweet, 1972). Carbohydrate accumulation and ﬂower-bud
formation are associated in grapevines (May, 1965; Shaulis and May, 1971; Buttrose,
1974; Winkler er a1., 1974; Bains gt a1, 1981; Smart et al, 1982), although a direct
involvement of carbohydrates has not been proven (W inkler 91 ﬂ. , 1974; Smart :1 a1. ,
1982). Hale and Weaver (1962) suggested that the leaf subtending a bud is the major
source of photosynthate for that bud. Thus, carbohydrate status and bud fruitfulness

may be affected by removing its subtending leaf, unless some compensatory response

149

occurs.

Previously in this research effort, the yield responses of mature, ﬁeld-grown
own-rooted Seyval grapevines to basal leaf removal were investigated (Chapter III).
This study is aimed at providing greater detail concerning the inﬂuence of basal leaf
removal on the reproductive development in Seyval. Toward that end, fruitfulness
responses to leaf removal were assessed for primary buds at speciﬁc node positions
on six-node canes, both on potted and on mature ﬁeld grown-Seyval grapevines

subjected to different cropping levels.

Materials and Methods

BMW
Experiments with Young Potted Vines (Experiments I and 11)

These experiments were conducted at the Horticultural Research Center
(HRC), East Lansing, Michigan, using one-year-old own-rooted Seyval (Seyve-Villard
5-276) grapevines. The vines were weighed and planted in May/1989 (Experiment
I) or in May/1990 (Experiment 11) in 19 1 pots containing a sterilized loam, sand and
peat mixture with good water holding and aeration properties. The potted vines were
placed on a ﬂat gravel-covered area at a 1.0 m x 1.2 m spacing which allowed for
good light exposure, and trained to two shoots. Vines were irrigated, fertilized (using
a Peter’s 20-20-20 solution), and sprayed for pest and disease control as needed.

Cropping level and leaf removal treatments were arranged as a two-factor

factorial, set in a randomized block design; vine fresh weight at planting was used as

 

 

150
the blocking variable. Cropping level was either 0C1 (no clusters per vine) or 3Cl

(three clusters per vine) and was imposed on June 22/ 89, four days before full bloom
(Experiment I), or July 4/90, ten days after full bloom (Experiment 11). On the vines
thinned to three clusters, the basal cluster on one shoot and two clusters (the basal
and the second) on the other shoot were retained.

In Experiment 1, leaf removal levels were: C = no main leaves removed
(control), and R = leaf removal near veraison (August 31/89, nine weeks after full
bloom). In Experiment II an additional leaf removal date was included. Leaf removal
levels were C = control, R1 = leaf removal at pea size (July 27/90, ﬁve weeks after
full bloom), and R2 = leaf removal at veraison (August 21/90, eight weeks after full
bloom). Leaf removal consisted of removing three consecutive leaves in the fruiting
region of both vine shoots. On vines bearing fruit, the leaves opposite, one node
above and one node below the basal cluster were removed. On non-fruiting vines, the
leaves were removed from equivalent node positions. Lateral shoots were removed
at weekly intervals regardless of the treatment combination.

To prevent injury due to naturally occurring freezing temperatures, the vines
in their pots were stored in a controlled temperature room at as 4 °C from late
October until mid May. During storage, the humidity was monitored to avoid tissue
desiceation; molding was prevented by anti-Ms sprays. In May, the vines were
returned to the outdoor gravel pad and both retained canes were pruned to six
nodes. No differential treatments were applied during the second trial year. The
observations on the vines treated in 1989 (Experiment I) ended at three weeks after

bloom in 1990 with the counting of set berries. The vines treated in 1990

 

151
(Experiment 11) were maintained until harvest in 1991; the shoots arising from the

6-node eanes were kept well exposed to sunlight forming a vertical wall supported

by a 3-wire trellis.

Experiment with Mature Field Vines (Experiment III)

Own-rooted, mature, bearing Seyval grapevines planted in 1983 at the
Clarksville Horticultural Experimental Station (CHES), Clarksville, Michigan, were
used. Vine spacing was 2.4 m x 3.0 m within and between rows, and the vines were
trained to Hudson River Umbrella (a bilateral cordon at the top wire) with the top
wire at 1.8 m height and a N -S row orientation. The vines were balanced-pruned
using a 15+10 pruning formula (Reynolds gt 31.,1986) up to a maximum of 65 nodes
retained per vine. A more detailed description of vineyard installation and
maintenance was presented in Chapter 1.

Prior to the 1989 growing season, a randomized block design was established.
Vine size (weight of one-year old cane prunings), which varied between 1.0 and 1.5
kg, was used as the blocking variable. Five blocks of six vines were deﬁned, one vine
per treatment combination.

Leaf removal and cropping level treatments were arranged as a 2x3 factorial.
Leaf removal levels were: C = no leaves nor lateral shoots removed (control); R =
main leaves and lateral shoots removed on all vine shoots at the same three basal
nodes positions defoliated in Experiments 1 and II. Vines were cropped to: 0 = 0
clusters per vine; 1.5 = 1.5 clusters per node retained at pruning; NT = all clusters

retained (no thinning). Lateral shoots were allowed to develop normally, except for

 

152
those at the three treated nodes on defoliated vines.

In the 1990 growing season, each vine was treated as in 1989. Cluster thinning
was done on June l2/89 (one week before full bloom) and June 27/90 (nine days

after full bloom). Leaf removal was imposed on September 10/ 89 (2.5 weeks after

veraison) and August 15/90 (veraison).

(91.1)). .1" :1 or Lu; Olr‘ .0 ° ° .1' a: -0, our m an

Fruitfulness evaluations were done on six, four, and ﬁve replicates (vines) of
Experiments 1, II and 111, respectively, on canes that originated from count nodes,
were well-matured in the fall, and had the position of the nodes that had borne a
cluster or that had been defoliated adequately marked (on fruiting or defoliated
vines, respectively). Cane diameter was smaller on 3C1 than on DC] potted vines
(Chapter I); on mature ﬁeld vines, only canes with medium diameter (7-10 mm
averaged over two perpendicular directions between nodes four and ﬁve) were used.
Canes were pruned to six nodes in May/90 (Experiment I), May/91 (Experiment 11),
April/9O and April/91 (Experiment III). The nodes were numbered from the base
to the apex of the 6-node canes.

Two 6—node canes per vine in the experiments with potted vines and four or
ﬁve 6-node canes per mature ﬁeld vine were used to evaluate the percentage of
fruitful primary shoots relative to the primary shoots evolved, and the number of
clusters (including zero) on the primary shoot (if any) arising from each node
position. On potted vines additional fruitfulness evaluations were performed. In

Experiment I, the number of set berries was assessed at three weeks after bloom on

 

153

every cluster of each primary shoot arising from both 6-node canes. In Experiment
II, the primary shoots arising from one of the 6—node canes (the cane from which
more clusters were originated) were allowed to yield cr0p in 1991. These shoots were
left unthinned while the remaining vine shoots were deblossomed. On every cluster
of the former shoots, the ﬂowers were counted just prior to bloom and the set berries
were counted three weeks after bloom. At harvest (September 3/91), each cluster
was weighed and its berries were counted. The basal cluster of each shoot was

crushed and the seeds were counted to calculate the mean number of seeds per

berry.

5"]!1'

Data (except for binary and ordinal responses) were tested for normality using
the UNIVARIATE procedure of the Statistical Analysis System package (SAS
Institute Inc., 1985a,b). When there was no sufﬁcient evidence for normality of a
given variable, it was brought closer to normality before analysis using the Box-Cox
power transformation with an appropriate power value (Box and Cox, 1964; Draper
and Smith, 1981).

Fruitfulness responses were evaluated on both a whole vine and an individual
bud basis. Data evaluated on a per-vine basis were subjected to analysis of variance
using the GLM (from General Linear Models) procedure of SAS. The factors
included in these analyses were the leaf removal and cropping treatments applied to
the vine in the preceding season; they were analyzed as a two-factor factorial set in

a randomized block design. For a given response, the data relative to all the buds on

154

the 6—node canes retained per vine were combined to give a single observation.

In the analyses of fruitfulness on an individual bud basis, the conditions under
which each speciﬁc node had developed were considered, as well as the treatments
applied to the vine in the previous season. Considered in these analyses were
replicate (REP), cropping level (CROP), leaf removal (DEF), the position of the bud
on the 6-node cane (BP), the presence/absence of a cluster opposite the bud in
question in the season preceding the fruitfulness evaluation (PCL), and the removal
(yes or no) in that season of the leaf (or leaf plus lateral shoot in Experiment III)
that subtended each speciﬁc bud (BDEF). PCL and BDEF were considered nested
within CROP and DEF, respectively. For each fruitfulness response analyzed an
initial, 3 12:19:21 intentionally overparametrized model was deﬁned, which included the
above factors and the interactions that could have some biological meaning. This
model included REP, DEF, CROP, BP, PCL(CROP), BDEF(DEF), DEF*CROP,
DEF'BP, CROP*BP, DEF*CROP*BP, CROP*BDEF(DEF), BP*BDEF(DEF),
DEF*PCL(CROP), and BP*PCL(CROP). Starting with the above model, a backward
elimination procedure was followed, orderly deleting from the model the non-
signiﬁcant interactions (Draper and Smith, 1981). Despite its restrictions (Draper and
Smith, 1981) the backward elimination method was sought as an adequate one, given
its relative simplicity in eliminating the non-signiﬁcant interactions in order to
achieve a more parsimonious model. In the analyses presented, the shootless nodes
were considered as missing. Binary and ordinal responses for the individual buds
were analyzed using the GLIM package (Healy, 1988), assuming the binomial and

the Poisson error distribution, respectively. These responses were, respectively, the

155
fruitful/unfruitful condition of a bud (whether it originated a primary shoot with at

least one cluster or with none), and the number of clusters (zero to four) per primary
shoot. In all the other fruitfulness analyses at the individual bud level, the GLM
procedure of SAS was used and only the fruitful primary shoots were considered.
In the analyses performed with GLM, mean separation tests were done at the
5 % level when the F values were signiﬁeant at 5 % or lower level. The LSD test or
an equivalent test of the GLM procedure for the least-squares means was used,
except for the separation of means for bud position where, due to the large number
of levels, Duncan’s multiple range test was applied. In Experiment H, when leaf
removal was signiﬁcant and was not included in signiﬁcant interactions, orthogonal
contrasts were used to compare the control against the two leaf removal dates, and
also the ﬁrst against the second treatment date; in Experiment III, orthogonal
contrasts were occasionally used to compare the responses of non-fruiting (0) against
those of fruiting (1.5 and NT) vines, and of the 1.5 vines against those of the NT

01188.

Results and Discussion

For the interpretation of the fruitfulness responses, one needs to consider the
stages involved in the ontogeny and development of inﬂorescences and ﬂowers in
grapevines: 1) formation of Anlagen, club-shaped meristematic protuberances arising
from bud apiees, which may or not give rise to inﬂorescence primordia; 2)

differentiation of the Anlagen to form inﬂorescence primordia; and 3) differentiation

 

 

156

of the inﬂorescence primordia to form ﬂowers (see references in Srinivasan and
Mullins, 1981; Swanepoel and Archer, 1988). Stages 1) and 2) occur during the
vegetative season preceding the year of ﬂowering and fruiting. The time of initiation
and the rate of development of an inﬂorescence depend, among other factors, on the
region and the season, the cultivar, the position of the bud on the shoot, and the
position of the inﬂorescence on the condensed shoot within the bud (Pratt, 1971;
Winkler e]; 31. , 1974). The formation of ﬂowers (stage 3) is generally considered to
start after the latent buds are activated the following spring (Pratt, 1971; Buttrose,

1974; Srinavasan and Mullins, 1976; 1978; 1981; Swanepoel and Archer, 1988).

W

Basal leaf removal had little inﬂuence on ﬂower-bud differentiation for the
following season’s crop, whether evaluated at the whole vine (Tables 1, 2, and 3) or
at the individual bud level (Tables 4 to 9).

The reduced number of leaves removed and the timing of removal are
probable explanations for the above results. However, at least in Experiment 11,
inﬂorescence primordia formation was probably not accomplished when leaf removal
was imposed whether at pea size (July 27/90) (R1) or, less predictably, at veraison
(August 21/90) (R2). Evidence for this was obtained from a shading experiment
conducted in parallel with Experiment 11. Vine shading to about 24% of ambient
photosynthetic photon ﬂux starting at one or the other date reduced the percentage
of fruitful primary shoots and the number of clusters per primary shoot in the

following year (Appendix B). Some authors suggested a relationship between shoot

157

Table 1. Influence of 1989 (Year 1) leaf removal and cropping level treatments on the fruitfulness of
potted Seyval grapevines in 1990 (Year 2), evaluated on a vine basis (Experiment I)

 

 

 

 

 

Ito. clusters No. berries set at 3 weeks PFB"
Treatment’ % of
in Year 1 fruitful
1" Vine 1" fruitful 1" fruitful cluster basal
shoots' shoot 1" shoot shoot 1" shoot cluster
Leaf removal
0 60.9 13.0 1.19 1.96 115 195 99 106
R 56.9 11.2 1.01 1.86 99 170 92 97
ns‘" ns ns ns ns ns ns ns
Crop. level
OCl 71.0a 15.23 1.37a 1.96 122a 176 90 93
3Cl 66.7b 9.01) 0.831: 1.86 92b 191 101 109
.‘t m ”t m * M m m
Interaction ns ns ns ns ns ns ns ns

 

’c:control (no leaves retrieved); R:leaves removed on August 31/89 (near veraison)

00l:0 clusters per vine; 3Cl:3 clusters per vine
'Relatively to the total of primary shoots evolved from both 6-node canes retained at prming per vine

‘PFB: post full bloom
'ns, *, '*, m Non significant or significant at 5%, 1% or 0.1% level, respectively

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160

table 3. Influence of 1989 (Year 1) and 1990 (Year 2) leaf removal and cropping level treatments on the
percentage of fruitful primary shoots and on the raster of clusters per shoot in nature field Seyval
grapevines in 1990 (Year 2) and 1991 (Year 3), evaluated on a vine basis (Experth Ill)

 

 

 

 

 

 

 

1990 (Year 2) 1991 (Year 3)
Treatment’ irzitful No. Clusters fraitful Io. Clusters
1" 1"
shoots' 1'" shoot fruitful shoots 1" shoot fruitful
1" shoot 1'w shoot
Leaf removal
0 92.6 1.91 2.05 98.3 2.43 2.47
R 92.3 1.81 1.95 96.1 2.27 2.36
ns' ns ns ns ns ns
Crop. level
0 96.0 2.11a 2.19 98.9 2.50 2.53
1.5 94.1 1.88ab 2.00 98.5 2.34 2.38
NT 87.3 1.59b 1.82 94.2 2.02 2.34
ns * ns ns ns ns
lnteraction ns ns ns ns ns ns

 

'0: control (no leaves removed); R: leaves removed on September 10/89 and August 15/90

0: 0 clusters per vine; 1.5: 1.5 clusters per node retained; NT: unthinned

'Relatively to the total of primary shoots evolved from the 6-node canes retained per vine

'ns, *, **, *** Ion significant or significant at 5%, 1% or 0.1% level, respectively. Mean separation
within columns using the LSD test at 5%.

161

development and the evolvement of the inﬂorescences for the following season’s crop
(Lavec e1 31., 1967 ; Bozhinova-Boneva, 1975). In ‘Alphonse Lavallée’ and ‘Sultana’
grapevines, at least 18 to 21 leaves apical to the examined buds were nwded to
achieve the maximum percentage of differentiated buds at the bud position under
analysis (Lavee e1 31., 1967). The shoot growth of the potted vines in 1990 (Year 1
of Experiment II) was relatively small compared to that in 1989 (Year 1 of
Experiment I) (Chapter I). On August 21/90 there were 19 to 27 nodes per shoot,
with an average of 21 and 24 nodes per shoot on fruiting (3Cl) and non-fruiting (0C1)
vines, respectively (data not shown). The limited 1990 growth conceivably delayed the
development of a sufﬁcient number of leaves to complete ﬂower-bud differentiation,
and inﬂorescence primordia formation was probably scattered over an extended
period.

In all experiments there was a trend for higher percentage of fruitful primary
shoots and number of clusters per primary shoot on control than on vines subjected
to leaf removal (Tables 1, 2 and 3); ﬂower number responded similarly in
Experiment 11. These responses were not statistically signiﬁcant, however. By
contrast, in Experiment II, basal leaf removal increased the percentage of berry set
at three weeks after bloom in Year 2, both at the vine (Table 2) and at the
individual bud level (Table 7); the number of seeds per berry was higher on C and
R1 than on R2 treated vines. On an individual bud basis, additional leaf removal
effects were found on the number of berries per fruitful primary shoot, per cluster
and per basal cluster, both at three weeks post full bloom and at harvest. In each

case, C vines had fewer berries than the vines subjected to leaf removal (Table 7).

 

162

Table 4. Significance’ of the effects of 1989 (Year 1) leaf removal
(DEF), cropping level (CROP), bud position (BP), defoliation at a
specific node (BDEF), presence|of a cluster at a specific node (PCL),
and interactions, on the fruitfulness and yield components of potted
Seyval grapevines in 1990 (Year 2), evaluated on a bt__rd basis
(Experiment I). Mean values for DEF, CROP, and BP levels relative to
these analyses are presented in Table 5.

 

 

 

 

No. No. set berries at 3 weeks PFB'
Factor or clusters
lnteraction per 1" fruitful cluster basal
shoot 1" shoot cluster
DEF ns'I ns ns ns
CROP ** ns ns ns
39 an ass as n
80EF(0EF)" ns ns ns ns
PCL(CROP)‘ ns ns ns ns
059C!!!»
DEF'BP
CRW‘WP
CRW’BDEHDEF)
BP'BDEHDEF)
DEF*PCL(CRN)
BP*PCL(CROP)
DEF*CRW*BP

 

'The level of significance is indicated for the main effects and
interactions present in the final model obtained from backwards
elimination starting at an overparametrized model that contained all
the factors and interactions listed. The main effects were always
kept in the sucessive models, regardless of their significance

'PFB: post full bloom

"ns, *, ”, *** Non significant or significant at the 5%, 1% or 0.1%
level, respectively.

'80EF(0EF): BDEF nested within DEF

”PCL(CRCP): PCL nested within CRW

 

163

Table 5. Influence of bud position and 1989 (Year 1) leaf removal and
cropping level treatments on the fruitfulness of potted Seyval
grapevines in 1990 (Year 2), evaluated on a big basis (Experth I)

 

No. set berries at 3 weeks PFB‘

 

 

Factor Io.
git-”1g: fruitful cluster basal
shoot 1" shoot cluster
Leaf removal'
C 1.19 181 90.4 101
R 1.01 165 88.1 95
ns‘ ns ns ns
Crop. level"
001 1.37s 167 84 93
3Cl 0.82b 182 98 106
** ns ns ns
Bud position
1 0.15 84bc 59c 68b
2 0.28 76c 69bc 70b
3 0.79 116bc 80ab 85ab
4 1.00 133b 83ab 89ab
S 1.94 205a 96a 105a
6 2.22 232a 99a 115a
m m n are

 

'PFB: post full bloom.
'C:control (no leaves removed); R:leaves removed

(near veraison) .

on August 31/89

"ns, *, ”, m Non significant or significant at the 5%, 1% or

0.1% level, respectively. Means for bud position were separated
using Dmcan's New Multiple Range test at the 5% level.

"0Cl:0 clusters per vine; 3Cl:3 clusters per vine.

1691

 

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168
Unexpectedly, potted vines subjected to leaf removal at pea size usually had

intermediate fruitfulness responses between control vines and vines treated at
veraison.

A discrepancy between cluster and ﬂower number on one hand, and the
percentage of berry set and berry number on the other, was also observed in
Experiment 11 when cropping level means were compared. Probable reasons for this
will be discussed in the next section.

To summarize, the data reported for statistically signiﬁcant responses showed
either no negative effects or, in a few cases (related to fruit set in Experiment 11), a
positive leaf removal response. What is a nagging concern, however, are the array of
data suggesting potentially negative responses on ﬂower-bud differentiation, yet non-
signiﬁcant at the a = 0.05 level of probability. Indeed, these data may not represent
real differences. There is also the chance that the differences are real and inadequate
replication has resulted in a Type II statistical error (Steel and Torrie, 1980). This
possibility cannot serve as any weight for this discussion, but should be a

consideration in further effort in this area of Viticultural research.

W

The fruits developing in a given season may inﬂuence bud development and
differentiation for the following season’s crop by competing with the buds for
metabolites or by interfering with the hormonal balance (Jackson and Sweet, 1972).

In this study, as in Antcliff and Webster (1955), ﬂower-bud differentiation for Year

2’ s crop was affected by cropping in Year 1, especially on young potted vines.

169
Potted vines that bore fruit in Year 1 (3Cl) had lower percentage of fruitful

primary shoots and fewer clusters per vine and per primary shoot than non-bearing
(0C1) potted vines (Tables 1 and 2); the number of ﬂowers per primary shoot
(Experiment II) was likewise lower on the 3Cl vines. However, cropping had no
signiﬁcant inﬂuence on the number of clusters per fruitful primary shoot, whether on
potted or on mature vines. Apparently, fruit development in Year 1 reduced the
number of differentiated primary buds, but after the ﬁrst inﬂorescence was formed
within the bud this factor probably had little inﬂuence on the number of
inﬂorescences per bud.

On mature vines, the percentage of fruitful primary shoots (which was higher
than on potted vines) did not signiﬁcantly differ among cropping levels in Years 2
and 3 (1990 and 1991) (Table 3). At the individual bud level, though, cropping in
1989 had a signiﬁcant effect on the fruitful condition of the primary buds in 1990; the
propensity to be fruitful in 1990 was higher for the primary buds on vines that did
not bar fruit in 1989 (O vines) than on fruiting (1.5 and NT) vines (data not shown).
In 1991 the cropping effect was not clearly evidenced, due to signiﬁcant interactions
(data not shown). Cluster number per primary shoot in 1990 was lower on NT than
on O-treated vines; 1.5 vines had an intermediate value, not signiﬁcantly different
from that of 0 and NT vines. Cropping level had no signiﬁcant effect on the number
of clusters per primary shoot in 1991 (Tables 3, 8 and 9).

On mature vines, the differences in response intensity between the two years
under analysis could be due to: a) earlier cluster thinning in 1989 (one week before

full bloom) than in 1990 (nine days after full bloom); hence, the advantage of the

170

Table 8. Significance' of the effects of 1989 (Year 1) and 1990 (Year
2) leaf removal (DEF), cropping level (CROP), bud position (BP),
defoliation at a specific node (BDEF), presence of a cluster at a
specific node (PCL), and interactions, on the number of clusters per
primary shoot of mature field Seyval grapevines in 1990 (Year 2) and
in 1991 (Year 3), evaluated on a ﬁg! ggsis (Experiment lll).ﬂean
values for DEF, CROP, and BP levels relative to these analyses are
presented in Table 9.

 

Factor or lnteraction lo. clusters per primary shoot

1990 (Year 2) 1991 (Year 3)

 

DEF ns' ns

a

crop
or
soertosr)'

8 i! 8
8

rcttcnori'
o£r*cnop
osr*sr
cnorasp
caop*soer<osr)
sp*aosr(oer)
DEF*PCL(CROP)
BP*PCL(CROP)
oar*caor*ap

'ihe level of significance is indicated for the main effects and
interactions present in the final model obtained from backwards
elimination starting at an overparametrized model that contained all
the factors and interactions listed. The main effects were always
kept in the sucessive models, regardless of their significance

'ns, *, **, *** Hon significant or significant at 5%, 1% or 0.1%
level, respectively.

'DDEF(DEF): BDEF nested within DEF

"pcttcaor): PCL nested within CROP

171

table 9. Influence of bud position, and 1989 (Year 1) and 1990 (Year
2) leaf removal and cropping level treatments on the amber of
clusters per primary shoot of mature Seyval grapevines in 1990 (Year
2) and 1991 (Year 3), evaluated on a 99g basig (Experiment Ill)

 

 

 

Factor lo. clusters per primary shoot
1990 (Year 2) 1991 (Year 3)
Leaf removal:' C 2.05 2.43
R 1.90 2.30
ns' ns
Crop. level:‘ 0 2.16 2.51
1.5 1.93 2.34
NT 1.66 2.25
* ns
0 vs. 1.5 and NT *
1.5 vs. IT ns
Bud position: 1 1.78 1.94
2 1.84 1.95
3 1.92 2.24
4 1.92 2.58
5 2.03 2.63
6 2.17 2.63
m **

 

'C: control (no leaves removed),- R: leaves removed on September 10/89
and August 15/90.

'ns, *, **, *** Non significant or significant at 5X, 1% or 0.1%
level, respectively.

'0: 0 clusters per vine; 1.5: 1.5 clusters per node retained; N1:
unthinned.

 

 

buds

stage

basa'

fertii
is p:
bent
the

frorr
relat
set (
Whi<
Clus
of t}

0the

Vine
high
man

who

172

buds developing on non-fruiting vines would have been implemented at an earlier
stage of bud differentiation in 1989. Indeed, the initiation of the ﬁrst Anlage at the
basal bud was found to occur at 12 to 15 days before bloom on ‘Chenin blanc’
grapevines (Swanepoel and Archer, 1988), and an earlier date was suggested by Pratt
(1979) on ‘Concord’; b) heavier crop on 1.5 and NT vines in 1989 than in 1990
(Chapter III); cropping in 1989 would consequently be more depressive to bud
fertility in 1990 than would cropping in 1990 be to bud fertility in 1991. Reason a)
is probably not relevant from the standpoint of competition for photosynthate

between clusters and developing buds. Indeed, Hale and Weaver (1962) found that
the inﬂorescences (clusters) were strong sinks while rapidly increasing in size, but
from about 10 to 14 days before bloom until 10 days after full bloom they were
relatively weak sinks compared to the shoot tip and the parent vine; only after berry
set did the clusters become a powerful sink again, in contrast with the axillary buds,
which were minor sinks. Both in 1989 and 1990, thinning was imposed while the
clusters were conceivably still a weak sink for photosynthate. Thus, if any inﬂuence

of thinning date on bud fertility occurred, it was most probably exerted via a process
other than competition for assimilates.

The lower responsiveness to cropping level of mature as compared to potted
vines was to be expected, not only because the degree of homeostasis is conceivably
higher on the former vines, but also because the canes for fruitfulness evaluation on
mature vines were selected for a deﬁned diameter range (unlike on potted vines
where cane diameter was smaller on 3Cl than on 0C1 vines).

It is important to emphasize that under ﬁeld conditions cropping has an

 

 

 

173
additional, indirect effect, on yield of the following year by inﬂuencing bud burst. The

heavy crop in 1989 not only reduced ﬂower-bud differentiation for 1990 but also
aggravated the primary bud mortality associated with freezing temperatures during
the severe 1989/90 dormant season (Chapter II).

In Experiment 11, ﬂower-bud differentiation and fruit set in Year 2 were not
inﬂuenced in the same manner by the treatments applied in Year 1. In contrast with
the percentage of fruitful primary shoots and the number of clusters and ﬂowers, the
percentage of fruit set in Year 2 was higher on 3Cl than on 0C1 vines (Table 2).
During the massive differentiation to individual ﬂower parts, which occurs shortly
before and after bud-burst (Buttrose, 1974), the inﬂorescence primordia were
conceivably strong sinks. The 0C1 vines, less stressed in Year 1 than the 3Cl vines,
would then have the advantage resulting from greater reserve availability. This may
explain the higher number of ﬂowers per cluster (on an individual bud basis) (Table
7) and, along with more clusters per primary shoot, the higher number of ﬂowers per
primary shoot on DC] than on 3Cl vines (Table 2). The initial advantage of the DC]
vines was probably reduced when the inﬂorescence became a weak sink, including
during the period when most berry set occurred (Hale and Weaver, 1962). Given the
limited capacity of the potted vines (namely those of Experiment II), the markedly
higher number of clusters and of ﬂowers per cluster on 0C1 than on 3Cl vines
conceivably created a stronger competition in the former vines and exerted a
negative inﬂuence on berry set. The number of clusters per fruitful primary shoot was
not signiﬁcantly different on 0C1 and 3Cl vines; however, as suggested by Looney

(1981), within-cluster competition is probably more critical for berry set than

 

 

174

competition among clusters on the same shoot. As both nutritional and hormonal
hypotheses have been proposed for the regulation of berry set in grapevines (Winkler
e1 31, 1974), there is also the possibility that the hormonal balance on 3Cl vines was
more favorable to fruit set than on 0C1 vines. Similar arguments could also explain
the opposite trends in number of ﬂowers and number of berries among control vines
and vines subjected to leaf removal in Experiment II. Yield per primary shoot and
per vine in Year 2 was similar for 0C1 and 3C] vines. The higher number of berries
per cluster on 3C1 than on 0C1 vines contributed to heavier clusters on the former

vines, which compensated for their lower number of clusters (Table 2).

E I E . .

On potted vines, the propensity of a primary bud to originate a fruitful shoot
tended to increase from the base to the apex of the 6-node cane (data not shown).
In Experiment I, the meaning of this observation is restricted due to signiﬁcant
interactions involving bud position (BP), while in Experiment 11 the BP effect was
highly signiﬁcant. However, on mature vines, where a relatively large percentage of
the primary shoots that evolved were fruitful (Table 3), the propensity of a viable
bud to be fruitful was either not signiﬁcantly affected by RP (Year 2) or the BP
effect was confounded by signiﬁcant interactions (Year 3); in both cases this
propensity was relatively uniform along the 6—node cane (data not shown). Whether
on potted or on mature vines, the number of clusters per primary shoot increased
from nodes one to six (Tables 5, 7 and 9). In Year 2, unlike in Year 3 of Experiment

III, this effect was not signiﬁcant, though; this may be due to a lower number of

 

 

obs

inc
fou

wit.

Sam!

(01’ I:

that i

175

observations in the former year, resulting from severe winter damage during the
1989/90 dormant season.

For most of the remaining responses evaluated on potted vines, a gradient of
increasing fruitfulness from the base to the apex of the 6-node canes was usually
found, with only a few minor deviations (Tables 5 and 7). These results are consistent
with the widely reported increase in fruitfulness from the basal to the mid-nodes of
grapevine canes, after which fruitfulness gradually declines towards the apical cane
portion (Partridge, 1921; Buttrose, 1974; Champagnol, 1984; Huglin, 1986; Howell
et a1., 1993). BP had no signiﬁcant inﬂuence on the percentage of berry set and on
the number of seeds per berry, though (Table 7). The lack of a signiﬁcant effect on
the percentage of berry set is understandable given that BP strongly inﬂuenced in the

same direction both the number of berries and the number of ﬂowers per fruitful

primary shoot.

W

The leaf subtending a grapevine bud is probably the major source of
photosynthate for that bud (Hale and Weaver (1962). Alternatively, leaf removal can
alter the pattern of photosynthate translocation in grapevines, originating a
compensatory movement of photosynthate to the treated shoot region (Quilan and
Weaver, 1970). In the present study, the removal of the leaf subtending a given bud
(or leaf plus lateral shoot in Experiment III) (BDEF) had no signiﬁcant effect on the
differentiation of that bud (Tables 4 to 9) despite the evidence (for Experiment 11)

that inﬂorescence primordia formation was still underway when leaves were removed.

 

 

176
A bud whose subtending leaf was removed probably beneﬁtted from a compensatory

photosynthate movement, which may explain the lack of a signiﬁcant reduction in its
fertility. In fruit trees, buds lacking a subtending leaf accumulated l‘C applied to
other leaves on the shoot as readily as did buds with intact leaves (Minnis, 1970),
suggesting that a bud may attract and utilize carbohydrates from a source other than

the subtending leaf (Jackson and Sweet, 1972).

W

The presence of a cluster at a speciﬁc node position in Year 1 (PCL) had no
signiﬁeant effect on the Year 2 fruitfulness responses of the primary bud located at
that node (Tables 4, 6, 8). Grapevine clusters, unlike the inﬂorescences of most
plants, have an extra-axillary, leaf-opposed position on the shoot (hence opposed to
the axillary buds) (Pratt, 1971; Srinavasan and Mullins, 1976). This feature, by itself,
does not prevent the cluster from using carbohydrates or other substances produced
by the opposite leaf. Hale and Weaver ( 1962) found that after berry set the grape
cluster can not only attract photosynthate from the opposite leaf but also divert the
photosynthate moving down the shoot from the originally vertical path. Because of
its polarizing power, a cluster can conceivably affect several axillary buds on the
shoot, besides the one developing on that same node. Conversely, as this study
suggests, the cropping effect on the fruitfulness of a given bud may derive mostly
from the fruiting condition (bearer or not) of the shoot in Year 1, rather than from

the condition (presence/absence of a cluster) of the node where the bud developed.

 

 

177
ET] I . Iﬂn° EIE'EI

In the fruitfulness evaluations at the individual bud level, several signiﬁcant
interactions were observed; to avoid an extensive description, only the most relevant
will be discussed. There were instances, specially in the analyses of the fruitful
condition (differentiated or not) of a primary bud, where some interactions could not
be resolved, because the pattern of the responses resulted in excessively high
variances that compromised the realization of contrasts.

In Experiment II and in Year 3 of Experiment III, the fruitful condition of a
primary bud was inﬂuenced by a signiﬁcant leaf removal x cropping interaction (data
not shown). In Experiment H, leaf removal decreased the propensity of the primary
buds of BC] vines to be fruitful, but had no signiﬁcant effect in the case of 0C1 vines;
this reﬂects the synergism of two negative inﬂuences (leaf removal and cropping)
which by themselves were not signiﬁcantly inﬂuential. As for Year 3 of Experiment
III, contrasts were not feasible; the fruiting propensity of the buds was relatively high
for all treatment combinations but leaf removal appeared to increase that propensity
on non-fruiting vines and to decrease it on NT vines (data not shown). This may be
explained by improved light exposure of the buds on non-fruiting vines resulting from
the removal of their subtending leaf and lateral shoot. Though only well-matured
canes were used in the fruitfulness evaluations, the presence of a lateral shoot (whose
growth was particularly favored on non-fruiting vines) would conceivably affect the
exposure of the bud on the node at which the lateral shoot developed (Howell and

Shaulis, 1980).

 

 

178
Conclusions

Basal leaf removal had little inﬂuence on ﬂower-bud differentiation for the
following season’s crop, whether evaluated at the vine or at the individual bud level.
In particular, the removal of the leaf subtending a bud had no signiﬁcant effect on
the differentiation of that bud. The small number of leaves removed and the timing
of removal are probable explanations for the above results. However, at least in one
experiment with potted vines, there is evidence that inﬂorescence primordia
formation was not yet completed on the 6-node canes when leaf removal was applied
whether at pea size or at veraison.

Cropping in Year 1 inhibited ﬂower-bud differentiation for Year 2’ s crop,
especially on young potted vines. On mature vines, cropping reduced the number of
clusters per primary shoot in 1990 but not in 1991, conceivably due to a heavier yield
(hence stronger inhibition of ﬂower-bud differentiation) in 1989 than in 1990. It must
be noted that under ﬁeld conditions a heavy crop may have a further effect on the
following year’s yield by reducing bud burst, especially if in conjunction with severe
winter conditions as in the 1989/90 dormant season. The presence of a cluster at a
speciﬁc node had no signiﬁcant effect on the fruitfulness of the primary bud
developing at that node, regardless of the experiment. The fruiting condition in Year
1 of the vine or the shoot where the bud developed (bearer or not), rather than the
presence or absence of a cluster at the same node of the developing bud, was
probably the determining factor in the fruitfulness response of that bud to cropping

level. On the other hand, the position of a bud on the 6-node cane had a highly

 

 

179
signiﬁeant effect on most fruitfulness responses. An increasing fruitfulness from the

base to the apex of the 6—node cane was consistently found, in agreement with
previous studies.

Treatment effects on ﬂower-bud differentiation and on fruit set in Year 2
were not in correspondence, as evaluated in one of the experiments with potted
vines. Opposite trends in cluster number on one hand and in the number of berries
per cluster and cluster weight on the other, resulted in a lack of signiﬁcant treatment
effects on yield per vine and per primary shoot in Year 2.

A trend was noticed in all the experiments conducted for higher ﬂower-bud
differentiation on control than on vines subjected to leaf removal; unexpectedly,
though, potted vines subjected to leaf removal at pea size appeared to have
intermediate bud differentiation between control vines and vines treated at veraison.
This trend was not statistically proven in this study. However, its Viticultural interest

suggested that it should be investigated with more detail in future experimentation.

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Bledsoe, A.M.,W.M. Kliewer, and J .J . Marois. 1988. Effects of timing and severity
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Fisher, K.H., O.A. Bradt, J. Wiebe, and V.A. Dirks. 1977. Cluster-thinning ‘de
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Hale, C.R. , and R.J. Weaver. 1962. The effect of developmental stage on direction
of translocation of photosynthate in Vig’s vinifera. Hilgardia 33:89-131.

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Howell, G.S., M.C. Candolﬁ-Vasconcelos, and W. Koblet. 1993. Inﬂuence of
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Jackson, J.E., and GB. Sweet. 1972. Flower initiation in temperate woody plants.
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Kaps, M.L.,and G.A. Cahoon. 1989. Berry thinning and cluster thinning inﬂuence on
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Kingston, C.M.,and C.W. van Epenhuijsen. 1989. Inﬂuence of leaf area on fruit
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Kliewer, W.M. 1982. Vineyard eanopy management - A review. In: Webb, A. D.
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Kliewer, W.M.,and A.M. Bledsoe. 1987. Inﬂuence of hedging and leaf removal on
canopy microclimate, grape composition, and wine quality under California
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Kliewer, W.M.,J.J. Marois, A.M. Bledsoe, S.P. Smith, M.J. Benz, and O. Silvestroni.
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Koblet, W. 1987. Effectiveness of shoot topping and leaf removal as a means of
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Koblet, W. 1988. Canopy management in Swiss vineyards. I_n: Smart, R.E., R.J.
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Looney, N .E. 1981. Some growth regulator and cluster thinning effects on berry set
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Mansﬁeld, T.K., and G.S. Howell. 1981. Response of soluble solids accumulation,
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May, P. 1965. Reducing inﬂorescence formation by shading individual Sultana buds.
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May, P.,and A.J. Antcliff. 1963. The effect of shading on fruitfulness and yield in the
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the Sultana vine. Am. J. Enol. Vitic. 20:237-250.

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SUMMARY AND CONCLUSIONS

On young potted Seyval grapevines, basal leaf removal at berry pea size (ﬁve
weeks after full bloom) increased the net CO; assimilation rate per unit of leaf area
(A), in contrast with leaf removal at veraison, which had no signiﬁcant effect on A
whether on potted or on mature ﬁeld vines. Fruit development enhanced A,
particularly on potted vines. The observed increase in A following a reduction in the
source! sink ratio was probably a consequence of increased photosynthate demand
at individual leaves, as hypothesized by other authors.

On mature, ﬁeld-grown Seyval, the removal of basal leaves and adjacent
laterals at veraison or 2.5 weeks after improved the light microclimate in the cluster
region, with no signiﬁcant negative effects on global vine growth and yield, nor on
the fruitfulness and cold hardiness of the primary buds on the treated shoot region.
Leaf removal reduced cane hardiness in the 1989/90 dormant season. However, the
percentage of nodes evolved in the ﬁeld, which was more consistent with primary bud
than with cane hardiness data (as expected from a higher cold sensitivity of the
primary buds), was not signiﬁcantly affected by leaf removal in any of the trial years.
Similarly, no signiﬁcant adverse effects of basal leaf removal were observed on
potted vines. These results suggest that the use of basal leaf removal to improve
canopy nricroclimate and, thereby, the control of bunch rot W cinema Pers.)
can be broadened to regions where cold injury is an actual concern.

184

 

185
The economical value of basal leaf removal is comprehensibly dependent on

a number of factors inﬂuencing the degree of 39mm infection. Data from ﬁeld-
grown vines supported the view that vines with dense canopies are more likely to
beneﬁt from an improved m control, and less prone to suffer from a potential
loss of carbohydrate due to leaf removal. It could be of interest to increase the
number of basal leaves removed per shoot (to say, ﬁve or six), and assess whether
wmpensatory responses would be implemented and still prevent the expression of
negative effects at the primary bud and whole vine levels.

Fruiting mature vines yielded a heavier crop in 1989 than in 1990. This,
aggravated by an early leaf killing frost in the fall of 1989, may explain the ﬁnding
that cropping in the former year had a stronger impact on cold hardiness, ﬁeld bud
survival, and bud fertility. Mature ﬁeld vines left unthinned in the ﬁrst two (1989 and
1990) trial seasons (NT vines) had lower primary bud hardiness in 1989/90, lower
ﬁeld bud survival in 1989/90 and 1990/91, and fewer clusters per primary shoot in
1990 than non-fruiting (0) ones. The vines thinned to 1.5 clusters per node retained
(1.5 vines) had intermediate values, not signiﬁcantly different from those of NT vines.
Yield was similar for 1.5 and NT vines. The NT vines had lower m infection
in 1989 (presumably due to lower cluster compactness), a prompt growth recovery
by thinning to 1.5 clusters per node retained in the third trial year, and a higher °Brix
in the recovery year than the 1.5 vines. The vine size at the beginning of the
experiment (1.0 to 1.5 kg) appeared to be sufﬁcient to support two consecutive
seasons of unthinning, and balanced-pruning undoubtedly minimized any potential

vegetative/reproductive imbalance resulting from unthinning. These ﬁndings and the

 

 

 

 

186

labor costs of cluster thinning motivate further research on the value of pluriannual
as compared to annual cluster thinning in Seyval.

In this study, there were situations where carbohydrate shortage probably
limited hardiness development and maintenance, while in other instances such a
possibility appeared unlikely. This reinforces the view that by no means should
carbohydrate content be systematically invoked to justify differences in hardiness
degree. Hormonal regulation might have been important in situations where leaf
removal or cropping did not drive carbohydrate levels below a critical point. It would
be of interest to investigate the hypothesis of a hormonal involvement (namely of
ABA) in hardiness responses to basal leaf removal.

During the course of this study, there were a number of trends that
consistently emerged, but lacked statistical signiﬁcance. Their consistency and
viticultural interest suggested that they should be tested in further experiments with
increased number of observations. On mature vines, there was a tendency for leaf
removal to decrease primary bud hardiness in the mid-winter and to increase it in the
early spring, which could have contributed to the lack of a signiﬁcant leaf removal
effect on ﬁeld bud survival through the dormant season. On potted vines, leaf
removal at pea size may have triggered compensatory responses (such as the
observed photosynthetic enhancement and, presumably, an alteration in translocation
patterns), that either did not develop or were less effective when leaf removal was
applied at veraison. This may explain the observation that mid-winter hardiness and
ﬂower-bud differentiation were apparently less affected by leaf removal at pea size

than by leaf removal at veraison. There was no sufﬁcient evidence to corroborate this

 

 

187

trend, however. If real, it would have important viticultural implications, which
motivates further, detailed experimentation. So far, the absence of a signiﬁcant
negative leaf removal effect on the physiological responses analyzed is a point in
favor of leaf removal at pea size relative to removal at veraison given that an earlier
treatment, besides increased easiness of application, is more likely to provide an

effective bunch rot control.

 

 

APPENDICES

APPENDIX A

Inﬂuence of Basal Leaf Removal and Cropping Level on the Stomatal
Conductance, Transpiration Rate, and Water use Efficiency at

Basal, Middle-shoot and Apical Leaves of Seyval Grapevines

 

188
Inﬂuence of Basal Leaf Removal and Cropping Level on the Stomatal

Conductance, Transpiration Rate, and Water use Efﬁciency at

Basal, Middle- shoot and Apical Leaves of Seyval Grapevines

Summary

The effects of basal leaf removal and cropping treatments on gas exchange
were evaluated at basal (BAS), middle-shoot (MID) and apical (AP) leaves of own-
rooted Seyval grapevines, either one-year-old potted vines (Experiments 1, II) or
mature, ﬁeld-grown vines (Experiment III).

Potted vines were trained to two shoots and lateral shoots were removed
weekly. Leaf removal consisted of the removal of three consecutive leaves in the
fruiting region of both vine shoots. On the potted vines used in gas exchange
determinations leaf removal levels were C (control, no leaves removed) and R (leaf
removal near veraison) in Experiment I, or C (control) and R1 (leaf removal at pea
size, 5 weeks after full bloom) in Experiment 11. Cropping level was either 0C1 (no
clusters per vine) or 3Cl (3 clusters per vine) in both experiments. Mature vines,
trained to Hudson River Umbrella (a high bilateral cordon), were cropped at levels
0 (no clusters per vine), 1.5 (1.5 clusters per node retained at pruning) and NT (all
clusters retained, no thinning). Leaf removal levels were C (control), and R (main
leaves and lateral shoots removed at veraison at three consecutive basal nodes on all
vine shoots). Lateral shoots were allowed to develop normally except for those at the

treated nodes of the R treatment vines. Details regarding trial installation and vine

 

 

 

189

maintenance, as well as equipment and procedures used in gas exchange
determinations were described in Chapter I.

The gas exchange parameters measured were net C02 assimilation rate (A),
stomatal conductance (g,), transpiration rate (E) and water use efﬁciency (WUE).
The data herein reported concern the g,, E, and WUE evaluations at the individual
leaf positions on each measurement date and for the combination of the
measurement dates through the season. The responses in A at individual leaves, as
well as in gas exchange parameters for the combination of leaf positions were
presented in Chapter I.

Basal leaf removal at pea size on potted vines (Experiment 11) increased g,,
and E at BAS and MID leaves at either one or both measurements taken in the pre-
veraison period (August 2 and August 9, one and two weeks after leaf removal,
respectively), at the post-harvest measurement, and on average across the
measurement dates following leaf removal (Tables 4 and 5). At AP leaves, this effect
was signiﬁcant only for the measurement taken two weeks after leaf removal. The
observed increase in g,, and E in response to leaf removal is consistent with previous
results (Hunter and Visser, 1988; Candolﬁ-Vasconcelos, 1990). The increase in g,
besides increasing E, is conceivably one reason for the enhanced A at BAS and MID
leaves in response to leaf removal at pea size (Chapter I). On the other hand, leaf
removal at or shortly after veraison whether in potted (Experiment I) or in mature
vines (Experiment III) had no signiﬁcant effect on A (Chapter I), nor on g, and E.
Leaf removal at pea size presumably created a source limitation despite the reduced

number of leaves removed; the observed increase in A, g, and E might have

 

l.- ‘"

 

 

 

190
represented a compensatory response. At veraison, the source/sink ratio was

conceivably less affected by leaf removal, due to a proportionally less important area
and physiological activity of the leaves removed. Moreover, leaf aging might have
prevented a compensatory response to leaf removal at veraison. WUE has been
reported to increase in response to defoliation (Hunter and Visser, 1988; Candolﬁ-
Vasconcelos, 1990). However, no signiﬁcant effect on WUE was found following leaf
removal at pea size (Table 6); leaf removal at or near veraison led to a sporadic
increase in WUE, but this effect was not signiﬁcant when the measurements since
leaf imposition were combined (Tables 3 and 9).

In the experiments conducted, g, and E were generally higher on fruiting than
on non-fruiting vines. At the last measurement in Experiment II, unlike at previous
ones, g, and E were lower at BAS leaves of 3Cl than of 0C1 vines (Tables 4 and 5);
however, at this time the clusters of the BC] vines had already been harvested. These
results are consistent with the cropping level effects on A (Chapter I), which suggest
a photosynthetic enhancement in response to increased sink demand resulting from
fruit development. By contrast, cropping effects on WUE were seldom observed,
regardless of the leaf position, and no consistent pattern was noticed. On average
across sampling dates, the fruiting potted vines in Experiment 11 had higher WUE
at AP leaves than the non-fruiting ones (Table 6), but the opposite relationship was

found at MID leaves in mature ﬁeld vines (Table 9).

 

 

191
Literature cited

Candolﬁ-Vasconcelos, M.C.1990. Compensation and stress recovering related to leaf
removal in Vitis Millika- PhD Diss., Swiss Federal Institute of Technology, Zurich.

Hunter, J .J .,and J .H. Visser. 1988. The effect of partial defoliation, leaf position and
developmental stage of the vine on the photosynthetic activity of ms mm L. cv.
Cabernet Sauvignon. S. Afr. J. Enol. Vitic. 9(2):9-15.

 

table 1.

192

AP leaves of potted Seyval vines (HRC 1989 - Experiment I).

influence of leaf removal and cropping level on the stomatal conductance (g,) of BAS, HID, and

 

 

 

 

9. (Incl CO,.m".s") Average
Leaf Treatment'
position'
June 28 July 11 Aug.21 Aug.25 Aug.30 Sep.12 Sep.18 Over the Since leaf
2 d 2 wk 8 wk V 5 d 2.5 wk 1 wk mole removal
PFB‘ PF8 PF8 PV PV 811 season ieposi t i on
8A8 Leaf removal
c 94.3 75.0 81.4
R 95.7 95.8 95.8
ns‘" ns ns
Crop. level
0151 109.6 131.3 51.41: 70.8b 115.2b 92.8 71.2b 93.4b 78.4
3Cl 119.9 139.4 78.5e 129.3a 166.1a 97.2 99.6e 119.3a 98.8
1'18 m i m i ”8 D *t' ns
lnteraction ns ns ns
HID Leaf removal
c 95.8 88.7 91.0
R 77.9 96.8 90.5
ns ns ns
Crop. level
Del 117.68 57.6 87.31: 121.8b 67.5 68.0b 86.5b 67.8b
3Cl 128.6e 83.1 155.5a 204.7a 106.2 117.5a 125.0a 113.7e
t "S i ﬂ "8 it fit it
lnteraction ns ns ns
AP Leaf removal
c 129.5 108.4 115.4
R 113.4 105.8 108.3
ns ns ns
Crop. level
OCl 76.6 87.8 68.4b 119.9 166.8b 112.5 78.2b 103.5b 89.6b
3Cl 85.4 84.6 104.8e 188.2 220.9a 130.3 135.9a 141.1a 134.0a
m as it "8 * n8 ** it it.
lnteraction ns ns ns
'8As:besal; IIID:middle shoot; AP:apical
'c:control (no leaves removed); R:leaves removed on Aug. 31/89 (near veraison)
001:0 clusters per vine; 3Cl: 3 clusters per vine
'Time in days (:1) or weeks (wk) relative to vine phenophases
PF8: post full bloom; V. Veraison; PV: post veraison; 811: before harvest
'ns, *, '1', m Non significant or signifith at 58.1% or 0.1% level, respectively.

 

 

 

 

193

Table 2. Influence of leaf removal and cropping level on the transpiration rate (E) of 8As,111D, and AP
leaves of potted Seyval vines (NRC 1989 - Experiment I).

 

 

 

E (meal 11,0.m".s") Average
Leaf treatment”
position’
JIM. 28 July 11 Aug.21 Aug.25 Aug.30 Sep.12 Sep.18 Over the Since leaf
2 d 2 wk 8 wk V 5 d 2.5 wk 1 wk mole removal
PFB’l PFB PFD PV PV 81! season i mi ti on
BAS Leaf removal
c 3.47 3.53 3.51
R 3.44 4.24 3.97
ns" ns ns

Crop. level
ocr 4.33 7.10 2.73 2.793 3.333 3.33 3.52 4.133 3.47
3cm 4.33 7.40 3.03 4.34. 4.93. 3.53 4.25 4.37. 4.31

 

ns ns ns ‘* * ns ns m ns
interaction ns ns ns
1110 Leaf removal
c 3.33 3.95 3.74
R 2.98 4.32 3.87
ns ns ns
Crop. level
oct 6.59b 3.09 3.26b 4.08b 2.46 3.42b 3.81b 3.10b
3Cl 6.91a 3.81 4.97a 5.60a 3.85 4.84a 4.89a 4.51s
.8 m 8* *8 m t .08 8*
interaction ns ns ns
AP Leaf removal
c 4.32 4.70 4.57
R 3.94 4.68 4.43
ns ns ns
Crop. level

0C1 3.39 5.29 3.3913 8.20 5.02 3.88 3.87!) [0.321) 3.881)
3Cl 3.75 5.18 8.718 5.53 5.81 [4.37 5.508 5.238 5.138
m m C m m m ** ... m

Interact ion ns ns ns

 

‘BAS:besal; 111D:middle shoot; AP:apical

'C:control (no leaves removed); R:leaves removed on Aug. 31/89 (near veraison)

OCl:0 clusters per vine; 3Cl: 3 clusters per vine

‘Time in days (d) or weeks (wk) relative to vine phenophases

PF8:post full bloom; V:Veraison; PV:post veraison; Blizbefore harvest

'ns, *, i”, m lion significant or significant at 5%, 1% or 0.1% level, respectively.

 

 

194

table 3. Influence of leaf removal and cropping level on the water use efficiency (HIE) of BAS, HID
leaves of potted Seyval vines (NRC 1989 - Experiment I).

 

 

1A5 (ml CO,/mol 11,0) Average
Leaf Treatment'
poeition‘ .
Jme 28 July 11 Aug.21 Aug.25 Aug.30 Sep.12 Sep.18 Over the since leaf
2 d 2 wk 8 wk V 5 d 2.5 wk 1 wk mole removal
PFB' PFB PFB PV PV 8H season iposi t i on

 

8A8 Leaf removal

c 1.98 1.50 1.66
R 2.02 1.36 1.58
ns" ns ns
Crop. level

0C1 2.39 1.71 2.37 2.42a 2.08 2.08 1.45 2.04 1.66
381 2.49 1.68 2.35 1.928 2.17 1.92 1.42 2.00 1.58

ns ns ns * ns ns ns ns ns
Interaction ns ns ns
MID Leaf removal
c 3.01 2.02 2.36
R 2.63 1.82 2.09
ns ns ns
Crop. level
OCI 1.748 2.64 2.72 2.56 3.11 1.89 2.35 2.30
3Cl 1.86a 3.30 2.44 2.68 2.53 1.96 2.46 2.15
* ns ns ns ns ns ns ns
lnteraction ns ns ns
AP Leaf removal
0 2.528 2.04 2.20
R 2.843 1.90 2.21
ee "3 "8
Crop. level

DCl 2.35 1.34 3.02 2.59 2.54 2.75a 2.02 2.32 2.26
3Cl 2.47 1.42 2.84 2.44 2.80 2.61b 1.92 2.30 2.15
ns ns ns ns ns * ns ns ns

Interact i on ns ns ns

 

'8A8:besal; 111D:middle shoot; AP:apical

'c: control (no leaves removed); R: leaves removed on Aug. 31/89 (near veraison)

Del: 0 clusters per vine; 3Cl: 3 clusters per vine

'Time in days (d) or weeks (wk) relative to vine phenophases

“RFD: post full bloom; V. Veraison; PV: post veraison; 811: before harvest

'ns," , ", 1'” lion significant or significant at the 5%, 1% or 0.1% level, respectively.

 

 

195

Table 4. Influence of leaf removal and cropping level on the stoutal corchtance (g,) of BAS, 111D, and
AP leaves of potted Seyval vines (1ch 1990 - Experiment II).

 

 

 

g. (.31 C0,.m".s") Average
Leaf Treatment'
position' .
July 19 July 25 Aug.2 Aug.9 Aug.29 Sep.13 Sep.26 Over the since leaf
3.5 wk 4.5 wk 5.5 wk 6.5 wk 1 wk 1 wk 1 wk whole removal
PFB' PFB PFB PFB PV 811 PH season iuposi t i on
8A5 Leaf removal
C 109.48 118.4 107.6 87.4 37.28 92.08
R1 137.13 126.4 116.7 77.5 52.73 102.13
*' m m m .. *
Crop. level
0C1 165.5 123.6 110.78 115.5 93.68 59.08 52.23 99.78 86.28
3Cl 167.7 136.3 135.93 129.4 130.73 105.93 37.78 118.13 107.93
['18 HS 8 "8 88 88 88 888 888
Interaction ns ns ns ns ns ns
HID Leaf removal
C 105.68 115.78 115.9 104.4 57.78 99.88
R1 148.23 137.13 113.5 97 77.33 114.83
8 88 "s "8 8 88
Crop. level
OCl 112.48 109.18 112.78 98.08 80.18 74.1 97.18 94.88
301 154.53 144.63 140.13 131.43 121.93 61.0 124.33 119.83
8 88 888 88 88 "S 888 888
Interaction ns ns ns ns ns ns
AP Leaf removal
C 70.3 87.08 116.1 114.5 39.1 85.4
R1 88.8 117.83 111.5 101.3 41.6 92.2
ns ** ns ns ns ns
Crop. level
OCl 150.6 89.2 75.6 92.2 98.68 86.68 43.2 88.68 79.28
3Cl 146.3 102.5 83.5 112.7 129.03 129.23 37.5 104.43 98.43
m m 1'18 "8 8 8 718 888 888
Interaction ns ns ns ns ns ns

 

‘8As:8esal; IIID:middle shoot; AP:3pical

'C:control (no leaves removed); R1:leaves removed on July 27/90 (pea size)

OCI:0 clusters per vine; 3Cl: 3 clusters per vine
'Iime in weeks (wk) relative to vine phenophases

PFB. 130“ full bloom; PV: post veraison; 811: before harvest; P11: post harvest

"'ns, ", m Ron significant or significant at the 5%, 1% or 0.1% level,

respectively.

 

 

196

table 5. Influence of leaf removal and cropping level on the transpiration rate (E) of BAS, HID, and
AP leaves of potted Seyval vines (NRC 1990 - Experiment II).

 

 

 

E (sol H,O.m".s") Average
Leaf Treatment'
poeition‘ ’ .
July 19 July 25 Aug.2 Aug.9 Aug.29 Sep.13 Sep.26 Over the since leaf
.5 wk 4.5 wk 5.5 wk 6.5 wk 1 wk 1 wk 1 wk mole removal
PFD' PF8 PFB PFB PV 811 PH season imosi t i on
BAS Leaf removal
C 5.388 5.94 5.05 4.12 1.498 4.408
R1 6.313 6.43 5.36 3.68 2.063 4.773
e" n. m m e :3
Crop. level
0Cl 8.00 6.32 5.36 5.82 4.448 3.008 2.023 4.838 4.138
3Cl 7.98 6.91 6.33 6.55 5.973 4.803 1.528 5.593 5.033
m M "8 m 888 88 8 888 888
Interact i on ns ns ns ns ns ns
HID Leaf removal
C 5.288 5.918 5.34 4.74 2.198 4.698
R1 6.623 6.893 5.36 4.47 2.833 5.233
8 88 n8 "8 8 88
Crop. level
0Cl 5.958 6.543 5.808 4.688 3.838 2.72 4.678 4.488
3Cl 7.483 5.368 7.003 6.013 5.383 2.30 5.713 5.443
888 8 888 88 88 "3 888 888
Interaction ns ns ns ns ns ns
AP Leaf removal
C 3.72 4.798 5.34 5.09 1.60 4.11
R1 4.50 6.003 5.23 4.65 1.68 4.41
ns ** ns ns ns ns
Crop. level
0Cl 7.42 5.04 3.92 4.898 4.728 4.168 1.75 4.438 3.898
3Cl 7.33 5.59 4.31 5.903 5.853 5.583 1.53 5.053 4.633
m 1'18 n5 *3 es eee m eee eee
Interaction ns ns ns ns ns ns

 

'8AS:8asal; HID:middle shoot; AP:apical

'C:control (no leaves removed); R1:leaves removed on July 27/90 (pea size)

0Cl:0 clusters per vine; 3Cl: 3 clusters per vine
'Time in weeks (wk) relative to vine phenophases

PF:8 post full bloom; PV:post veraison; 811: before harvest; P11: post harvest

*, i", *1" Ron significant or simificant at the 5%, 1% or 0.1% level, respectively.

 

 

 

197

Table 6. Influence of leaf removal and cropping level on the water use efficiency (HIE) of BAS, HID,

and AP leaves of potted Seyval vines (HRC 1990 - Experiment II).

 

L f T t' IAIE (not CO,/mol lip)
ea reatmen

Average

 

position'
July 19 July 25 Aug.2 Aug.9 Aug.29 Sep.13 Sep.26
3.5 wk 4.5 wk 5.5 wk 6.5 wk 1 wk 1 wk 1 wk

Over the Since leaf
smole removal

 

PFB' PF8 PFB PFB PV Bil PH season i sposi t i on
BAS Leaf removal
C 2.44 2.29 2.69 2.56 3.30 2.65
R1 2.36 2.35 2.67 2.65 2.88 2.58
nsw ns ns ns ns ns
Crop. level
0Cl 1.50 2.04 2.43 2.44 2.64 2.50 2.83 2.38 2.57
3Cl 1.68 1.94 2.37 2.20 2.72 2.70 3.34 2.47 2.67
ns ns ns ns ns ns ns ns ns
Interaction ns ns ns ** ns ns
HID Leaf removal
C 2.55 2.26 2.64 2.68 3.17 2.66
R1 2.50 2.19 2.68 2.76 3.02 2.63
ns ns ns ns ns ns
Crop. level
0Cl 2.09 2.59 2.25 2.66 2.76 3.02 2.58 2.66
3Cl 2.09 2.46 2.20 2.66 2.69 3.17 2.56 2.63
ns ns ns ns ns ns ns ns
Interaction ns ns ns ns ns ns
AP Leaf removal
C 2.64 2.32 2.25 2.12 2.77 2.42
R1 2.49 2.03 2.18 2.20 2.81 2.34
ns ns ns ns ns ns
Crop. level
0Cl 0.948 1.84 2.45 2.11 2.21 2.04 2.59 2.078 2.288
3Cl 1.283 1.96 2.68 2.24 2.21 2.28 2.99 2.283 2.483
888 "s m "S "s "s ns 88 8
Interaction ns ns ns ns ns ns

 

‘8AS:besal; 111D:middle shoot; AP:apical
'Czcontrol (no leaves removed); R1:leaves removed on July 27/90 (pea size)

0Cl:0 clusters per vine; 3Cl: 3 clusters per vine
'Time in weeks (wk) relative to vine phenophases

PFB: post full bloom; PV: post veraison; 811: before harvest; PH: post harvest

*, I", 1'" Ron significant or significant at the 5%, 1% or 0.1% level, respectively.

198

Table 7. Influence of leaf removal and cropping level on the stontal conrhctance (9.) of BAS, HID, and
AP leaves of nture field Seyval vines (CHES 1990 - Experiment III).

 

 

 

g. (ml C0,.m".s") Average
Leaf position' Treatment'
July 18 Sept. 4 Sept. 25 Oct. 6 Over the Since leaf
4 wk PFB' 3 wk PV ii 10 d P11 whole removal
season imposition
BAS Leaf removal
C 108.1 113.4 83.9 103.4
R 107.1 110.1 79.1 100.5
ns" ns ns ns
Crop. level
0 62.2 95.8 103.8 74.0 86.38 92.88
1.5 71.3 109.2 117.7 86.8 98.73 106.23
RT 70.1 117.8 113.7 83.5 99.93 106.93
ns ns ns ns ** *
Interaction ns ns ns ns
HID Leaf removal
C 126.8 126.3 103.0 120.1
R 121.9 124.2 101.0 117.0
ns ns ns ns
Crop. level
0 74.7 107.0 111.48 105.6 101.08 108.28
1.5 75.6 133.8 130.53 108.5 115.03 125.73
RT 81.6 132.2 133.9 91.9 113.23 121.838
ns C“) " ns * *
lnteraction ** ns ns ns
AP Leaf removal
C 102.6 113.9 117.3 110.7
R 100.6 117.7 99.4 106.5
ns ns ns ns
Crop. level
0 51.28 76.68 102.98 112.5 86.38 95.98
1.5 61.83 112.13 129.73 119.6 108.03 120.53
RT 64.63 116.03 114.938 93.0 99.838 109.338
8 8 8 n8 8 8
mm rs___ns 41.8 m

 

 

‘8AS:8asal; 111D:miﬂle shoot; AP:epicel

'C:control (no leaves removed); R:leaves removed on Aug. 15/90 (veraison)

 

0:0 clusters per vine; 1.5:1.5 clusters per node retained; Nszthimed. Thinning date: Jme 27/90.
'Time in days (d) or weeks (wk) relative to vine phenophases

PF8:post full bloom; PV:post veraison; Il:harvest; Pu:post harvest

'ns, *, 8*, *** Ion significant or significant at 5%, 1% or 0.1% level, respectively. Mean separation

within colt-Is using the LSD test at 5%

 

 

 

199

Table 8. Influence of leaf removal and cropping level on the transpiration rate (E) of BAS, MID, and
AP leaves of mature field Seyval vines (CHES 1990 - Experiment III).

 

 

 

E (moi M,O.m".s") Average
Leaf position’ Treatment'
July 18 Sept. 4 Sept. 25 Oct. 6 Over the Since leaf
4 wk PFD' 3 wk PV ii 10 d PM mole removal
season inposition
SAS Leaf removal
C 5.32 3.32 3.44 4.08
R 5.02 3.06 3.16 3.80
ns" ns ns ns
Crop. level
0 3.42 4.73 2.98 3.07 3.598 3.648
1.5 3.82 5.14 3.34 3.38 3.973 4.013
NT 3.89 5.64 3.27 3.45 4.123 4.183
ns ns ns ns * *
lnteraction ns ns ns ns
MID Leaf rmval
C 6.01 3.56 3.96 4.56
R 5.49 3.35 3.80 4.25
(*) ns ns ns
Crop. level
0 3.99 5.12 3.158 4.03 4.08 4.11
1.5 3.98 5.96 3.5438 3.89 4.40 4.52
NT 4.19 6.16 3.673 3.72 4.50 4.59
ns (**) * ns ns ns
Interaction ** ns ns ns
AP Leaf removal
C 5.08 3.35 4.33 4.25
R 4.78 3.22 3.65 3.91
ns ns ns ns
Crop. level
0 2.888 3.978 3.01 4.15 3.508 3.67
1.5 3.353 5.293 3.56 4.17 4.143 4.35
MT 3.443 5.543 3.30 3.64 4.043 4.21
* * ns ns * ns
Interaction n3 n_sL n3 ns

 

 

‘8AS:8asal; MID:middle shoot; AP:3picel

'C:control (no leaves removed); R:leaves removed on Aug. 15/90 (veraison)

0:0 clusters per vine; 1.5:1.5 clusters per node retained; MT:mthinned. Thinning date: Jme 27/90.
'Time in days (d) or weeks (wk) relative to vine phenophases

PFB: post full bloom; PV: post veraison; II: harvest; PM: post harvest
'ns *, 1", 1"" Mon significant or significant at 5%, 1% or 0.1% level, respectively. Mean separation

within colt-1s using the LSD test at 5%

 

 

200

Table 9. Influence of leaf removal and cropping level on the water use efficiency ONE) of BAS, MID,
and AP leaves of nture field Seyval vines (CHES 1990 - Experiment III).

 

 

 

 

RUE (ml CO, Imol 11,0) Average
Leaf position’ Treetment'
July 18 Sept. 4 Sept. 25 Oct. 6 Over the Since leaf
4 wk PFB' 3 wk PV II 10 d PH whole removal.
season "positron
OAS Leaf rnoval
C 2.24 2.628 1.97 2.30
R 2.22 3.313 1.99 2.55
ns‘” ** ns ns
Crop. level
0 2.86 2.21 3.35 2.37 2.71 2.67
1.5 2.74 2.23 2.82 1.87 2.43 2.35
NT 2.62 2.25 2.72 1.70 2.35 2.27
ns ns ns ns ns ns
Interaction ns ns ns ns
MID Leaf removal
C 2.40 3.47 2.33 2.77
R 2.48 3.75 2.69 3.00
ns ns ns ns
Crop. level
0 2.98 2.57 3.913 2.89 3.11 3.153
1.5 3.26 2.46 3.358 2.37 2.87 2.768
MT 3.05 2.29 3.5738 2.27 2.81 2.758
ns ns * ns ns *
Interaction ns ns ns ns
AP Leaf removal
C 2.37 3.63 2.708 2.92
R 2.23 3.82 3.023 3.02
ns ns ** ns
Crop. level
0 2.79 2.08 3.68 2.90 2.86 2.88
1.5 2.22 2.41 3.73 2.96 2.86 3.04
NT 2.35 2.40 3.78 2.72 2.85 2.99
ns ns ns ns ns ns
Inter£ti_on ns ns ns ns

 

 

 

'8AS:basal; MID:middle shoot; AP:3pical
'C: control (no leaves removed); R. leaves removed on Aug. 15/90 (veraison)

0: 0 clusters per vine; 1. 5: 1. 5 clusters per node retained; MT:mthinned. Thiming date: June 27190.
"Time in days (d) or weeks (wk) relative to vine phenophases

PFC: post full bloom; PV: post veraison; II: harvest; P11: post harvest
'ns,* , ”, m Mon significant or significant at 5%, 1% or D. 1% level, respectively. Mean separation

within colt-ms using the LSD test at 5%

 

 

APPENDIX B

Influence of Vine Shading and Cropping Level on Leaf Gas Exchange,
Vegetative Growth, Dry Matter Accumulation, and Fruitfulness

of Young Potted Seyval Grapevines

201
Inﬂuence of Vine Shading and Cropping Level on Leaf Gas Exchange,

Vegetative Growth, Dry Matter Accumulation, and Fruitfulness

of Young Potted Seyval Grapevines

Abstract

In 1990 an experiment using one-year-old, own-rooted potted Seyval
grapevines was conducted to evaluate the inﬂuence of cropping level and vine
shading to 24 96 of full sun on leaf gas exchange and several vegetative and
reproductive vine parameters.

The presence of fruits increased leaf net CO, assimilation rate (A), stomatal
conductance (g,), and transpiration rate (B) when the measurements across the
vegetative season were considered, but had little effect on water use efﬁciency
(WUE). Shading since berry pea size had no signiﬁcant effect on A at basal (BAS)
and nriddle-shoot (MID) leaf positions, but reduced A at the apical (AP) position
when the measurements following shading were analyzed together; g, and E at BAS
leaves were increased by shading, unlike at the MID and AP positions where no
overall signiﬁcant effect was observed. WUE was reduced by shading; this effect was
highly signiﬁcant at the BAS and MID leaf positions when all measurement dates
were considered.

Shading since pea size increased the total chlorophyll content on a dry weight
basis at veraison and/or at harvest (except for BAS leaves) and reduced the

chlorophyll a/b ratio. Chlorophyll content was higher on fruiting than on non-fruiting

 

202
vines at the AP leaf position. At BAS and MID leaf positions a signiﬁcant cropping

x shading interaction was observed at harvest; the presence of fruits magniﬁed the
shade-induced compensatory increase in leaf chlorophyll.

Cropping level had no signiﬁcant effect on total dry matter accumulation, but
markedly inﬂuenced dry matter partitioning. The fruits developed at the expense of
shoots, roots, and leaves, while trunk dry weight was not signiﬁcantly affected.
Shading increased the percentage of dry matter in leaves in the early fall and
reduced the dry weight of roots and canes when all partitioning dates were
considered. Root dry weight and the sum of the dry weight of roots, canes and trunk
were negatively correlated with the number of days under shading.

Both fruit development and shading in Year 1 reduced the percentage of
fruitful primary shoots and the number of clusters per vine and per primary shoot in
the following year; they increased, however, the number of berries per cluster and
cluster weight. Yield in Year 2 was reduced by shading in Year 1, but did not
signiﬁcantly differ between vines that bore fruit in Year 1 and non-bearing vines.

The presence of a cluster at a speciﬁc node in Year 1 had no signiﬁcant effect
on the fruitfulness of the primary bud developing at that node. In contrast, the
position of the bud on the 6-node cane had a highly signiﬁcant inﬂuence on all
fruitfulness responses analyzed, except for the number of seeds per berry; fruitfulness

generally increased from the base to the apex of the 6-node canes.

 

203
Introduction

The negative effects of shading on grape yield and quality have been widely
reported since the studies of N. J. Shaulis in the mid 60’s (Shaulis et 31., 1966). An
adequate light microclimate at the base of the shoots is of special relevance, because
in this zone are not only the clusters but also the nodes to be retained at pruning
(Shaulis, 1982; Smart et 31.,1990). Shading of this zone, besides affecting wine quality
(see references in Smart at d. , 1990) reduces inﬂorescence initiation, bud burst, fruit
set, berry size (Shaulis and Smart, 1974; Smart :1 3.1.,1990) and tissue cold hardiness
(Shaulis and Smart, 1974; Stergios and Howell, 1977; Howell 91 a1. , 1978; Howell and
Shaulis, 1980; Kliewer, 1982; Wolpert and Howell, 1985; Howell, 1988).

Reduced light is one of the factors that may prevent the photosynthetic
enhancement response to increased sink strength; during an extended period of
cloudy weather or immediately thereafter, when the plant is still carbohydrate
depleted, there may be no detectable difference in the leaf net CO, assimilation rate
(A) between fruiting and non-fruiting plants (Flore and Lakso, 1989).

In this study, the effects of shading and cropping on A and related gas
exchange parameters were investigated at individual leaf positions on fruiting and
non-fruiting potted Seyval grapevines grown under full sun until berry pea size and
thereafter shaded to 24 96 of full sun. Moreover, the inﬂuence of shading post- pea
size or post- veraison on several vegetative and reproductive vine parameters was
evaluated, to complement the information obtained from a parallel leaf removal

study with potted Seyval vines, and from a study with mature ﬁeld Seyval vines where

204
the light microclimate was modiﬁed by differential cropping and leaf removal

treatments.

Materials and Methods

W

This experiment, installed in May/1990, was set and conducted in parallel with
Experiment 11 of Chapters Iand IV at the Horticultural Research Center (HRC) in
East Lansing, Michigan, and used similar one-year-old own-rooted Seyval (Seyve-
Villard 5-276) grapevines. Cultural practices were common to both experiments,
except that shading was imposed instead of leaf removal; cropping level and shading
treatments were applied on the same dates as cropping level and leaf removal in the
parallel experiment. The treatments were likewise arranged in a 3x2 factorial set in
a randomized block design, using vine fresh weight at planting as the blocking
variable. The vines used in this experiment were from the same blocks of those used
in the leaf removal experiment, and the control vines were common to both
experiments. Shading levels were: C = unshaded (control); S1 = shaded starting at
pea size (July 27/90, ﬁve weeks after full bloom); and 82 = shaded starting at
veraison (August 21/90, eight weeks after full bloom). Shading was maintained until
the end of October. Cropping level was either 0Cl (no clusters per vine) or 3Cl (3
clusters per vine) and was imposed on July 4/90, 10 days after full bloom. Treatment
combinations are abbreviated as 000, C/3Cl, Sl/0Cl, Sl/3Cl, SZ/OCl, and S2/3Cl.

Shading was accomplished by placing the vines in a wooden framed shading

 

205

structure built in the same gravel area where the unshaded vines were kept. The
cover and walls of this structure were made of a 73 96 polypropylene black shade
cloth from Chicopee Manufacturing Company (Cornelia, GA, USA). This fabric
transmitted an average of 24 96 of the Photosynthetic Photon Flux (PPF), as
measured with Li-Cor LI-1000 quantum sensors. In a previous study, spectral
measurements through shade fabrics from the same origin and identical to the one
used except for density (92% and 55 % in the manufacturer’s designation) were made
(Long, 1980). None of the fabrics seemed to inﬂuence the spectral distribution within
the range of wavelengths tested ( ~ 380 nm to 1500 nm). Therefore it was assumed

that the fabric herein used was likewise neutral.

W911

The timing of data collection and the methodology used were the same
described for Experiment II in Chapters I and IV, except for the particularities that
follow. The shaded vines were moved to full sun for about 30 minutes prior to gas
exchange determinations; indeed, on the ﬁrst measurement date after shading, a
period of 20 to 30 minutes was found to be needed for the leaves to equilibrate at
their maximum photosynthetic capacity.

In this experiment no carbohydrate analyses were done, unlike in Experiment
II (Chapter I), and fewer fnritfulness parameters were evaluated than in Experiment

II (Chapter IV), because the number of ﬂowers was not assessed.

 

 

206
SHIEI'

Statistical analyses were performed as mentioned for Experiment 11 in
Chapters I and IV , except as described next.

In this experiment the data on dry matter partitioning were further analyzed
by linear regression to test the relationship between the dry weight of the different
vine parts and the number of days of foliage shading (0, 65, and 90 days for C, 82,
and 81 vines, respectively, counted since shading imposition until the ﬁrst leaf killing
frost in the fall).

In the analyses of fruitfulness on a whole vine basis the factors included were
replicate (REP), and the cropping (CROP) and shading (SH) treatments applied to
the vine in the season (Year 1) preceding the fruitfulness evaluation. In the
fruitfulness evaluations on an individual bud basis, two additional factors were
included, to consider the conditions under which each speciﬁc node had developed.
These factors were BP - the position of the bud on the 6-node cane, and PCL - the
presence/absence in Year 1 of a cluster opposite the bud under analysis. PCL was
considered nested within CROP. For each fruitfulness response at the individual bud
level an initial, overparametrized model was set (see Chapter IV), which included the
above factors and the interactions SH*CROP, SH*BP, CROP*BP, SH*CROP*BP,
SH*PCL(CROP), and BP*PCL(CROP). Starting at the above model, a backward
elimination procedure was followed, orderly deleting from the model the non-

signiﬁcant interactions (Draper and Smith, 1981).

 

 

 

207
Results and Discussion

WW
Cropping Level Eﬁ’ects

Cropping level had a highly signiﬁcant effect on the leaf net CO, assimilation
rate (A), stomatal conductance (g,) , and transpiration rate (E) at every leaf position
when all the measurements across the vegetative season were considered. Higher
values were found on fruiting (3Cl) than on non-fruiting (0Cl) vines (Tables 1, 2 and
3), as in the parallel experiment where the potted vines were grown under full
sunlight throughout the whole season (Experiment H of Chapter I). In both
experiments, however, the effects of crOpping on water use efﬁciency (WUE) were
minimal, regardless of the leaf position (Table 4); when the leaf positions were
analyzed together, WUE was higher on 3Cl than on 0Cl vines at 3.5 weeks post full
bloom (Table 5).

Increased A in response to the presence of fruits (and to a decreased
source! sink ratio in general), has been reported in grapevines (Loveys and
Kriedemann, 1974; Kriedemann et 31., 1975; Kriedemann, 1977; Chaves, 1984;
Downton e1 31., 1987) and several fruit crops (Flore and Lakso, 1989), and has been
attributed, among other factors, to increased photosynthate demand; this would
prevent or minimize a hypothesized end-product inhibition of photosynthesis (Neales
and Incoll, 1968). The photosynthetic enhancement may not be observed during or
immediately after an extended period of reduced light levels (Flore and Lakso, 1989).

However, the shading intensity applied in this experiment was not sufﬁcient to

208

Table 1. Influence of shading and cropping level on the net CO2 assimilation rate (A) of SAS, MID, and

AP leaves of potted Seyval vines (NRC 1990).

 

 

 

A (mmol co,.m".s") Average
Leaf ' Treatment' .
”Rh" July 19 July 25 Aug.2 “.9 Aug.29 Sep.13 Sep.26 Over the Since
3.5 wk 4.5 wk 5.5 wk 6.5 wk 1 wk 1 wk 1 wk smole shading
PFB' PF8 PFB PFI PV 811 P11 season iupoai t ion
8A8 Shading
C 13.10 13.16 13.413 10.66 4.56 10.98
SI 14.51 13.98 11.138 9.87 6.81 11.00
ns' ns * ns P“) ns
Crop. level
0Cl 11.90 12.75 12.74 13.54 11.48 8.20 5.19 10.818 10.108
3Cl 12.51 13.29 14.42 13.60 13.06 12.33 6.18 12.183 11.853
"8 m "8 n. m (88’ (8) 88 888
Interaction ns ns ns " ** ns
MID Shading
C 13.32 13.158 13.903 12.553 6.69 11.92
$1 15.26 13.863 10.928 10.568 7.27 11.17
118 8 88 88 "8 "8
Crop. level
0Cl 12.59 12.78 12.30 11.218 10.138 7.33 11.018 10.648
3Cl 15.14" 15.16 14.71 13.613 12.983 6.64 12.993 12.483
08 1'18 1'18 8 88 m 888 888
Interaction ns ns ns ns ns ns
AP Shading
C ' 9.63 10.76 11.933 10.86 4.50 9.543
S1 8.22 10.52 8.138 7.22 3.82 7.518
"S n5 8 88 "s 888
Crop. level
0Cl 6.978 9.91 7.99 9.028 8.418 6.968 3.82 7.608 7.208
3Cl 9.143 11.11 10.34 12.263 11.653 11.123 4.51 10.013 9.963
8 m m 88 8 88 m 888 888
Interaction ns ns ns ns ns ns

 

‘8AS:besal; MID:middle shoot; AP:apical
'C: control (mahaded); S1: shaded since July 27/90 (pee size)

0Cl: 0 clusters per vine; 3Cl: 3 clusters per vine
'Time in weeks (wk) relative to vine phenophases

PFC: post full bloom; PV: post veraison of C vines; 811: before harvest; P11: post harvest
"ne, 8, i", m Mon significant or significant at the 5%, 1% or 0.1% level, respectively. Brackets
indicate that the factor is involved in a significant interaction; therefore no mean separation was

performed for the main effect.
'Almost simificant at the 5% level (P80. 0567)

 

 

209

Table 2. Influence of shading and cropping level on the stoemtal contArctence (9.) of SAS, MID, and AP
leaves of potted Seyval vines (HRC 1990).

 

 

 

g, (mnol CO,.m".s") Average
Leaf Treatment' ,
position' July 19 July 25 A .2 Aug .9 Aug-29 SOP-13 SOP-25 0"” "‘9 Since
3..5wk45wk 5.5wk6.5wk1wk 1wk 1wk whole shading
"8' PFC PFC PF 8 PV 811 P11 season imosition
CAS Shading
C 109.4 118.4 107.6 87.4 37.2 92.08
Si 135.0 120.3 98.2 96.0 77.4 102.93
ns" ns ns ns (***) "
Crop. level
0Cl 165.7 122.2 106.1 117.4 90.78 72.38 50.8 104.98 86.58
3Cl 167.1 137.6 130.5 121.3 115.23 111.23 63.8 121.93 107.83
"8 ns 03 OS 8 88 "S 888 888
Interact i on ns ns ns ns *“ ns
MID Shading
C 105.6 115.7 115.93 104.4 57.7 99.8
$1 124.6 114.8 94.58 98.1 76.8 99.2
ns ns * ns ns ns
Crop. level
0Cl 117.38 92.58 98.38 92.88 78.88 71.9 92.48 86.68
3Cl 149.73 131.33 132.23 117.63 123.73 62.6 119.63 112.53
8 8 88 8 888 "S 888 888
Interact i on ns ns ns ns ns ns
AP Shading
C 70.3 87.0 116.13 114.5 39.1 85.4
S1 59.5 89.4 79.68 103.9 41.7 76.5
ns ns * ns ns ns
Crop. level
0Cl 139.8 88.8 58.5 70.58 76.28 82.78 37.2 81.18 65.48
3Cl 146.5 105.7 74.8 105.93 119.63 135.73 43.6 106.43 97.03
m "s M 8 88 888 m 888 888
Interaction ns ns ns ns ns ns

 

 

 

 

'CAS:basal; MID:middle shoot; AP:apical
'C: control (unshaded); S1: shaded since July 27/90 (pea size)

0Cl: 0 clusters per vine; 3Cl: 3 clusters per vine
”Time in weeks (wk) relative to vine phenophases

PFC: post full bloom; PV:post veraison of C vines; 811: before harvest; P11: post harvest

'ns, *, '1', 1'” Mon significant or significant at the 5%, 1% or 0.1% level, respectively. Brackets
indicate that the factor is involved in a significant interaction; therefore no mean separation was
performed for the min effect.

210

Table 3. Influence of shading and cropping level on the transpiration rate (E) of CAS, MID, and AP
leaves of potted Seyval vines (11RC 1990).

 

 

 

E (maol 11,0.m".s") Average
Leaf . Treatment'
ition .
pee July 19 July 25 Aug.2 Aug.9 Aug.29 Sep.13 Sep.26 Over the Since
3.5 wk 4.5 wk 5.5 wk 6.5 wk 1 wk 1 wk 1 wk whole shading
PFC' PFC PFC PFC PV C11 P11 season iuposi ti on
CAS Shading
C 5.38 5.94 5.05 4.12 1.49 4.408
S1 6.72 6.58 4.89 4.36 2.86 4.953
1'18. m T18 118 (see) ea
Crop. level

Oct 7.98 6.34 5.40 6.17 4.368 3.528 2.01 5.188 4.238
3Cl 7.91 6.87 6.32 6.34 5.583 4.963 2.33 5.813 5.083

"8 "S n8 m 88 88 n8 888 888
Interact i on ns ns ns ns *" ns
1110 Shading
C 5.28 5.91 4.74 4.74 2.19 4.69
SI 6.37 6.32 5.36 4.33 2.89 4.77
ns ns ns ns ns ns
Crop. level
0Cl 6.208 4.978 5.468 4.428 3.748 2.71 4.608 4.228
3Cl 7.263 6.323 6.773 5.653 5.333 2.36 5.623 5.233
8 8 88 88 888 1'18 888 888
Interaction ns ns ns ns ns ns
AP Shading
C 3.72 4.79 5.343 5.09 1.60 4.11
51 3.60 5.18 4.028 4.48 1.62 3.80
ns ns * ns ns ns
Crop. level

081 7.06 5.06 3.24 4.218 3.808 3.918 1.51 4.218 3.378
3Cl 7.27 5.63 4.13 5.763 5.563 5.663 1.72 5.193 4.593

m m m 8 88 888 1'18 888 888

Interaction ns ns ns ns ns ns

 

'CAS:8esal; MID:middle shoot; AP:apical
'C:control (mshaded); S1:sh3ded since July 2719!) (pea size)

0Cl:0 clusters per vine; 3Cl: 3 clusters per vine
'Time in weeks (wk) relative to vine phenophases

'P:FC post full bloom; PV: post veraison of C vines; C11: before harvest; P11: post harvest

'ns, *, “, *** Mon significant or significant at the 5%, 1% or 0.1% level, respectively. Brackets
indicate that the factor is involved in a significant interaction; therefore no mean separation was
performed for the main effect.

211

Table 4. Influence of shading and crowing level on the water use efficiency (lRJE) of CAS, MID, and
AP leaves of potted Seyval vines (NRC 1990).

 

IAJE (Incl CO,lmol 1110) Average
Leaf Treatment'
position’

 

July 19 July 25 Aug.2 Aug.9 Aug.29 Sep.13 Sep.26 Over the Since
3.5 wk 4.5 wk 5.5 wk 6.5 wk 1 wk 1 wk 1 wk whole shading

 

PFC' PFC PFC PFC PV C11 P11 season iuposi t i on
CAS Shading
C 2.44 2.29 2.693 2.56 3.303 2.653
S1 2.19 2.14 2.308 2.30 2.448 2.288
m” m 8 m 8 888

Crop. level
0Cl 1.49 2.01 2.40 2.27 2.64 2.32 2.64 2.23 2.46
3Cl 1.59 1.94 2.30 2.16 2.35 2.53 3.09 2.26 2.49

 

ns ns ns ns ns ns ns ns ns
Interaction ns ns ns * ns ns
MID Shading
C 2.55 2.26 2.643 2.68 3.17 2.663
S1 2.45 2.21 2.318 2.49 2.62 2.418
ns ns * ns ns **
Crop. level
0Cl 2.03 2.61 2.30 2.54 2.723 2.80 2.48 2.59
3Cl 2.09 2.42 2.17 2.42 2.458 2.99 2.42 2.49
ns ns ns ns * ns ns ns
Interaction ns ns ns ns ns ns
AP Shading
C 2.64 2.32 2.25 2.123 2.77 2.42
51 2.40 2.06 2.01 1.608 2.68 2.34
ns ns ns *** ns ns

Crop. level
0Cl 0.998 1.98 2.59 2.22 2.19 1.76 2.67 2.02 2.27
3Cl 1.263 1.98 2.53 2.15 2.07 1.96 2.78 2.08 2.29
* ns ns ns ns ns ns ns ns

lnteracti on * ns ns ns ns ns

 

‘CAS:basal; MID:middle shoot; AP:apical

'C: control (mshaded); S1: shaded since July 27/90 (pee size)
081:0 clusters per vine; 3Cl: 3 clusters per vine

'Time in weeks (wk) relative to vine phenophases

PFC: post full bloom; PV: post veraison of C vines; 811: before harvest; P11: post harvest
“'ns, *, “', ”1' Mon significant or significant at the 5%, 1% or 0.1% level, respectively.

 

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213

prevent a cropping effect on A, although at BAS leaves (and, to a lesser extent, at

MID leaves) this effect was less marked than in Experiment II of Chapter I.

Shading Eﬁ’ects

When the measurements after shading were analyzed together, shading had
no signiﬁeant effect on A at the BAS and MID leaf positions, but had a highly
signiﬁeant negative effect on A at AP leaves (Table 1). Shading increased g, and E
at the BAS leaf position, unlike at the MID and AP leaf positions, where no
signiﬁcant effect was observed on average across measurement dates (Tables 2 and
3). WUE was reduced by shading; this effect was highly signiﬁcant at the BAS and
MID leaf positions when the measurement dates following shading were combined
(Table 4).

Reduced light conditions decrease the activity of Rubisco (ribulose-1,5-
bisphosphate carboxylase) , not only because the production of ribulose bisphosphate
depends upon the production of ATP and NADPH, but also due to reduced Rubisco
regeneration and to regulatory mechanisms of the enzyme’s activity (Robinson, 1986;
Seemann, 1989). A signiﬁcant negative shading effect on A was not observed at any
leaf position, though, until the measurement of August 29. At this time A was lower
on 81 than on C vines at every leaf position (Table 1), and the same was found for
A, g,, and B when all the leaf positions were analyzed together (Table 5).
Interestingly, at the ﬁrst two measurements following shading (August 2 and August
9, one and two weeks since shading imposition) there was a tendency for higher A

at the BAS and MID leaf positions of 81 as compared to C vines, which was

 

 

 

214

signiﬁcant for MID leaves on August 9.

Shading x Cropping Level Interaction

One week before harvest, A at the BAS leaf position was inﬂuenced by a
signiﬁeant shading x cropping interaction; the same was observed at this leaf position
for A, g., and E
on the last measurement date, one week after harvest (Fables 1, 2 and 3); a
signiﬁcant interaction was likewise observed at the BAS leaf position at one week
before harvest. At one week before harvest, the presence of fruits increased A at
BAS leaves of C but not of 81 vines; among C vines, A was about 95% higher on 3Cl
than on 0Cl vines, while among 81 vines the difference was only of 15 % (data not
shown). At this time, A was higher at BAS leaves of 030 than of Sl/3Cl vines. On
C/3Cl vines, however, A, g, and E declined sharply from one week before to one
week after harvest, while on Sl/3Cl vines the decline was slight. At one week after
harvest A, g,, and E at BAS leaves were not signiﬁcantly different on 030 and
C/OCl vines, but were higher on Sl/3Cl than on Sl/OCl vines, and on Sl/3Cl than
on C/3Cl vines (data not shown). It seems therefore, that at the BAS leaf position
of 3Cl vines, shading reduced the enhancement of A in response to cropping, but
prevented a dramatic decline in A after harvest. Decreased A following harvest has
been attributed to increased source/ sink ratio, which could lead to end-product
inhibition of photosynthesis (Neales and Incoll, 1968). Moreover, fruit removal was
found to increase the concentration of abscisic acid in the leaves (Loveys and

Kriedemann, 1974), and this would reduce g, and A (Loveys and Kriedemann, 1974;

 

 

 

     

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,..\.J —

 
 

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215
Downton et 31., 1988). On C, unlike on 81 vines, fruit removal probably resulted in

a marked raise in leaf ABA, which could explain the sharp decrease in g, and A from
the pre- to the post-harvest measurements observed on the former but not on the
latter vines. An increase in an ABA precursor might have occurred on 81 vines;
however, based on Burden e1 31. (1971), light would be needed for its conversion into
ABA. Higher chlorophyll concentration in the BAS leaves of S l/3Cl relative to
C/3Cl vines, as will be discussed further on, may further explain the higher A of the

former leaves at the post harvest measurement.

Exposure During and Aﬂer Leaf Development

Differences in leaf age and in light conditions during leaf development may
have accounted for the differences in gas exchange responses to shading and cropping
level among leaf positions. The BAS leaves measured on 81 vines were already fully
expanded when the vines were transferred to shading conditions. The same is true
for the MID leaves on the ﬁrst two measurements following shading, while those
used thereafter had a successively longer period of growth and development under
shade. The AP leaves, however, accomplished either most or all of their expansion
under shading. The activity of Rubisco was probably more affected by shading at AP
than at BAS and MID leaf positions. Moreover, photoinhibition (Powles, 1984) might
have occurred on 81 vines due to high radiation levels (PPF above 1000 umol m’zs")
during the gas exchange evaluations, and the AP leaves were conceivably more
sensitive than BAS and MID leaves. The above may explain the fact that at AP but

not at BAS and MID leaves, shading reduced A when the measurements after

 

 

 

216

treatment were combined, and the tendency for a shade-induced decrease in A was
observed since the ﬁrst measurement after shading (Table 1). Even though the BAS
leaves were expanded before transfer to shade, they still experienced (though less
markedly than MID and AP leaves) changes in leaf chlorophyll and in speciﬁc dry
weight induced by shading (Table 6). This agrees with the results of Barden (1974)

in apple trees.

Wm

Adaptation to reduced light environments involve several morphological,
physiological, and biochemical changes (Berry, l975;Bjorkman, 1981; Seemann, 1989;
Knapp and Smith, 1990). Shading increased the chlorophyll content per unit of dry
weight of AP leaves both at veraison and at harvest, and of MID leaves at veraison
(Table 6). In MID leaves, however, the chlorophyll content at harvest was lower on
81 than on C vines, if expressed on a leaf area basis. This reflects a shade-induced
reduction in speciﬁc leaf weight, which was highly signiﬁcant at every leaf position,
and particularly marked for MID leaves at harvest. Shade-induced changes in leaf
chlorophyll probably took place soon after treatment imposition; this may explain the
delayed decrease in A following shading, and the higher A at MID leaves of 81
relative to C vines two weeks after treatment. Chlorophyll changes could not prevent,
however, the occurrence on August 29 and September 13 of lower A on 81 vines
(Table l). Fruiting vines had higher chlorophyll content than non-fruiting ones at the
AP leaf position both at veraison and at harvest and, on a leaf area basis, at the MID

position at harvest. The chlorophyll concentration in MID (on a dry weight basis) and

217

Table 6. Influence of shading and cropping level on the total chlorophyll content, chlorophyll_a/b
ratio, and specific leaf ueidnt (81.11) of BAS, H10 and AP leaves of potted Seyval vines at veraison
(Aug. 24) and at harvest (Sept. 19) (Hill: 1990).

 

Total chlorophyll (chl a r b)

 

 

 

Leaf Treatnent' chlorophyll a/b SLH (mg/cal”)
pooition' w:
Veraison‘l Harvest Veraison Harvest Veraison Harvest Veraison Harvest
BAS Shading
c 43.52 29.10 7.00 4.42 4.17 3.36a 6.22a 6.62s
51 48.36 34.77 9.00 6.42 3.90 2.991: 5.241: 5.461:
"8" (it ) m (it! ) "8 t *tt tit
Crop. level
Oct 46.10 29.25 8.01 4.82 4.09 3.29 5.87 6.13
3Cl 45.77 34.62 8.22 6.02 3.98 3.06 5.59 5.95
ns t") ns C“) no ns ns ns
Interact i on ns 8* ns ** ns ns ns ns
H10 Shading
C 46.54 35.84a 7.71b 5.63 4.28a 3.68a 6.06a 6.39a
31 49.63 28.78b 12.78a 9.11 3.75b 3.00b 3.96b 3.26!)
ns aaa an (easy) as one aaa one
Crop. level
00l 46.04 30.551: 9.50 6.39 4.02 3.37 5.14 5.03
301 50.13 34.08a 11.00 8.36 4.01 3.31 4.89 4.62
ns * ns 0*) ns ns ns ns
Interact i on ns ns ns * ns ns ns ns
AP Shading
c 27.71 14.75 6.78!) 3.10b 3.59 3.50 4.08a 4.88s
81 24.92 15.83 13.01a 5.66a 3.50 2.86 2.41b 2.93b
ns ns t" it ns "8" t** it!
Crop. level
OCl 23.13b 13.14!) 9.14b 3.26b 3.55 2.97 3.31 4.26a
3Cl 29.49a 17.43a 10.65a 5.49a 3.53 3.39 3.19 3.54b
* t it it "8 m m m
lnteraction ns ns ns ns ns ns ns ns

 

‘8AS:basal; MID:middle shoot; AP:apical
'c:control unshaded); S1:shaded since July 27/90 (pea size)
00l:0 clusters per vine; 3Cl: 3 clusters per vine
‘Relatively to unshaded (C) vines
'ns, *, **, m Hon significant or significant at the 5%, 1% or 0.1% level, respectively. Brackets

indicate that the factor is involved in significant interactions; therefore no mean separation was
perforned for the nain effect.

'Alnost

significant

at

the

5%

level

(P80.0517)

 

 

218

BAS leaves at harvest was inﬂuenced by a signiﬁcant cropping x shading interaction.
Mean comparison among treatment combinations revealed that the presence of fruits
intensiﬁed the shading-induced increase in leaf chlorophyll. Indeed, the difference
in total chlorophyll content between Sl/OCl and C/OCl vines was signiﬁcant at the
5% level for MID leaves but not signiﬁcant (though also positive) for BAS leaves,
while a highly signiﬁcant positive difference between Sl/3Cl and C/3Cl was found
at both leaf positions (data not shown). Shading decreased the chlorophyll a/b ratio.
This effect was highly signiﬁcant for MID leaves on both measurement dates, and
signiﬁcant or almost signiﬁcant (P = 0.0517) for BAS and AP leaves, respectively,
at harvest. The lower chlorophyll a/b ratio on 81 vines may reﬂect a proportionally

higher contribution of the light-harvesting complex to the total chlorophyll

complement of the chloroplast (Bj orkman, 1981).

 

In this experiment, as in Experiment II of Chapter I, the fruiting (3Cl) vines
had lower number of leaves (nodes), area per leaf and, consequently, total leaf area,
than the non-fruiting (0Cl) ones; no signiﬁcant differences in the overall speciﬁc leaf
weight were observed (Table 7). The length of shoots and intemodes was inﬂuenced
by a signiﬁcant shading x cropping level interaction. The comparison of treatment
combination means revealed that both on 0Cl and 3Cl vines, shoot and intemodc
length were higher on vines shaded since pea size (81) than on control (C) vines; on
DC] vines the means for the three shading levels were clearly separated, while on 3C1

vines no signiﬁcant differences in shoot and intemode length were found between

 

 

 

219

Table 7. Influence of shading and cropping level on shoot growth parameters, leaf area, and specific
leaf weidit of potted Seyval grapevines (Hill: 1990).

 

 

Total shoot Ho. of Internode Diameter Total leaf Single Specific
Trutnent' length/vine nodes] length of 5'” areg/vine leaf area leaf
(ea) Ivine (on) intemodc (an i (en’) weight
(In) (us/ca”)
Shading
C 198.3 52.1 3.8 5.8a 3292.51.) 65.8b 6.42s
S1 317.8 56.2 5.6 4.7c 5021.6a 92.8a 4.12c
82 256.1 56.5 4.4 5.3b 4001.6ab 75.31: 4.971)
(tit )V n8 (9..) "t it *** “t
c V3. “M if. ﬁt it. it.
S1 vs. 82 ** ns ** ***
Crop. level
OCl 314.0 60.4a 5.1 5.9a 4877.3a 85.4a 5.12
301 200.8 49.4b 4.0 4.6!: 3518.5b 72.7b 5.17
(0“) one (one) m t” t “8
Interaction * ns * ns ns ns ns

 

‘c:control (mshaded); S1:shaded since July 27/90 (pea size); $2:shaded since Aug.21/90 (veraison)
OCl:0 clusters per vine,- 3Cl: 3 clusters per vine
'ns, *, ", m Hon significant or significant at 5%, 1% or 0.1% level, respectively.

Mean separation within column using the LS!) test at 5%. Brackets indicate that the factor is
irfnfrolitted in simificant interactions; therefore no mean separation was performed for the main

e ec .

220

vines shaded since veraison (82) and control vines (data not shown). Shoot diameter
was highly signiﬁeantly reduced by fruit development and by shading. Shaded vines
had larger total leaf area and area per leaf than the unshaded ones but lower speciﬁc
leaf weight; the number of leaves (nodes) was not signiﬁcantly affected by shading
(Table 7).

As in Experiment II of Chapter I, cropping level had a signiﬁcant effect on
dry matter allocation but not on total dry weight at the end of the vegetative season
(September 30); this is consistent with the results of Eibach and Alleweldt (1985) and
Edson (1991). The fact that the total dry matter accumulation was similar in fruiting
and non-fruiting potted vines may be viewed as a rough indication of a lack of
photosynthetic response to cropping at the whole vine level, in contrast with the
enhancement of A by fruiting at individual leaf positions. Similarly, Edson (1991)
found that A at individual leaves responded positively to an increased cropping level,
but there was no signiﬁcant correlation between cropping level and net CO,
assimilation rate of the whole vine; he concluded that the lower A on slightly
cropped vines was compensated for by the larger leaf area of these vines.

At the end of the season, the fruits represented 39% of the overall mean dry
weight of 3Cl vines. The presence of fruits resulted in a signiﬁcant decrease of about
70%, 39%, and 37% in the dry weight of canes, roots and leaves, respectively. By
contrast, the trunk dry weight was not signiﬁcantly affected by cropping level (Table
8). At this time, no signiﬁcant shading effect on the dry weight of the different vine
parts was found, but the percentage of dry matter in leaves was higher on shaded

than on control vines, and the percentage of matter in canes was higher on 81 than

221

Table 8. Influence of shading and cropping level in 1990 on the dry weight partitioning of potted
Seyval grapevines at the end of the season (Septwer 30/90).

 

 

 

 

Dry weight (g) Total Percent of total dry weight
Treat-ent' dry
Fruits Leaves Canes Trail: Roots :39.“ Fruits Leaves Canes T rmk Roots
Shading
c 31.8 24.6 26.3 13.8 41.8 138.2 21.7 17.8b 19.1b 10.9 30.5
S1 18.2 25.8 28.7 11.1 28.9 112.6 17.9 22.5a 23.9a 9.9 25.7
52 20.5 24.7 22.1 16.8 33.2 117.4 18.9 20.9ab 18.2b 14.2 27.8
ns' ns ns ns ns ns ns ** * ns ns
c vs. shaded *‘ ns
51 vs. $2 ns *
Crop. level
001 0b 31.2a 39.6a 14.2 42.6a 127.6 0a 24.4a 30.7a 11.5 33.3a
301 47.0a 18.9b 11.8b 13.6 26.7b 118.0 39.0b 16.4b 10.0b 11.8 22.7b
”t it m m t m m ”i m "8 m
r on ns ns ns ns ns ns ns ns ns

‘c:control unshaded); $1:shaded since July 271% (pea size); S2:shaded since Aug.21/90 (veraison)
001:0 clusters per vine; 3Cl: 3 clusters per vine

'ns, *, V“, m Hon signifith or signifith at the 5%, 1% or 0.1% level, respectively. Hean
separation within colums using the LSD test at 5%

Table 9. Influence of shading and cropping level during the 1990 season on the dry weight of canes,
trmk and roots of potted Seyval grapevines, on average across partitioning dates in the fall and
winter of 1990/91.

 

 

 

Dry weight (9)
Treatnent'
Canes Trail: Roots Total of the
three vine parts
Shading: c 34.5a 13.2ab 42.8a 90.5a
s1 28.7ab 10.7b 25.9b 65.2b
$2 26.1b 14.5a 31.0b 71.6b
*V t it. it.
C vs. shaded * ns *** *"*
S1 vs. S2 ns ** ns ns
Crop. level: 001 44.7a 13.5 40.5a 98.7a
3Cl 14.81) 12.1 25.9b 52.8b
m "8 tit m
m rs L m m

 

‘Cscontrol (mshaded); S1:shaded since July 27/90 (pea size); $2:shaded since Aug.21/90 (veraison)

001:0 clusters per vine; 301: 3 clusters per vine
'0'. *. ”. m 1100 significant or significant at the 5%, 1% or 0.1% level, respectively. Mean

separation within calm using the LSD test at 5%

 

 

222
on 82 vines. When the three partitioning dates were analyzed together, the dry

weight of both canes and roots was lower on shaded than on control vines, and trunk
dry weight was lower on 81 than on 82 vines (Table 9). Root dry weight and the sum
of the dry weight of roots, canes and trunk were negatively correlated with the
number of days under shading, when all the partitioned vines were included in the

analyses (data not shown).

[-9113 o -l’ hu-a =4 or sun 011‘ o _. '1 'i

Shading Eﬁ'ects

Vine shading reduced the percentage of fruitful primary shoots and the
number of clusters per vine and per primary shoot in the year following treatment
(Year 2), as evaluated at the whole vine level (Table 10). This is consistent with
previous reports of an inhibitory shading effect on inﬂorescence formation (May and
Antcliff, 1963; May, 1965). This reduction was especially pronounced following
shading since pea size (81) but was still signiﬁcant when shading was imposed post-
veraison (82). Thus, it can be inferred that inﬂorescence primordia formation was
probably not yet completed as late as veraison (August 21/90). Given the suggestion
of a relationship between shoot development and inﬂorescence ontogeny (Lavee gt
3.1., 1967), the reduced vine growth of the potted vines prior to shading in 1990
probably contributed to a delay in the completion of inﬂorescence primordia
formation, as discussed in Chapter IV. On the other hand, no signiﬁcant shading
effect on the number of clusters per fruitful primary shoot was observed, whether at

the vine (Table 10) or at the individual bud level (Tables 11 and 12). Hence, shading

 

 

 

 

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225

table 11. Simificance' of the effects of 1990 (Year 1) shading (SH), cropping
level (CROP), bud position (BP), presence of a cluster at a specific node
(PCL), and interactions, on the fruitfulness and yield components of potted
Seyval grapevines in 1991 (Year 2), evaluated on a 9g msi . Mean values for
SH, CROP, and BP levels relative to these analyses are presented in table 12.

 

No. set berries at 3 weeks PFB'

 

 

Factor or No. clusters

lnteraction per 1'" shoot fruitful cluster basal cluster
1‘w shoot

s" “C‘ m n ”

CROP * ns '* ns

up ii. iii it. ...

PCL(CROP)" ns ns ns ns

snicnw *9. *t

SH*BP

CRW*BP

$ﬂ'PCLlCROP)

BP‘PCL ( CRW )

Sii‘CRWBP

 

'the level of significance is indicated for the'main effects and interactions
present in the final model obtained from backwards elimination starting at
an overparametrized model that contained all the factors and interactions
listed. the main effects were always kept in the sucessive models,
regardless of their significance

'PFB: post full bloom

‘ns, *, **, *** Non significant or significant at the 5%, 1% or 0.1% level,

respectively.
“PCL(CROP): PCL nested within CROP

226

Table 11 (cont'd) .

 

 

 

Yield per Cluster Ht. (g) 7 No. berries at harvest Berry Ht. (9)

Factor or fruitful No.
lnteraction 1" shoot all the basal fruitful cluster basal all the basal seeds]

(9) clusters cluster 1" cluster clusters cluster berry

included shoot included

SR ns' * ns ns ** ** ns ns ns
CROP ns *** * ns *** ns * ns ns
8P tit tit it. it. 9*. it! if. it "8
PCL(CROP) ns ns ns ns ns ns ns ns ns
SHOCRW it as at
SIPBP
CRW‘BP
SH‘PCLlCRW)
BP‘PCLlCRW)
Sil‘CRWBP

 

'ns, *, **, *** Ion significant or significant at 5%,

1% or 0.1% level, respectively.

 

 

 

vi'
4.

...h

. I 1. ¢ a , s ..
. .. . a s . .. ‘l a . .. .ﬂ . a . ,
. . . . 3,. w x... .R 3'04’: .. H ...}.n .. . . .l. ......utl yr?“

 

227

Table 12. Influence of bud position and 1990 (Year 1) shading and cropping
level treatments on the fruitfulness and yield couponents of potted Seyval
grapevines in 1991 (Year 2), evaluated on a bug bg§;_.

 

No. set berries at 3 weeks PFB'

 

 

Factor Io. clusters
per 1'" fruitful cluster basal
shoot 1‘" shoot cluster
Shading': C 1.58 71 34 36
51 0.70 103 54 59
52 1.10 91 46 69
it!“ "S (9*) (*t)
C vs. shaded ***
s1 vs. 82 ns
Crop. level": 0Cl 1.37 84 38 62
3Cl 0.89 86 47 48
a "s (at) ns
Bud position: 1 0.16 28c 22c 25c
2 0.53 37c 24c 23c
3 0.59 31c 23c 25c
4 1.02 68b 36b 36b
5 2.02 119a 56a 60a
6 2.08 117a 52a 58a
aaa ... aaa aaa

 

zPFB: post full bloom

'C:control (unshaded); s1:shaded since July 27/90 (pea size); $2:shaded since

Aug.21/90 (veraison)

I‘ns, *, **, *** Ion significant or significant at the 5x, 1% or 0.1% level,
respectively. Least-squares means for leaf removal were separated at the 5%
level. Means for bud position were separated using Duncan's New Multiple
Range test at the 5% level. Brackets indicate that the factor is involved in
significant interactions; therefore no mean separation was performed.

'0Cl:0 clusters per vine; 3Cl:3 clusters per vine

Table 12 (cont'd).

228

 

 

 

Yield per Cluster Ht. (g) Mo. berries at harvest Berry Ht. (9)
Factor fruitful Mo.
1'" shoot all the basal fruitful cluster basal all the basal seeds/
(9) clusters cluster 1" cluster clusters cluster berry
included shoot included
Shading‘: C 79.9 37.3b 42.2 50 24 27 1.41 1.45 2.93
51 111.2 58.3a 67.0 71 37 42 1.47 1.47 2.94
82 104.2 52.1a 57.9 67 34 37 1.45 1.45 2.94
ns' " ns ns 0*) l“) ns ns ns
C vs. shaded '*
S1 vs. 82 ns
Crop. level': 0Cl 91.0 40.4b 48.2b 58 26 31 1.40 1.41 2.90
3Cl 98.7 54.0a 58.0a 62 34 36 1.48 1.50 2.98
ns *** * ns 0"“) ns (*) ns ns
Bud position: 1 29.9c 23.5c 27.2c 20c 16c 18c 1.32b 1.32b 2.98
2 33.8c 21.4c 22.1c 24c 15c 15c 1.27b 1.32b 2.73
3 28.8c 21.3c 24.0c 20c 15c 17c 1.29b 1.32b 2.72
4 72.7b 38.5b 42.5b 47b 25b 27b 1.46a 1.50ab 3.05
5 137.2a 65.4a 71 .0a 85a 40a 44a 1.52a 1.51a 2.95
6 134.8a 60.1a 72.3a 86a 38a 45a 1.49s 1.50ab 3.03
m an m aaa aaa aaa eaa aaa ns

 

'C:control (mshaded); s1:shaded since July 27/90 (pea size); $2:shaded since Aug.21/90 (veraison)
'0'. *. ”, m Mon significant or significant at the 5%, 1% or 0.1% level, respectively. Least-squares
means for leaf rellioval were separated at the 5% level. Means for bud position were separated using
Dmcan's Mew Multiple Range test at the 5% level. Brackets indicate that the factor is involved in
“Unificant interactions,- therefore no mean separation was performed.

'0Cl:0 clusters per vine; 3Cl:3 clusters per vine

229

might have inhibited the formation of the ﬁrst but not of subsequent inflorescences
within the bud. In Year 2, the number of berries per primary shoot at three weeks
post full bloom was higher on control (C) than on shaded vines, when evaluated on
a vine basis. This resulted from a higher number of clusters per primary shoot on C
vines, since these vines had a lower number of berries per cluster than the shaded
ones (Table 10). Due to a higher number of clusters (and conceivably of ﬂowers) on
C than on shaded vines, the competition among setting berries was probably stronger
and fruit set more affected on the former vines. Shading reduced the yield per vine
and per primary shoot in Year 2, while the berry weight and the number of seeds per
berry were not signiﬁeantly inﬂuenced (Table 10). The higher cluster weight of
shaded as compared to C vines was not sufﬁcient to compensate for the shade-

induced reduction in cluster number.

Cropping Level Eﬁ‘ects

Fruit development in Year 1 reduced the percentage of fruitful primary shoots
and the number of clusters in Year 2, whether expressed per vine, per primary shoot,
or per fniitful primary shoot (Table 10). This is consistent with previous reports of
a negative cropping effect on ﬂower-bud differentiation for next season’ 3 crop in
grapevines (Antcliff and Webster, 1955) and other woody plants (Jackson and Sweet,
1972). The vines that bore fruits in Year 1 (3C1) had, on the other hand, a higher
number of berries per cluster in Year 2 than non-bearing (0C1) vines (Table 10). As
discussed for Experiment 11 of Chapter IV, fruit set in Year 2 was probably lower on

0C1 than on 3Cl vines due to a stronger nutritional competition among developing

230

berries or to a less favorable hormone balance for fruit set on the former vines. As
in Experiment 11 of Chapter IV, the higher number of berries per cluster on 3Cl than
on DC] vines resulted in heavier clusters on the former vines, which compensated for
their lower number of clusters; hence, no signiﬁcant differences in yield between BC]

and DC] vines were found in Year 2 (Table 10).

Bud Position (BP) Meets

The position of the bud on the 6-node cane had a highly signiﬁcant effect on
all the fruitfulness responses evaluated except the number of seeds per berry (Tables
11 and 12). An increased fruitfulness from the base to the apex of the 6-node cane
was clearly evidenced, as in the experiments of Chapter IV and in previous studies
(Partridge, 1921; Buttrose, 1974; Champagnol, 1984; Huglin, 1986; Howell e1 31.,

1993).

Presence of a Cluster at an Individual Node (PCL)

As in the experiments described in Chapter IV, the presence of a cluster at
a speciﬁc node had no signiﬁcant influence on the Year 2 fruitfulness parameters of
the primary bud developing on that node (Table 11). This suggests that the cropping
effect on the fruitfulness of a given bud may derive mostly from the fruiting condition
(bearer or not) of the shoot in Year 1, rather than from the presence or absence of

a cluster at the particular node where the bud developed.

231

Conclusions

Vine shading to 24% of full sunlight after pea size had no signiﬁcant effect
on the net C02 assimilation rate (A) at BAS and MID leaf positions when all the
measurements after shading imposition were considered, but reduced A at the AP
leaf position. Differences in exposure during and after leaf development are probable
explanations for the above results. The shade-induced increase in leaf chlorophyll
content and decrease in chlorophyll a/b ratio, conceivably attenuated an inhibitory
shading effect on A. Shading did not preclude a photosynthetic enhancement in
response to the presence of fruits, although it appeared to decrease the intensity of
this effect at the BAS and, to a lesser extent, at the MID leaf positions. Alternatively,
shading prevented a dramatic decline in A at BAS leaves after harvest. This was
probably due to delayed senescence of the BAS leaves on shaded fruiting vines, to
the lack of a sharp post-harvest increase in ABA in these leaves, or both.

Shading increased the percentage of dry matter in leaves in the early fall, and
reduced the dry weight of roots and canes when all the partitioning dates were
considered. Whether applied post- pea size or post-veraison, shading reduced the
percentage of fruitful primary shoots and the number of clusters per vine and per
primary shoot in the following year, suggesting that inﬂorescence primordia formation
was not completed as late as veraison. This resulted in lower Year 2 yield on vines
shaded in the preceding season as compared to control vines, despite a larger
number of berries per cluster and heavier clusters on the former vines.

As in Experiment 11 of Chapter I, cropping had a signiﬁcant effect on dry

232

matter allocation unlike on total dry weight per vine. Shoots, roots, and leaves were
particularly affected by fruiting. Fruit development in Year 1 inhibited ﬂower—bud
differentiation for the following season’s crop. This inhibition was not signiﬁcantly
related to the presence of a cluster developing at the same node of a bud. Yield in
Year 2 was similar on vines that bore fruit in Year 1 and on non-bearing vines,
though, due to a compensatory increase in cluster weight on the former vines,
resulting from a higher number of berries per cluster. Bud position on the 6-node
cane had a highly signiﬁcant effect on all the fruitfulness responses except for the
number of seeds per berry. me observed increase in bud fruitfulness along the 6-
node cane is consistent with the widely reported raise in fruitfulness from the basal

to the middle region of grapevine canes.

literature cited

Antcliff, A.J.,and W.J. Webster. 1955. Studies on the Sultana vine. 1. Fruit bud
distribution and bud burst with reference to forecasting potential crop. Aust. J. Agric.
Res. 6:565-588.

Barden, LA. 1974. Net photosynthesis, dark respiration, speciﬁc leaf weight, and
growth of young apple trees as inﬂuenced by light regime. J. Amer. Soc. Hort. Sci.
99:547-551.

Berry, LA. 1975. Adaptation of photosynthetic processes to stress. Science 188:644-
650.

Bjérkman, 0. 1981. Responses to different quantum ﬂux densities. In: Lange, O.L.,
P.S. Nobel, C.B. Osmond, and H. Ziegler (Eds.). Encyclopedia of Plant Physiology,
New Series, Vol. 12A, Physiological Plant Ecology. I. Responses to Physical
Environment. Springer-Verlag, Berlin, pp. 57-107.

Buttrose, M.S. 1974. Climatic factors and fruitfulness in grapevines. Hort. Abstr.
44:319-326.

233

Champagnol, F. 1984. Elements de Physiologic de la Vigne et de Viticulture
Générale. Publ. F. Champagnol, Saint-Gely-du—Fesc. 351 pp.

Chaves, M.M. 1984. Photosynthesis and assimilate partitioning in fruiting and non-
fruiting grapevine shoots. In: Sybesma, C. (Ed.). Advances in Photosynthesis
Research. Proc. VIth Intnl. Congress on Photosynthesis, August 1983, Brussels,
Belgium, vol. IV, pp. 145-148.

Downton, W.J.S.,W.J.R. Grant, and B.R. Loveys. 1987. Diurnal changes in the
photosynthesis of ﬁeld-grown grapevines. New Phytol.105:71-80.

Downton, W.J.S., B.R. Loveys, and W.J.R. Grant. 1988. Stomatal closure fully
accounts for the inhibition of photosynthesis by abscisic acid. New Phytol. 108:263-
266.

Edson, C.E. 1991. Inﬂuence of Crop Level on Leaf and Whole Vine Photosynthesis
and Dry Matter Partitioning in Seyval Grapevines (Vitis sp.). PhD Diss., Michigan
State Univ., East Lansing. 169 pp.

Eibach, R. , and G. Alleweldt. 1985. Einﬂuss der Wasserversorgung auf Wachstum,
Gaswechsel und Substanzproduktion traubentragender Reben. III. Die
Substanzproduktion. Vitis 24:183-198 (English Abst.).

Flore, J.A., and A.N. Lakso. 1989. Environmental and physiological regulation of
photosynthesis in fruit crops. Hort. Rev. 11: 111-157.

Howell, G.S. 1988. Cultural manipulation of vine cold hardiness. In: Smart, R.E.,R.J.
Thornton, S.B. Rodriguez, and J.E. Young (Eds.). Proc. 2nd Intnl. Symp. Cool
Climate Vitic. Enol., Auckland, New Zealand, January 1988, pp. 98-102.

Howell, G.S., M.C. Candolﬁ-Vasconcelos, and W. Koblet. 1993. Inﬂuence of
defoliation, rootstock and training system on Pinot noir grapevines. IV . Second year
response of vine growth, yield and fruit composition. Am. J. Enol. Vitic. (in press).

Howell, G.S. , and N. Shaulis. 1980. Factors inﬂuencing within-vine variation in the
cold resistance of cane and primary bud tissues. Am. J. Enol. Vitic., 31:158-161.

Howell, G.S.,B.C. Stergios, and 8.8. Stackhouse. 1978. Interrelation of productivity
and cold hardiness of Concord grapevines. Am. J. Enol. Vitic. 29:187-191.

Huglin, P. 1986. Biologic ct Ecologie de la Vigne. Payot Lausanne, Paris. 372 pp.

Jackson, J.E., and G.B. Sweet. 1972. Flower initiation in temperate woody plants.
Hort. Abst. 42:9-24.

234

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