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THESPS

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This is to certify that the
thesis entitled

ROOTSTOCK AF FECTS FLOWER DISTRIBUTION AND
PATTERNING IN ‘HEDELFINGER' (Prunus avium L.) SWEET
CHERRY AND ‘MONTMORENCY' (P. cerasus L.) TART
CHERRY

presented by
KAREN MAGUYLO

has been accepted towards fulﬁllment
of the requirements for the

MS. degree in Horticulture

@3047 241%

Major P'rofessor’s Signatfrj

Date

 

MSU is an Afﬁrmative ActiorVEqual Opportunity Institution

 

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LIBRARY
Michigan State
University

 

 

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6/01 c/CIRC/DateDuepGS—sz

 

ROOTSTOCK AF FECTS FLOWER DISTRIBUTION AND PATTERNING IN
‘HEDELFINGER’ (Prunus avium L.) SWEET CHERRY AND ‘MONTMORENCY’ (P.
cerasus L.) TART CHERRY
By

Karen Maguylo

A THESIS
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Horticulture

2003

ABSTRACT
ROOTSTOCK AF FECTS FLOWER DISTRIBUTION AND PATTERN ING IN
‘HEDELFINGER’ (Prunus avium L.) SWEET CHERRY AND ‘MONTMORENCY’ (P.
cerasus L.) TART CHERRY
By

Karen Maguylo

New precocious and highly productive cherry rootstocks have led to management
challenges for balancing of crop levels with adequate leaf area to assure good fruit size
and quality. To examine how different cropping potentials might be managed more
strategically, the inﬂuence of individual rootstock genotypes on ﬂower bud distribution
and density was characterized using ‘Hedelﬁnger’ sweet cherry (Prunus avium L.) and
‘Montmorency’ tart cherry (Prunus cerasus L.) scions. Flower bud formation occurs
solitarily on one-year-old shoots, or on spurs of two-year and older shoot sections. In
2001 (trees planted spring 1998 as part of the NC-14O regional tree fruit rootstock
project), the second- year shoot section of branches was used to characterize rootstock
inﬂuence on the development of ﬂowers, buds, spurs, blind nodes, lateral shoots, and
ultimately crop load. Both rootstock and position within the second-year-shoot section
affected ﬂower number per bud. Rootstock genotype also inﬂuenced location of lateral
shoots, spurs, and vegetative axillary buds. These spur locational and ﬂowering
characteristics provide helpful parameters for evaluating, and eventually managing, such

rootstocks that can dramatically alter sweet and tart cherry scion precocity and/or vigor.

Copyright by
KAREN MAGUYLO
2003

ACKNOWLEDGMENTS

I am grateful for everyone that was involved in the project. I would like to especially

thank Dr. Jim Flore, Dr. Steve van Nocker, Jim Olmstead, and Costanza Zavalloni.

 

 

 

 

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TABLE OF CONTENTS

LIST OF TABLES ......................................................................................................... vii
LIST OF FIGURES ........................................................................................................ xv

CHAPTER I: Literature Review

Introduction ........................................................................................................ 2
Patterns in trees ................................................................................... 3
Flowering ............................................................................................ 7
Growth and fruiting habits of cherry trees ........................................ 18

References ........................................................................................................ 21

 

CHAPTER H: Rootstock Affects Floral Distribution and Patterning in ‘Hedelﬁnger’

Sweet Cherry

Abstract ........................................................................................................... 28
Introduction ...................................................................................................... 29
Materials and Methods ..................................................................................... 32
Plant Materials .................................................................................. 32
Data Collection ................................................................................. 32
Statistical Analysis ............................................................................ 36
Results ........................................................................................................... 36
Flower Bud Number per Spur ........................................................... 36
Flower Number per Bud ................................................................... 36
Metamer Lengths .............................................................................. 41
Distribution of Metamer Types ......................................................... 41

Trunk Cross-Sectional Area Increase and Spur Flowering
Characteristics ....................................................................... 48
Flowers per Bud Versus Buds per Spur ............................................ 51
Discussion ........................................................................................................ 51
Literature Cited ................................................................................................ 56

 

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TABLE OF CONTENTS (Continued)

CHAPTER III: Rootstock Affects Floral Distribution and Patterning in ‘Montmorency’
Tart Cherry

Abstract ........................................................................................................... 58
Introduction ...................................................................................................... 59
Materials and Methods ..................................................................................... 62
Plant Materials .................................................................................. 62
Data Collection ................................................................................. 64
Statistical Analysis ............................................................................ 66
Results ........................................................................................................... 67
Flower Bud Number per Spur ........................................................... 67
Flower Number per Bud ................................................................... 67
Metamer Lengths .............................................................................. 67
Distribution of Metamer Types ......................................................... 75
Trunk Cross-Sectional Area Increase and Spur Flowering
Characteristics ....................................................................... 75
Flowers per Bud Versus Buds per Spur ............................................ 80
Discussion ........................................................................................................ 80
Literature Cited ................................................................................................ 86
APPENDIX A: Pairwise Comparisons .......................................................................... 88
APPENDIX B: LEAF Y project .................................................................................. 137
vi

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LIST OF TABLES

CHAPTER II

Table 2-1 Rootstocks, listed in order of increasing vigor, characterized in
the 1998 NC-14O ‘Hedelﬁnger’ sweet cherry rootstock trial at the
NWI-IRS near Traverse City, Michigan. Vigor values are based
on 2001 TCSA. Genotypes are clonal selections unless
otherwise noted ..................................................................................... 33

Table 2-2 The effect of rootstock, listed in order of increasing vigor, on the
average number of ﬂowers per bud and ﬂoral buds per spur (i
standard error) on the entire two-year-old shoot section of
‘Hedelﬁnger’ sweet cherry. Counts were taken in the 2001
growing season ..................................................................................... 37

Table 2-3 The effect of rootstock, listed in order of increasing vigor, on the
average number of ﬂowers per bud and ﬂoral buds per spur (i
standard error) in the proximal part of two-year-old shoot section
of ‘Hedelﬁnger’ sweet cherry. Counts were taken in the 2001
growing season ..................................................................................... 38

Table 2-4 The effect of rootstock, listed in order of increasing vigor, on the
average number of ﬂowers per bud and ﬂoral buds per spur (1
standard error) in the medial part of two-year-old shoot section
of ‘Hedelﬁnger’ sweet cherry. Counts were taken in the 2001
growing season ..................................................................................... 39

Table 2-5 The effect of rootstock, listed in order of increasing vigor, on the
average number of ﬂowers per bud and ﬂoral buds per spur (3:
standard error) in the distal part of two-year-old shoot section of
‘Hedelﬁnger’ sweet cherry. Counts were taken in the 2001
growing season ..................................................................................... 40

Table 2-6 Analysis of variances for the number of buds per spur, ﬂowers
per bud, and metamer lengths from different rootstock treatments
and from different sections within the two-year-old shoots of
those treatments. Analyzed data were collected during the 2001
growing season. .................................................................................... 42

Table 2-7 Analysis of variances for percentages of blind nodes, single
vegetative axillary buds, lateral shoots, and spurs from different
rootstock treatments and from different sections within the two-
year-old ‘Hedelﬁnger’ shoots of those treatments. Analyzed data
were collected during the 2001 growing season ................................... 44

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Table 2-8 The effect of rootstock, listed in order of increasing vigor, on
relative amounts of different node types (blind node, single
vegetative axillary bud, lateral shoot, and spur) in the proximal
section of the two-year-old shoots of ‘Hedelﬁnger’ sweet cherry.
Shoots were analyzed as three sections (proximal, medial, and
distal) of equal length. Counts were taken in the 2001 growing
season, and are reported in each column as percentage of the
total number of nodes (i standard error). ............................................. 45

Table 2-9 The effect of rootstock, listed in order of increasing vigor, on
relative amounts of different node types (blind node, single
vegetative axillary bud, lateral shoot, and spur) in the medial
section of the two-year-old shoots of ‘Hedelﬁnger’ sweet cherry.
Shoots were analyzed as three sections (proximal, medial, and
distal) of equal length. Counts were taken in the 2001 growing
season, and are reported in each column as percentage of the
total number of nodes (i standard error). ............................................. 46

Table 2-10 The effect of rootstock, listed in order of increasing vigor, on
relative amounts of different node types (blind node, single
vegetative axillary bud, lateral shoot, and spur) in the distal
section of the two-year-old shoots of ‘Hedelﬁnger’ sweet cherry.
Shoots were analyzed as three sections (proximal, medial, and
distal) of equal length. Counts were taken in the 2001 growing
season, and are reported in each column as percentage of the
total number of nodes (i standard error). ............................................. 47

CHAPTER III

Table 3-1 Rootstocks, listed in order of increasing vigor, characterized in
the 1998 ‘Montmorency’ tart cherry trial at the NWHRS near
Traverse City, Michigan. Vigor values are based on the 2001
TCSA. Genotypes are clonal selections unless otherwise noted ......... 63

Table 3-2 : The effect of rootstock, listed in order of increasing vigor, on
the average number of ﬂowers per bud and ﬂoral buds per spur
(i standard error) on the entire two-year-old shoot section of
‘Montmorency’ tart cherry .................................................................... 68

Table 3-3 The effect of rootstock, listed in order of increasing vigor, on the
average number of ﬂowers per bud and ﬂoral buds per spur (i
standard error) in the proximal part of the two-year—old shoot
section of ‘Montmorency’ tart cherry. Counts were taken in the
2001 growing season ............................................................................ 69

viii

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Table 3-4 The effect of rootstock, listed in order of increasing vigor, on the
average number of ﬂowers per bud and ﬂoral buds per spur (i
standard error) in the medial part of the two-year-old shoot
section of ‘Montmorency’ tart cherry. Counts were taken in the
2001 growing season ............................................................................ 70

Table 3-5 The effect of rootstock, listed in order of increasing vigor, on the
average number of ﬂowers per bud and ﬂoral buds per spur (i
standard error) in the distal part of the two-year-old shoot section
of ‘Montmorency’ tart cherry. Counts were taken in the 2001
growing season ..................................................................................... 71

Table 3-6 Analysis of variances for the number of buds per spur, ﬂowers
per bud, and metamer lengths from different rootstock treatments
and from different sections within the two-year-old shoots of
those treatments. Analyzed data were collected during the 2001
growing season ..................................................................................... 74

Table 3-7 The effect of rootstock, listed in order of increasing vigor, on the
relative amounts of different node types (blind node, single
vegetative axillary bud, lateral shoot, and spur) in the distal
section of the two-year-old shoots of ‘Montmorency’ tart cherry.
Shoots were analyzed as three sections (proximal, medial, and
distal) of equal length. Counts were taken in the 2001 growing
season. Numbers reported in each column are percents of the
total number of nodes (i standard error) .............................................. 77

Table 3-8 Analysis of variances for the percentages of blind nodes, single
axillary vegetative buds, lateral shoots, and spurs from different
rootstock treatments and from different sections within the two-
year-old ‘Montmorency’ shoots of those treatments. Analyzed
data were collected during the 2001 growing season ........................... 78

Table 3-9 The effect of rootstock, listed in order of increasing vigor, on the
relative amounts of different node types (blind node, single
vegetative axillary bud, lateral shoot, and spur) in the medial
section of the two-year-old shoots of ‘Montmorency’ tart cherry.
Shoots were analyzed as three sections (proximal, medial, and
distal) of equal length. Counts were taken in the 2001 growing
season. Numbers reported in each column are percents of the
total number of nodes (i standard error) .............................................. 79

Table 3-10 The effect of rootstock, listed in order of increasing vigor, on the

relative amounts of different node types (blind node, single
vegetative axillary bud, lateral shoot, and spur) in the proximal

ix

 

section of the two-year-old shoots of ‘Montmorency’ tart cherry.

Shoots were analyzed as three sections (proximal, medial, and

distal) of equal length. Counts were taken in the 2001 growing

season. Numbers reported in each column are percents of the

total number of nodes (i standard error) .............................................. 81

APPENDIX A

Table A1 Comparison of buds per spur values in the proximal section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 89

Table A2 Comparison of buds per spur values in the medial section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 90

Table A3 Comparison of buds per spur values in the distal section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 91

Table A4 Comparison of marginal buds per spur values of ‘Hedelﬁnger’
sweet cherry two-year old shoots from 16 different rootstocks.
P-values show signiﬁcance of each interaction. ................................... 92

Table A5 Comparison of ﬂowers per bud values in the proximal section of
‘Hedelﬁnger’ sweet cherry two-year old shoots ﬁ'om 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 93

Table A6 Comparison of ﬂowers per bud values in the medial section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 94

Table A7 Comparison of ﬂowers per bud values in the distal section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 95

Table A8 Comparison of marginal ﬂowers per bud values of ‘Hedelﬁnger’
sweet cherry two-year old shoots from 16 different rootstocks.
P-values show signiﬁcance of each interaction. ................................... 96

Table A9 Comparison of internode length values in the proximal section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 97

Table A10 Comparison of internode length values in the medial section of

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‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 98

Table A1 1 Comparison of internode length values in the distal section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. ................ 99

Table A12 Comparison of marginal internode length values of ‘Hedelﬁnger’
sweet cherry two-year old shoots ﬁ'om 16 different rootstocks.
P-values show signiﬁcance of each interaction. ................................. 100

Table A13 Comparison of percentage of blind node values in the proximal
section of ‘Hedelﬁnger’ sweet cherry two-year old shoots from
16 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 101

Table A14 Comparison of percentage of blind node values in the medial
section of ‘Hedelﬁnger’ sweet cherry two-year old shoots ﬁom
16 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 102

Table A15 Comparison of percentage of blind node values in the distal
section of ‘Hedelfinger’ sweet cherry two—year old shoots from
16 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 103

Table A16 Comparison of percentage of vegetative axillary bud values in
the proximal section of ‘Hedelﬁnger’ sweet cherry two-year old
shoots from 16 different rootstocks. P-values show signiﬁcance
of each interaction ............................................................................... 104

Table A17 Comparison of percentage of vegetative axillary bud values in
the medial section of ‘Hedelﬁnger’ sweet cherry two-year old
shoots ﬁ'om 16 different rootstocks. P-values show signiﬁcance
of each interaction. .............................................................................. 105

Table A18 Comparison of percentage of vegetative axillary bud values in
the distal section of ‘Hedelﬁnger’ sweet cherry two-year old
shoots ﬁ‘orn 16 different rootstocks. P-values show signiﬁcance
of each interaction ............................................................................... 106

Table A19 Comparison of percentage of lateral shoot values in the proximal
section of ‘Hedelﬁnger’ sweet cherry two-year old shoots from
16 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 107

 

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Table A21

Table A22

Table A23

Table A24

Table A25

Table A26

Table A27

Table A28

Table A29

Table A30

Comparison of percentage of lateral shoot values in the medial

section of ‘Hedelﬁnger’ sweet cherry two-year old shoots from

16 different rootstocks. P-values show signiﬁcance of each

interaction. .......................................................................................... 108

Comparison of percentage of lateral shoot values in the distal

section of ‘Hedelﬁnger’ sweet cherry two-year old shoots from

16 different rootstocks. P-values show signiﬁcance of each

interaction. .......................................................................................... 109

Comparison of percentage of spur values in the proximal section

of ‘Hedelﬁnger’ sweet cherry two-year old shoots from 16

different rootstocks. P-values show signiﬁcance of each

interaction. .......................................................................................... 110

Comparison of percentage of spur values in the medial section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 111

Comparison of percentage of spur values in the distal section of
‘Hedelﬁnger’ sweet cherry two-year old shoots from 16 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 112

Comparison of buds per spur values in the proximal section of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 113

Comparison of buds per spur values in the medial section of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. ............. 114

Comparison of buds per spur values in the distal section of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 115

Comparison of marginal buds per spur values of ‘Montmorency’
tart cherry two-year old shoots ﬁ'om 11 different rootstocks. P-
values show signiﬁcance of each interaction. ..................................... 116

Comparison of ﬂowers per bud values in the proximal section of
‘Montmorency’ tart cherry two-year old shoots ﬁ'om 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 117

Comparison of ﬂowers per bud values in the medial section of

‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 118

xii

 

Table A31 Comparison of ﬂowers per bud values in the distal section of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 119

Table A32 Comparison of marginal ﬂowers per bud values of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 120

Table A33 Comparison of internode length values in the proximal section of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 121

Table A34 Comparison of internode length values in the medial section of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 122

Table A35 Comparison of internode length values in the distal section of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 123

Table A36 Comparison of marginal internode length values of
‘Montmorency’ tart cherry two-year old shoots from 11 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 124

Table A37 Comparison of percentage of blind node values in the proximal
section of ‘Montmorency’ tart cherry two-year old shoots from
11 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 125

Table A38 Comparison of percentage of blind node values in the medial
section of ‘Montmorency’ tart cherry two-year old shoots from
11 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 126

Table A39 Comparison of percentage of blind node values in the distal
section of ‘Montmorency’ tart cherry two-year old shoots from
11 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 127

Table A40 Comparison of percentage of axillary vegetative bud values in
the proximal section of ‘Montmorency’ tart cherry two-year old
shoots from 12 different rootstocks. P-values show signiﬁcance
of each interaction. .............................................................................. 128

Table A41 Comparison of percentage of axillary vegetative bud values in

xiii

the medial section of ‘Montmorency’ tart cherry two-year old
shoots from 12 different rootstocks. P-values show signiﬁcance
of each interaction. .............................................................................. 129

Table A42 Comparison of percentage of axillary vegetative bud values in
the distal section of ‘Montmorency’ tart cherry two-year old
shoots from 12 different rootstocks. P-values show signiﬁcance
of each interaction ............................................................................... 130

Table A43 Comparison of percentage of lateral shoot values in the proximal
section of ‘Montmorency’ tart cherry two-year old shoots ﬁom
12 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 131

Table A44 Comparison of percentage of lateral shoot values in the medial
section of ‘Montmorency’ tart cherry two-year old shoots ﬁ'om
12 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 132

Table A45 Comparison of percentage of lateral shoot values in the distal
section of ‘Montmorency’ tart cherry two-year old shoots from
12 different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 133

Table A46 Comparison of percentage of spur values in the proximal section
of ‘Montmorency’ tart cherry two-year old shoots from 12
different rootstocks. P-values show signiﬁcance of each
interaction. .......................................................................................... 134

Table A47 Comparison of percentage of spur values in the medial section of
‘Montmorency’ tart cherry two-year old shoots from 12 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 135

Table A48 Comparison of percentage of spur values in the distal section of

‘Montmorency’ tart cherry two-year old shoots from 12 different
rootstocks. P-values show signiﬁcance of each interaction. .............. 136

APPENDD( B

Table Bl Sequence of 923 bp region (see section 2-6 and 2-7) used as a
probe for the northern analysis. Sequence shows 86% identity
with Malus x domestica AF L2 mRNA.. ............................................. 149

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LIST OF FIGURES

CHAPTER H

Figure 2-1* Illustration of a two-year-old (and associated one-year-old)
cherry shoot. Red lines indicate the different sections by
which the shoot was analyzed .......................................................... 34

Figure 2-2"' Percentage of nodes within each section (proximal, medial,
distal) of a two-year-old ‘Hedelﬁnger’ sweet cherry shoot
having no buds (black), only vegetative axillary buds
(green), lateral shoots (brown), or spurs (red). Rootstocks
are listed in order of decreasing vigor. ............................................ 43

Figure 2-3 Floral bud number per spur in each section of two-year-old
‘Hedelﬁnger’ sweet cherry shoots versus 2000 TCSAI.
Bud counts were made during spring 2001. Each point
represents the average ﬂoral bud number per spur for the
speciﬁed section of a single rootstock treatment. ............................ 49

Figure 2-4 Flower number per bud of two-year-old ‘Hedelﬁnger’
sweet cherry shoots versus 2000 TCSAI. Flower counts
were made during spring 2001. Each point represents the
average ﬂower number per bud for a single rootstock
treatment. ......................................................................................... 50

Figure 2-5 Flower number per bud of each shoot section plotted
against its corresponding ﬂoral bud number per spur. Each
point represents the average number of ﬂowers per bud and
ﬂoral buds per spur in the speciﬁed section of two-year-old
‘Hedelﬁnger’ sweet cherry shoots of a single rootstock
treatment. ......................................................................................... 52

CHAPTER [E

Figure 3-1* Illustration of a two-year—old (and associated one-year-old)
cherry shoot. Red lines indicate the different sections by
which the shoot was analyzed .......................................................... 65

Figure 3-2 Floral bud number per spur in each section of two-year-old
‘Montmorency’ tart cherry shoots versus 2000 TCSAI.
Bud counts were made during spring 2001. Each point
represents the average ﬂoral bud number per spur for the
speciﬁed section of a single rootstock treatment. ............................ 72

XV

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Figure 3-3 Flower number per bud of two-year-old ‘Montmorency’
tart cherry shoots versus 2000 TCSAI. Flower counts
were made during spring 2001. Each point represents the
average ﬂower number per bud for a single rootstock
treatment. ......................................................................................... 73

Figure 3-4* Percentage of nodes within each section (proximal,
medial, distal) of a two-year-old ‘Montmorency’ tart
cherry shoot having no buds (black), only vegetative
axillary buds (green), lateral shoots (brown), or spurs
(red). Rootstocks are listed in order of decreasing vigor ................ 76

Figure 3-5 Flower number per bud of each shoot section plotted
against its corresponding ﬂoral bud number per spur.
Each point represents the average number of ﬂowers per
bud and ﬂoral buds per spur in the speciﬁed section of
two-year-old ‘Montmorency’ tart cherry shoots of a single

rootstock treatment .......................................................................... 82
APPENDIX B
Figure B1 Southern blot (see section 2-5). Arrow shows the 763 bp

fragment. ........................................................................................ 150
Figure B2 Northern Analysis (see section 2-7) of bud samples

collected during 2002 (see section 2-2). Arrow shows the
Gisela 6, August 14th 923 bp band, which was the only
one observed in the northern analysis. ........................................... 151

* Some images in this thesis are presented in color.

xvi

CHAPTER ONE

Literature Review

 

 

 

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INTRODUCTION
Cherry Production

The United States (US) produced 369.3 million pounds and 230,100 tons of
tart (Prunus cerasus L.) and sweet (P. avium L.) cherries, respectively, during 2001
(NASS, 2002). Michigan is the largest US. producer of tart cherries and one of the four
largest sweet cherry -- producing states (Westwood, 1993). ‘Montmorency’ is the main
tart variety, and ‘Hedelﬁnger’ is one of the main sweet varieties grown in Michigan.
Both varieties are also grown extensively worldwide (Westwood, 1993).

Many of the hit crops in the US are becoming less proﬁtable due, in part, to
increased labor costs and increased foreign competition. However, ﬂesh market sweet
cherries are one of the few ﬁ'uit crops in the US increasing in value (NASS, 2001). A
short postharvest life and limited climatic adaptability foster a proﬁtable niche in world
markets and reduced competition. Although cherry production has increased worldwide
due to current proﬁtability, the US has a higher labor cost than many production areas. If
production and labor costs can be reduced for sweet and tart cherries, the US has the
potential to remain among the leading world cherry exporters. Growers, then, must
explore ways to reduce input costs and increase productivity, thereby maintaining or
increasing their proﬁts. One strategy to both increase productivity and reduce input costs
is to improve and utilize knowledge of ﬂowering (and ultimately ﬁ'uiting) habits, which
can lead to the optimization of cultural practices such as tree training and pruning. This,
in turn, can increase production efﬁciency.

Flowering and fruiting habits can be explored on a variety of levels. The

whole plant as well as the individual bud is inﬂuenced by both exogenous and

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endogenous factors. These factors can contribute to location of ﬂowers and the density
of ﬂowers in a given area of the plant or shoot. This review will cover:
- Patterns in trees
The concept of pattern and different levels of patterning within trees
- Flowering
Juvenility, ﬂower initiation, and factors affecting ﬂower initiation

- The growth and ﬁ'uiting habit of cherry

PATTERNS IN TREES
The concept of pattern

The three components in the study of living systems are theorized to be: (1)
pattern, (2) structure, and (3) process (Maturana and Varela, 1987). The description of
the pattern involves an abstract mapping of relationships within an organism, whereas the
description of the structure involves describing the system’s actual physical components
(shape, chemical composition, etc.). The third component, process, is the link between
pattern and structure. It is necessary to continually maintain patterns in living organisms
and move matter and energy through the structure. In summary, patterns can be
recognized only if they are embodied in a physical structure, and in living organisms, this
embodiment is an ongoing process.

The study of trees can be divided into the study of pattern, structure, and
process as well. Godin and Caraglio (1998) have divided the study of trees into the study

of their different ‘structures’ such as spatial structure (the study of plant constituents in 3-

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dimensional space), mechanical structure (distribution of mechanical constraints),
topological structure, etc. Topological structure is the breaking down of a plant into
elementary constituents and then describing the connection between the constituents.
Topological structure, by this deﬁnition, is the same as pattern as deﬁned by Maturana

and Varela (1987).

Levels of Pattern in Trees

Flower bud “quality” is a parameter often questioned by tree fruit growers,

 

and Crabbé (1984) stated that better forecasting of ﬂower location would provide a more i
accurate base from which to study this characteristic. Commitment of a meristem to one
developmental pathway (ﬂowering) stops that meristem from following another
developmental pathway. The location of speciﬁc reproductive or vegetative meristems
has been suggested to be a more accurate predictor of resource allocation in plants than
ﬁxed carbon or nutrients, and this resource allocation inﬂuences ﬂowering and fruit
quality. So far, it is hard to predict where and when ﬂower buds are initiated. It is
suggested that the rate of node production (plastochron) is related to the resultant
meristem activity, such that shorter plastochrons result in ﬂoral meristems while longer
plastochrons result in vegetative meristems (Crabbe, 1984).

The productive potential of a tree consists of three levels of growth: (1) general
architecture, or the growth pattern of the main stem and its scaffolds, (2) type and
arrangement pattern of the spurs on the branch, and (3) natural evolution, or aging, of the
spurs (Lespinasse and Lauri, 1996). Clearly, then, pattern is a large part of the productive

potential of the tree. Practical applications of studying pattern in fruit trees include: (1)

 

 

 

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the creation of new tree types through breeding due to the selection of speciﬁc growth
and ﬂowering habits, (2) development of new training systems that will have reduced or
simpliﬁed pruning and thinning requirements, and natural regulation of fruit production,
and (3) a more rational approach to cultivation, for example, pruning that would lead to
an improvement in fruit quality characteristics and less labor costs (Lespinasse and Lami,
1996). Another useful aspect of studying patterns is that the resulting training systems
can be applied to other species with similar branch and ﬂower patterns.

The study of pattern in trees can be accomplished at many levels. Tree
architecture organizes a tree in both space and time. The two main purposes for the study
of tree architecture are: (1) plant growth modeling, and (2) analysis of architecture. The
analysis of architecture can be used as a base to study the application of architecture in
horticultural or forestry contexts. The application of architectural analyses, however,
requires the quantiﬁcation of architecture.

Hallé and Oldeman (1970) characterized the architecture of trees through the
use of the architectural model. The parameters used to separate individual species into
groups are based on patterns of meristematic development and branching behavior. The
analysis of meristem development led Hallé and Oldeman (1970) to distinguish at least
25 architectural models. These models are stable and usually constant throughout the life
of the plant. Architectural models allow the classiﬁcation of trees into one of these
models or the combination of two models via quantifying the architecture of the tree.

For a more speciﬁc analysis of pattern, a single tree can be divided into parts
either artiﬁcially or naturally. Artiﬁcial division of a tree simply means that there is no

biological reason for the division, such 10 cm of shoot length. Natural division uses

 

 

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morphological features to identify plant components, such as nodes on shoots. Plants can
be divided into components with identical nature, called modules. Modules are the
products of a single apical meristem, and so pattern is related to growth of each apical
meristem (Godin and Caraglio, 1998; White, 1984).

Growth of angiosperrn shoots can be described as a series of repeating units
(metamers) that are formed sequentially by the apical meristem. In the most basic form,
a metamer consists of a node with the associated leaf-like organ, lateral meristem in the
axil of the leaf, and the internode (White, 1984). According to this concept, much, if not
all, of the variation observed in shoot patterns can be accounted for by differences in the
number of metameric units produced per shoot, their rotational orientation with respect to
each other (phyllotaxy), and the metameric unit type (meristem fate). The developmental
signiﬁcance of the metameric unit concept in plants has not been established clearly
(Rutishauser and Sattler, 1985), but it offers a logical and easy way to describe variation
in shoot patterns (van Groenendael, 1985). Schultz and Haughn (1991) suggest that there
is an ordered array of different metamers in a mature Arabidopsis thaliana (Arabidopsis)
and that there must be mechanisms that specify the type of metamer to be produced at a
particular time in development. This suggestion can also be applied to trees.

Pattern and arrangement of ﬂowers have been noted across various fruit tree
species. Perez-Gonzalez (1993) demonstrated that, of 50 different peach (P. persica L.
Batsch) cultivars, there was a difference in ﬂower bud distribution based on origin of the
cultivar. Three broad classes were found: (1) genotypes with more than 60% of nodes
having one bud, which were from Mediterranean climates, (2) cultivars with more than

30% of nodes having three buds, originating ﬁ'orn colder climates, and (3) cultivars with

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a relatively even distribution of nodes having one, two, or three buds. The proportion of
blind nodes was correlated negatively with bud number per node in peach, and that
proportion of nodes with one bud was correlated negatively with nodes that have 2 or 3
buds. Schaumberg and Gruppe (1985) reported that the effect of rootstock on the number
of ﬂoral buds per spur was small on ‘Hedelﬁnger’ sweet cherry, but that there was a
signiﬁcant effect on the number of ﬂowers per bud. They also noticed that the number of
buds per spur was correlated strongly with the location of the spur within the branch.

The number of buds per spur increased distally along two-, three-, and four-year old
shoots. The greatest spur ﬂowering and fruiting occurred on the two-year-old shoot
sections, while ﬂowering and ﬁ'uiting of individual spurs declined with spur age
(Schaumberg and Gruppe, 1985). In a similar rootstock trial in Germany, rootstock
affected the distribution, as well as density, of spurs within the shoot (Franken-Bembenek

and Gruppe, 1985).

FLOWERING
Juvenility

The growth of ﬂowering plants is divided into two different phases. First,
there is a juvenile vegetative phase, during which leaves and lateral shoots are produced,
and a reproductive phase, during which (concomitant with leaves and lateral shoots)
ﬂowers are produced. Currently, there is no accurate way to distinguish the end of the
juvenile phase from the non-ﬂowering adult phase in trees, so the period during which

the tree has the ability to ﬂower, but is not currently ﬂowering, is called the transition

 

 

 

 

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period (Zimmerman, 197 3). The transition period is qualitatively the same as the adult
phase, but cannot be distinguished accurately from the juvenile phase in trees (Hackett,
1985). The ability to distinquish between the juvenile and transition (adult vegetative)
phases via molecular pathways may be possible.

The length of the juvenile phase is determined genetically, and once the juvenile

 

phase has ended, ﬂower initiation can occur. Many attempts have been made to shorten .'
the juvenile phase (Zimmerman, 1972), since a long juvenile phase creates problems for

both the tree fruit production industry (long time to ﬁrst crop) and breeders (long time

between breeding cycles) (Egea-Cortines and Weiss, 2001). Once a tree has reached the i

adult phase, each axillary meristem will either remain vegetative or make the transition to
produce ﬂowers (Pidkowich, 1999). Upon transition to ﬂowering, the meristem takes on
new characteristics. Most practices that result in early ﬂowering of fruit trees probably
do so by shortening the juvenile period. Treatments that speed the development of
seedling trees probably shorten the transition period. Once a tree has reached the adult
phase, it cannot make the transition back to the juvenile phase. However, cultural
practices, such as the use of vigorous rootstocks, may inﬂuence a delay in ﬂowering in
adult scions by shifting them back into the transitional period, which is still part of the

adult phase (Zimmerman, 1973).

Flower Initiation
Once the adult phase has been reached, an annual cycle of ﬂowering occurs.
The ﬂowering process is composed of three parts: (1) ﬂower initiation (or ﬂower

induction), (2) differentiation (or development) of the growing ﬂoral meristem, and (3)

bloom (Kozlowski, 1971). Flower initiation is a qualitative change in which a meristem
is programmed to form ﬂowers (Bewley et al., 2000). In trees, the partially developed
buds receive a signal for ﬂower initiation to begin, although the nature of this signal is
unknown (Faust, 1989). Flower bud differentiation is when visible morphological
changes occur at the growing point. One idea is that hormones have a large inﬂuence
over the early parts of bud development, and that carbohydrates and nitrogen availability
are more of the limiting factor in later parts of bud development (Faust, 1989). Flower
differentiation culminates in bloom (Bewley et al., 2000).

In both sweet and tart cherry trees, differentiation of the growing point has been
observed using the scanning electron microscope by Guimond et al. (1998a) and Diaz et
a1. (1981), respectively. Changes in the sweet cherry meristem are evident 91-105 days
after full bloom. Early in the visible transformation of a vegetative bud to a ﬂoral bud is
a broadening and ﬂattening of the rounded meristem. Then two to four small lateral
protuberances (primordial), representing primordial bracts, which subtend each ﬂower,
develop. Individual ﬂower primordia are then evident in the axil of each bract. Over the
summer, sepal primordia differentiate ﬁrst, then petals, stamens, and ﬁnally pistils. By

leaf fall, all the ﬂoral parts are visible in an immature stage (Thompson, 1996).

Pathway of Flower Initiation

Progress has been made in understanding the pathway of ﬂower initiation using
molecular biology (Pidkowich et al., 1999). The shoot apical meristem (SAM) of higher
plants is the site of ﬂoral initiation. The SAM consists of a small number of

undifferentiated dividing cells that are laid out in an organized manner (Evans and

Barton, 1997). In the juvenile phase, the SAM is characterized by the production of
primordia that develop into leaves, with a pattern of differentiation that is distinct ﬁom
those produced in the adult phase (Simpson et al., 1999). The importance of the
transition period to ﬂower initiation is that, normally, only the adult vegetative meristem
is competent to induce ﬂowers (Telfer and Poethig, 1998; Weigel and Nilsson, 1995).
Environmental signals that would normally induce ﬂower initiation fail to during the
juvenile phase, even though the transition period may appear phenotypically similar to
the juvenile phase (Zimmerman, 1972).

Newly discovered pathways for ﬂower initiation have shed some light on the
question of whether a plant is in the adult or juvenile phase. Up until the discoveries of
genes associated with ﬂowering, the only consistent characteristic to assess the end of the
juvenile period was the attainment and maintenance of the ability or potential to ﬂower
(Hackett, 1985). In Arabidopsis, an early-ﬂowering mutant, hasty, is the result of a faster
movement ﬁ'om the juvenile to adult vegetative phase (Telfer and Poethig, 1998). The
vegetative-to-ﬂoral transition, however, is unchanged relative to wild-type. The gene,
HASTY, promotes a juvenile pattern of vegetative development and inhibits ﬂowering by
reducing the competence of the SAM to respond to activity of the ﬂoral initiation genes
(Telfer and Poethig, 1998).

The fate of a ﬂoral meristem is highly regulated (Ma, 1998). Floral initiation is
accomplished and regulated by ﬂoral meristem identity genes (Weigel and Meyerowitz,
1993; Blazquez et al., 1997), which are also called FLIP (Floral Initiation Process) genes
(Schultz and Haughn, 1993). Floral initiation is followed by pattern formation and

organogenesis of the ﬂower, which is carried out by ﬂoral homeotic genes (Weigel and

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Meyerowitz, 1993). Floral fate of a meristem is not due to a single switch, but is a
condition that is acquired progressively. Interactions between at least ﬁve FLIP genes
have been found to determine meristem fate in Arabidopsis. These genes include
LEAFY (LFY), APETALAl (APl), CAULIFLOWER (CAL), APETALA2 (AP2), and
UNUSUAL FLORAL ORGAN S (UFO) (Pidkowich et al., 1999). Multiple pathways
that regulate the timing of the ﬂoral transition act directly or indirectly on the FLIP genes, T
which are responsible for switching the fate of the meristem from vegetative to ﬂoral

(Blazquez et al., 1997). Constitutive expression of some of these regulatory genes

 

promotes precocious ﬂowering (Ma, 1998).

All or some of these genes have been found to be well-conserved in species as
diverse as Pinus radiata (Mellerowicz et al., 1998), Populus trichocarpa (Rottrnan et al.,
2000), and Eucalyptus globulus (Southerton et al., 1998). The requirement for LFY to
make the transition is well documented (Schultz and Haughn, 1991; Huala and Sussex,
1992; Shannon and Meeks-Wagner, 1991). Although experiments have shown that LFY
is sufﬁcient to determine ﬂoral fate in Arabidopsis, it also has been suggested that
interactions between other genes are required (Liljegren et al., 1999). Evidence suggests
that LFY, APl, and AP2 gene products all have a role in switching meristems from a
vegetative fate to a ﬂoral fate by suppressing the vegetative pathway and activating ﬂoral
pathway. It has been shown that APl and LFY act together to specify ﬂoral meristem
fate, even though constitutive expression of LF Y alone can determine ﬂoral meristem
fate, and cause precocious ﬂowering in Arabidopsis. In an experiment by Weigel and
Nilsson (1995), in which LFY was constitutively expressed via the 35-S promoter, both

aspen (Populus spp.) and Arabidopsis formed solitary ﬂowers instead of shoots in the

11

axils of vegetative leaves. API has been demonstrated to positively regulate LF Y, and in
turn, LFY can positively regulate APl . They appear to work together to specify the ﬂoral
meristem fate (Lilj egren et al., 1999). Early expression of AP] has been found to be the
result of transcriptional activation by LFY, and was independent of protein synthesis
(Wagner et al., 1999). It has been shown that TFL (TERMINAL FLOWERl) is a
negative regulator of both LFY and API in Arabidopsis (Liljegrin et al., 1999; Mandel I

and Yanofsky, 1995). Because constitutive expression of LF Y results in a phenotype in

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Arabidopsis that is similar to mutations in TFL, and TFL is a spatial regulator of LF Y, it

has been suggested that LFY and TF L are antagonists (Shannon and Meeks-Wagner,

 

1991; Alvarez et al., 1992). UFO, another FLIP gene, requires LFY activity for its
function, but not its expression, so UFO could lie downstream of LFY and only control a
part of LFY ftmction (Pidkowich et al., 1999). UFO appears to play a role in ﬂoral
meristem identity, although it is known better for its function in deﬁning the boundaries
between ﬂoral organs in adjacent whorls of the ﬂower as well as between ﬂoral organs of
the same whorl (Levin and Meyerowitz, 1995). CAL is partially redundant with APl.
cal mutants have no signiﬁcant phenotype alone, but cal mutations greatly enhance apl
mutants, such that the resulting inﬂorescences of cal/apl double mutants look like
miniature cauliﬂowers, because there is a massive proliferation of ﬂoral meristematic
tissue (Bowman et al., 1993).

Ectopic expression of LF Y or APl only is not sufﬁcient to direct ﬂoral
development immediately after germination. A period of vegetative growth still occurs.
As in wild-type plants, the duration of this vegetative grth is sensitive to

environmental conditions such as photoperiod (Coupland, 1995). The connection

12

 

 

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between the ﬂowering time genes and LFY has been addressed directly (Blazquez et al.,
1998; Nilsson et al., 1998). Indeed, the ﬂowering time genes CO, GI, FCA, FVE, GA],
and GAI all play a role in activation of LFY and are required to some extent for the ﬁrll

expression of LFY function.

Factors that Influence Flower Initiation

Flower bud initiation is genetically, as well as biochemically, multifactorial,
meaning that there are many genetic and biochemical factors that directly or indirectly
affect ﬂower initiation (Bewley et al., 2000). In reviews of the subject by Zimmerman
(1972), Ryugo (1986), Buban and Faust (1982), Kozlowski (1971), Hackett (1985), Gur
(1985), and Bemier (1988), the common factors included length of the juvenile period
(and therefore, age of the tree), environmental considerations such as light and
temperature, internal processes such as growth regulators and carbohydrate supply, and

cultural practices.

Environmental Factors

Temperature has been shown to affect ﬂower bud initiation in apricot
‘Moorcot’ (Prunus armeniaca L.). High temperatures in winter increased the number of
‘Moorcot’ ﬂower buds per tree by increasing the number of ﬂower buds per node
(Jackson, 1970). It has also been demonstrated that leaf emergence and development are
dependant upon temperature and are directly related to degree-day accumulations in tart
cherry (Eisensmith et al., 1980). This is signiﬁcant since a minimum leaf area is required

for ﬂower bud initiation.

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Light is a major factor in initiation of ﬂower buds. Research has shown that
under artiﬁcial conditions (shade houses) ‘Montmorency’ tart cherry will not ﬂower
below a light level of 21% full sun, and at 36% full sun, ﬂower number per tree is greatly
reduced, although ﬂower number per bud is not different than 100% full sun conditions
(Flore, 1980). Under ﬁeld conditions, there was a signiﬁcant decrease in ﬂowering at

light levels below 20% full sun (Flore, 1980). Lower light levels have also been known

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to decrease leaf dry weight, total leaf dry weight per spur, and speciﬁc leaf weight in
‘Delicious’ apple (Malus domestica) (Barritt et al., 1987). Although this is not a direct

effect on ﬂowering, exposure of spur leaves to light impacts ﬂowering in the following

 

season since a minimum spur leaf area is necessary for ﬂower bud formation (Harley et
al., 1942). In apricot trees, shading results in a very pronounced decrease in ﬂower bud
initiation (Jackson, 1970). The impact of light levels on ﬂower bud initiation, then,
inﬂuences placement of ﬂower buds within the canopy of larger trees where within
canopy shading is present at levels that inhibit ﬂower bud initiation. In apple, spur leaf
area and spur leaf size were positively related to long-term productivity of the spur (Rom
and Ferree, 1984). It has been suggested that the greater yield efﬁciency of apple trees on
a more dwarﬁng rootstock, M.9, relative to more vigorous rootstocks, was due to
improved light distribution in the canopies of smaller trees (Schecter et al., 1991;
Heinicke, 1964). This increase in yield efﬁciency is most likely due to an increase in
ﬁ'uit number, the result of an increase in ﬂower initiation, since variation in ﬁ'uit number
rather then fruit weight account for most of the variation in yield in fruit trees

(Browning, 1985).

14

Plant Hormones

Since ﬂower initiation is multifactorial, the inﬂuence of a speciﬁc hormone
on ﬂower initiation is dependant on such things as time of the season, levels of other
hormones, and availability of nutrients (Faust, 1989). Although many hormones and
other molecules have been found to promote ﬂower initiation, none have been found to
be completely responsible for the control of this process (Bewley et al., 2000). It has
been hypothesized that a universal ﬂowering hormone, ﬂorigen, exists, although isolation
and characterization of the hormone has been unsuccessful (Taiz and Zeiger, 1998). The
ﬂoral initiation stimulus may involve the interaction of the hormones cytokinins and
gibberellins (GAS) (Bemier, 1988). In ﬁ'uit trees, GAs have been found to inhibit ﬂoral
initiation (Westwood, 1993), while in conifers GAs promote ﬂowering (Ekberg and
Eriksson, 1985). High endogenous levels of GAs in angiosperrns appear to be associated
with the vegetative or juvenile condition (Hackett, 1985). Cytokinins have been
implicated in cell division and enlargement, and in overcoming apical dominance by
promoting growth of inactive lateral buds (Kozlowski and Pallardy, 1997). The
interaction of cytokinins and gibberellins may be more important in ﬂoral initiation than
the action of either hormone alone (Taiz and Zeiger, 1998). Another hormone implicated
in ﬂower initiation is ethylene. In pineapple (Ananas comosus), ethephon, an ethylene-
releasing agent, increased ﬂower initiation when an adequate amount of the ethephon was
taken up by the plant (Tumbull et al., 1999).

The application of gibberellic acid (GA) accelerates precocious ﬂowering of

Arabidopsis (Langridge, 195 7). GAs accelerate primordiurn initiation at the apex, and

15

therefore, early manifestation of ﬂower induction (Evans and Blundell, 1996). The role of
GAs in activation of the LFY promoter has recently been analyzed (Blazquez et al.,

1998). The level of LF Y promoter activity is lower in GA-deﬁcient, gal, mutants.
Therefore, GAs promote ﬂowering in Arabidopsis at least in part by activating LFY

expression (Blazquez et al., 1998).

Cultural Practices:

The time of ﬂoral initiation and the number and location of ﬂower buds
initiated are inﬂuenced by certain orchard management practices (Thompson, 1996).
Since ﬂowers tend to set when growth ceases, cultural practices that decrease vigorous
shoot growth also enhance ﬂoral bud initiation (F orshey and Elving, 1989). Summer
pruning was shown to encourage ﬂower bud formation, while pruning during the dormant
period encourages more vigorous growth and so reduces ﬂower bud formation. If
summer pruning is done before growth ceases, there is generally an early vigorous
growth of new shoots. Pruning during early summer results in a delay of the maturation
of seasonal tree growth, including ﬁ'uit ripening (Chandler, 1923). Rootstocks, apart
from their inﬂuence on vigor, can inﬂuence both precocity and the amount of ﬂowering
in consecutive years (Thompson, 1996). With very dwarﬁng cherry rootstocks, early
senescence was observed in shoots and spurs of branches four years and older. Removal
of 60 — 70% of the canopy in August rejuvenated shoot growth (Schaumberg and Gruppe,

1985).

16

Rootstocks:

Rootstock use in commercial ﬁ'uit production is common due to their beneﬁcial
effects on the growth and development of the scion. In tree fruits, rootstocks are known
to affect tree size, precocity, ﬂowering, yield efﬁciency, dry matter partitioning, and hit
quality (Autio et al., 1996; Anthony et al., 1938; Warrington et al., 1990; Westwood et
al., 1976; Yadava and Doud, 1989). The tendency for trees on dwarﬁng rootstocks to
produce more ﬁ'uit relative to tree size has been well established (Hirst and F erree, 1996).
There is evidence, however, that tree size, as affected by rootstock, is not strongly related
to spur density (number of spurs per unit shoot length) or ﬂower density (number of
ﬂowers per unit shoot length) in ‘Delicious’ apple (Hirst and Ferree, 1996) or to yield in
‘Montmorency’ tart cherry (Westwood et al., 1976). In an experiment with ‘Delicious’
apple on nine rootstocks, there was a strong correlation between the number of spurs per
limb circumference and limb yield efﬁciency (g ﬁ'uit per cm limb circumference)
(Schecter et al., 1991). Schecter et a1. suggested that yield potential is inﬂuenced by
rootstock, in part, by altering the spur density of the scion. In a study by Hirst and Ferree
(1996), only half the variation observed in ﬂower density could be explained by trunk
cross-sectional area (TCSA) or shoot length, implying that rootstock has an effect on
ﬂowering independent of its affect on tree size. In this same study, rootstock effect on
ﬂower density was unrelated to its affect on spur density, so rootstocks did not inﬂuence
ﬂowering by producing a higher number of spurs. The number of leaves per spur, leaf
area per spur, and leaf area per leaf of ‘Delicious’ apple were lowest on the dwarﬁng

rootstocks, while speciﬁc leaf weight was higher. This means that the most dwarﬁng

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rootstocks inﬂuenced both shoot grth as well as vigor of individual spurs, in terms of
leaf area (Warrington et al., 1990).

Rootstock trials in Germany and the US. show an effect of rootstock on
ﬂowering in both sweet and tart cherry. Gruppe (1985a) noticed that rootstocks with at
least one tetraploid species (P. cerasus and P. fruticosa) as a parent induced signiﬁcant
precocity on the scion. It is also interesting to note that the amount of dwarﬁng had no
effect on precocity (Gruppe, 1985b). ‘Montmorency’ tart cherry on the precocious
Gisela rootstocks produced a lot of blind wood, the result of a high percentage of
ﬂowering in one-year-old laterals (Perry, 1996). Sweet cherry trees on dwarﬁng
rootstocks have an early senescence of the spurs, as well as decreasing amounts of

vegetative growth each year (Gruppe, 1985a).

GROWTH AND FRUITING HABITS OF CHERRY TREES

Sweet and tart cherries produce simple buds, which contain either leaves or
ﬂowers. Floral buds are borne either in a lateral (axillary) position on one—year old
shoots, or on spurs (shoots less than 4 cm) on two-year and older wood (Flore et al.,
1996; Thompson, 1996). In sweet cherry, the most generative spurs are located on the
two- and three-year old wood, so this is where the majority of ﬂowers occur
(W ustenberghs and Keulemans, 2000). Spurs differ between the tart and sweet cherries
in general. In sweet cherries, spurs can remain active for up to 10 years, as long as
sufﬁcient environmental requirements are met, therefore can providing a sustainable form
of ﬂowering and ﬁ'uiting. In tart cherry, spurs are most likely to be solely on the two- and

three- year—old shoots, with only a few persistant spurs in four- and ﬁve- year old shoots

18

(Thompson, 1996). In tart cherry, a greater percentage of ﬂowers are borne on axillary
buds than on spurs. This is in contrast to sweet cherries, where most of the ﬂowers are
borne on spur buds. In sweet cherries, each ﬂoral bud is surrounded by several bud
scales, and contains two to four ﬂowers; from one to six or more buds may occur on each
spur (Thompson, 1996). In tart cherries, there are also two to four ﬂowers per bud. The
percent of ﬂowers borne on one—year-old laterals relative to spurs varies between
cultivars, as well as within a cultivar, depending on cultural management. Thompson
(1996) reported that 68% of ‘Montmorency’ ﬂowers are on one-year-old shoots, whereas
another study (not cited in Thompson, 1996) showed ‘Montmorency’ bore only 35-45%
of its ﬂowers on the one-year-old laterals.

Sweet cherry trees are characterized by their strong apical dominance. This
apical dominance causes strong growth of terminal shoots and an inhibition of bud-break
for long distances below the growing point. The tart cherry has less apical dominance
and a greater tendency for production of blind wood (see below) and poor branch angles.
lateral shoots just below the leader of tart cherry trees have a tendency to become
dominant over the leader (Flore et al., 1996)

Ifthe axillary bud on a one-year-old shoot ﬂowers, in the following year the node
will be blind because it cannot initiate vegetative growth (Flore etal., 1996 ).
Production of blind nodes is cultivar dependent (Wustenberghs and Keulemans, 2000),
and decreases the productive area of the shoot. Because tart cherries have a signiﬁcant
percentage of ﬂowers borne on axillary buds (e. g. ‘Montmorency’ produces only about
30 % of its ﬂowers on spurs), there can be a large amount of blind nodes produced (Flore

et al., 1996). Blind nodes can also be the result of buds that were vegetative in the ﬁrst

19

year and inactive in the second, or spurs that did not have vegetative buds and were thus
rendered inactive in the following season (Wustenburghs and Keulemans, 2000). The
latter production of blind nodes occurs because cherries initiate ﬂowers only in buds that
have attendant leaves opening early in the summer. If the leaves are not present, then the

buds become inactive (W estwood, 1993).

20

 

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26

 

CHAPTER TWO
Rootstock Affects Floral Distribution and Patterning in ‘Hedelﬁnger’

Sweet Cherry

27

Rootstock Affects Floral Distribution and Patterning in ‘Hedelﬁnger’ Sweet

Cherry.

ABSTRACT

The NC-140 regional tree fruit rootstock project established a trial of cherry
rootstocks across North America in 1998 to evaluate their performance with the sweet
cherry scions ‘Bing’ and ‘Hedelﬁnger’. One ‘Hedelﬁnger’ trial was established near
Traverse City, Michigan. This plot was used to characterize rootstock inﬂuence on the
development of ﬂowers, buds, spurs, blind nodes, lateral shoots, and ultimately crop load,
on two-year-old shoots. Both rootstock genotype and node location on the shoot
inﬂuenced bud number per spur and ﬂower number per bud. Both bud number per spur
and ﬂowers per bud increased, in general, as tree vigor decreased. The exception was in
the Gisela/Giessen series of rootstock, in which both bud number per spur and ﬂower
number per bud decreased with a decrease in tree vigor. Both parameters increased
distally along the shoot. Rootstock genotype inﬂuenced location of lateral shoots, spurs,
vegetative axillary buds, and blind nodes on two-year old shoots. Spurs dominated in the
medial section, and lateral shoots in the distal section, of the less vigorous rootstocks,
while vegetative axillary buds dominated in all sections of the more vigorous rootstocks.
These spur locational and ﬂowering characteristics provide helpful parameters for
evaluating, and ultimately managing, such rootstocks that can dramatically alter sweet

cherry scion precocity and/or vigor.

28

INTRODUCTION

Cherry rootstocks have been selected for various reasons, including precocity,
productivity, vigor control, disease tolerance, and adaptability to different soils. With
some of these rootstocks, there is a potential problem of excessive cropping levels when
gaﬁed to very productive scion cultivars. Excessive cropping can result in poor ﬁ'uit
quality and stunted vegetative gowth (Lang, 2000). One approach to study this
phenomenon, and potentially develop strategies to manage it, is to more precisely
characterize how rootstock genotype inﬂuences tree architecture and ﬂower placement on
the scion; that is, how the development of nodes is affected differentially within a shoot
by different rootstocks. Determining gowth and location patterns of different nodes can
be used to assess how nodes are affected differentially within a shoot.

Pattemucan be studied within a tree by dividing the tree either artiﬁcially, e.g.,
empirically dividing a shoot into equal units of length, or naturally, e.g., using biological
gowth parameters that are repeated throughout the tree or have an identical nature
(Godin and Caraglio, 1998; White, 1984). Growth of angiosperrn shoots can be
described as a series of repeating units (metamers) that are formed sequentially by the
apical meristem. In the most basic form, a metamer consists of a node with an associated
leaf-like organ, a lateral meristem in the axil of the leaf, and the proximally located
internode (White, 1984). It has been suggested that there is an ordered pattern of
different metamers (Schultz and Haughn, 1991).

Distribution of different metamers within the plant plays a large part in the
productive potential of tree fruit species (Lespinasse and Lauri, 1996). Metamer types in

sweet cherry include blind nodes, lateral shoots, single vegetative buds, and spurs.

29

 

Lespinasse and Lauri suggested that studying the patterns and distribution of different
metamer types in ﬁ'uit trees would result in several practical applications including the
development of new tree gowth habits through breeding, new training systems that
reduce pruning and thinning, and a more rational approach to cultivation that could lead
to an improvement in hit quality characteristics. A better ability to predict ﬂower
location would also provide a more deﬁnitive base for the study of ﬂower bud ‘quality’
(Crabbé, 1984).

Rootstocks are known to affect spur characteristics. Franken-Bembenek and
Gruppe (1985) found that yield potential in sweet cherry was mainly dependent on
rootstock. One of the main ways the rootstock altered yield potential was by altering
location of spur insertions. Schaumberg and Gruppe (1985) tested ‘Hedelﬁnger’ sweet
cherry on some of the Giessen series rootstocks, and observed that the number of buds
per spur was not altered, but that the number of ﬂowers per bud was geatly affected by
rootstock. The number of ﬂoral buds per spur depended geatly on the position of the
spurs within the shoot. More distally located spurs produced a geater number of buds
per spur. Other correlations have been made between location of the spur and the number
of ﬂoral buds per spur in sweet cherry cultivars, indicating that position within the shoot
affects spur ﬂowering characteristics (Wustenberghs and Keulemans, 2000).

The limitation of the above trials is that they were done on a limited number
of rootstocks, and some rootstocks not in the trial may be more ideal for conditions in
Michigan. A regional tree ﬁ'uit rootstock (N C-140) trial has been established in the US to
evaluate rootstocks for suitability in the US. Rootstock can sigriﬁcantly inﬂuence ﬂower

density, as well as vigor and yield efﬁciency. Vigor and yield efﬁciency are not enough,

30

however, to predict where the ﬂowers will be borne within the canopy, which is
important for predicting and managing the productive potential of the tree.

Sweet chenies initiate ﬂowers in the summer before ﬂowering occurs, after
active gowth has ceased (Guimond et al., 1998). Spurs are ﬁrst produced in the two-
year-old shoot sections in sweet cherry. Flowering and ﬁ'uiting of individual spurs
declines with spur age, therefore the two-year old shoot section is a good predictor of the
predominant distribution of spur ﬂowering and different metamer types.

The geatest spur ﬂowering in ‘Hedelﬁnger’ sweet cherry occurs in the two-
year old shoot section. Schaumberg and Gruppe (1985) reported that the effect of
rootstock on the number of ﬂoral buds per spur was small on ‘Hedelﬁnger’ sweet cherry,
but that there was a sigriﬁcant effect on the number of ﬂowers per bud. They also
noticed that the number of buds per spur was correlated strongly with the location of the
spur within the branch. The number of buds per spur increased distally along two-, three-
, and four- year old shoots.

Schaumberg and Gruppe’s (1985) trials were in Germany, and so may not have
accurately assessed rootstocks examined in trials in the US. The objectives for this
experiment were (1) to assess the effect of rootstock and node location within two-year-
old wood on spur ﬂowering characteristics (ﬂower number per bud and bud number per
spur) and (2) to assess the effect of rootstock on location of the different metamer types
(blind nodes, single vegetative buds, lateral shoots, and spurs) in ‘Hedelﬁnger’ sweet

cherry in Michigan.

31

 

MATERIALS AND METHODS

Plant Materials

As part of the NC-140 regional tree ﬁ'uit rootstock project, a plot of ‘Hedelﬁnger’
sweet cherry (Prunus avium L.) trees on 21 rootstocks was established in spring 1998 at
Michigan State University’s Northwest Horticultural Research Station near Traverse
City, Michigan. The trees were planted in an Emmet-Leelenau sandy loam in a
randomized complete block desigr with 8 replications; however, a completely
randomized design was used for this study since the 5 most uniform replications of 16
selected rootstocks (Table 2-1) were used. The trees were trained to a modiﬁed central
leader and drip irrigated. Fertilization and protective sprays were applied as by local
standard recommendations.

Five trees per rootstock were selected for uniformity in early spring 2001.
Three shoots of comparable size and including second-year wood were randomly selected
ﬁ'om each tree’s central leader. Markings were made using paint so that the second-year
section of each shoot was divided empirically into three equal sections (proximal, medial,
and distal) (Figure 2-1).
Data Collection

In 2001, data for each node along the two-year-old section of each tagged
shoot were collected throughout the season. Each node was characterized according to its

placement within the shoot section and its type. Node types used for this study were: (1)

32

 

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34

vegetative (“axillary”) bud; (2) spur; (3) lateral (axillary) shoot (“lateral”); and (4) blind
node.

Three spur parameters were measured. Bud number in each spur was counted in
April 2001 and the number of ﬂoral buds was determined by subtracting one (for the
vegetative bud) from the total buds within the spur. Flowers within each spur were
counted on 3 May 2001. Flower number per bud was estimated by dividing the ﬂower
number per spur by the ﬂoral bud number per spur. i

The only parameters measured on nodes with lateral shoots were length of

gowth that occurred during 2000, and length of gowth that occurred during 2001 (made

 

in November 2001, after active gowth had ceased and the leaves had dropped). Metamer
lengths were estimated for each section (proximal, medial, distal). Since shoots were
split into three equal sections, the estimate was done using the following equation:

total section length
number of nodes within the section

 

Metamer length (section) a

Blind nodes were considered to be those that did not exhibit any active gowth,
whether vegetative or reproductive. Although there are different reasons for blind node
development (Wustenberghs and Keulemans, 2001), these were not ascertained in this
study. Most blind nodes of sweet cherry are due to the formation of solitary ﬂower buds
at the base of one-year-old shoots; blind nodes in this study are most likely due to such
ﬂowering during 2000.

Trunk cross-sectional area (TCSA) is an indicator of tree size (Westwood and
Roberts, 1970). Trunk cross-sectional area increase (TCSAI), then, indicates vigor of the
scion. TCSAI measurements used in this study were taken as part of the NC-l4O regional

tree research project (Cowgill and Clements, 2002).

35

vegetative (“axillary”) bud; (2) spur; (3) lateral (axillary) shoot (“lateral”); and (4) blind
node.

Three spur parameters were measured. Bud number in each spur was counted in
April 2001 and the number of ﬂoral buds was determined by subtracting one (for the
vegetative bud) from the total buds within the spur. Flowers within each spur were

counted on 3 May 2001. Flower number per bud was estimated by dividing the ﬂower

I I'—

number per spur by the ﬂoral bud number per spur.
The only parameters measured on nodes with lateral shoots were length of

gowth that occurred during 2000, and length of gowth that occurred during 2001 (made

-“—__.-_-.- .. —m , .

in November 2001, after active gowth had ceased and the leaves had dropped). Metamer
lengths were estimated for each section (proximal, medial, distal). Since shoots were

split into three equal sections, the estimate was done using the following equation:

total section length
number of nodes within th e section

 

Metamer length (section) a

Blind nodes were considered to be those that did not exhibit any active gowth,
whether vegetative or reproductive. Although there are different reasons for blind node
development (Wustenberghs and Keulemans, 2001), these were not ascertained in this
study. Most blind nodes of sweet cherry are due to the formation of solitary ﬂower buds
at the base of one-year-old shoots; blind nodes in this study are most likely due to such
ﬂowering during 2000.

Trunk cross-sectional area (TCSA) is an indicator of tree size (Westwood and
Roberts, 1970). Trunk cross-sectional area increase (TCSAI), then, indicates vigor of the
scion. TCSAI measurements used in this study were taken as part of the NC-140 regional

tree research project (Cowgill and Clements, 2002).

36

Statistical Analysis

Statistical analyses were performed using the SAS proc ghn progam (SAS
Institute, 1989). In all studies, pairwise comparisons and the analysis of variance were
used in the comparisons among rootstocks. When comparing effects of rootstock on

metamer location and ﬂowering characteristics, all values were expressed as mean i

1'“

standard error. Statistical sigriﬁcance was calculated using Student’s t-test. For the

regession analyses, highest R2 was used to determine the best ﬁtting regession curve.

w-—- t 1.: .1

RESULTS

Flower Bud Number per Spur

In general, the more vigorous rootstocks had fewer buds per spur (Table 2-2).
Trees more vigorous than those on W. 10 had no ﬂowering spurs in the proximal section
(Table 2-3) and very few ﬂowering spurs, if any, in the medial section (Table 2-4). Spur
location within the shoot section also affected ﬂower bud number per spur. The distal
section had sigriﬁcantly more buds per spur than the proximal section for all rootstocks
(Table 2-5).
Flower Number per Bud

The number of ﬂowers per bud followed the same trends as the number of buds
per spur. Rootstock affected ﬂower number per bud, with the more vigorous rootstocks
having fewer ﬂowers per bud (Table 2-2). No spurs were present in the two-year-old
shoot section of trees more vigorous than those on W. 10. There was a difference in the

number of ﬂowers per bud between the proximal and distal sections for all rootstocks

37

Table 2-3. The effect of rootstock, listed in order of increasing vigor, on
the overall number of ﬂowers per bud and floral buds per spur (:1:
standard error) in the proximal part of two-year-old shoot section of
‘Hedelfinger’ sweet cherry. Counts were taken in the 2001 growing
season.

Buds per spur Flowers per bud

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Gi. 209/1 0.9 :t 0.5 1.2 :I: 0.7
Edabriz 0.0 :I: 0.0 0.0 i 0.0
W. 53 0.8 :t 0.4 1.6 :I: 0.6
W. 72 0.6 :I: 0.2 1.7 :I: 0.7
Ci. 5 1.7 :I: 0.3 2.9 :I: 0.4
Ci. 7 2.2 :I: 0.6 2.4 :I: 0.7
Ci. 195/20 3.2 :I: 0.3 3.3 :I: 0.1
Ci. 6 1.8 :I: 0.6 2.6 :h 0.9
W. 158 0.1 :I: 0.1 0.4 :1: 0.4
W. 10 0.3 :I: 0.2 0.8 :t 0.6
W. 13 0.0 :I: 0.0 0.0 d: 0.0
Mazzard 0.0 :I: 0.0 0.0 i 0.0
Mahaleb 0.0 :I: 0.0 0.0 a: 0.0
MM 2 0.0 :I: 0.0 0.0 :I: 0.0
MM 60 0.0 :I: 0.0 0.0 :t 0.0

 

 

38

Table 2-4. The effect of rootstock, listed in order of increasing vigor, on
the overall number of ﬂowers per bud and ﬂoral buds per spur (:1:
standard error) in the medial part of two-year-old shoot section of
‘Hedelfinger’ sweet cherry. Counts were taken in the 2001 growing

season.

Gi. 209/1
Edabriz
W. 53
W. 72
Ci. 5

Ci. 7

Ci. 195/20
Ci. 6

W. 158
W. 10
W. 13
Mazzard
Mahaleb
MxM 2
MM 60

Buds per spur Flowers per bud

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

32:14 25:05
L7:11 32:02
22:12 32:02
L8:12 22:02
30:13 35:02
39:16 35:02
15:12 32:02
28:14 35:02
L5:12 30:02
L6:15 22:06
14:13 09:06
11:11 02:02
13:12 02:05
10:10 00:00
11:11 02:02

 

39

 

Table 2-5. The effect of rootstock, listed in order of increasing vigor, on
the overall number of ﬂowers per bud and ﬂoral buds per spur (:1:
standard error) in the distal part of two-year-old shoot section of
‘Hedelfinger’ sweet cherry. Counts were taken in the 2001 growing
season.

Buds per spur Flowers per bud

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

G1. 209/1 4.1 : 0.5 2.6 : 0.4
Edabriz 3.5 :I: 0.2 3.6 t 0.3
W. 53 4.0 :I: 0.3 3.1 :I: 0.2
W. 72 4.1 :I: 0.3 2.7 : 0.2
Ci. 5 4.1 :I: 0.5 3.1 d: 0.2
Ci. 7 5.1 : 0.3 3.3 :I: 0.2
Ci. 195/20 5.1 i 0.2 3.2 : 0.2
Ci. 6 4.2 : 0.3 3.2 :I: 0.2
W. 158 3.2 :I: 0.5 3.1 : 0.1
W. 10 3.4 : 0.6 2.4 : 0.3
W. 13 1.7 i: 0.3 2.6 :I: 0.4
Mazzard 0.4 : 0.2 0.8 :L- 0.4
Mahaleb 1.9 :I: 0.3 2.0 : 0.2
MxM 2 1.3 :I: 0.8 1.5 :I: 0.4
MxM 60 0.7 :I: 0.4 0.9 :I: 0.5

 

40

 

(Tables 2-3, 2-5). Proximal sections had fewer ﬂowers per bud than distal sections, and

medial sections (Table 2-4) were intermediate between the proximal and distal sections.
Metamer Lengths

Metamer lengths did not differ sigriﬁcantly between rootstocks, but did by
location within the shoot (Table 2-6). Average metamer lengths were: 4.44 i 0.11 for
the proximal, 2.62 i 0.04 for the medial, and 2.13 i 0.03 for the distal sections. Proximal
section metamer lengths ranged from 3.8 cm (Gi. 209/ 1) to 5.0 cm (Mahaleb). Distal
section metamer lengths ranged from 2.0 cm (Gi. 209/ 1) to 2.4 cm (Gi. 7). Medial
metamer lengths ranged ﬁ'om 2.4 cm (CT500) to 3.0 cm (Gi. 7). All proximal section

metamer lengths were sigriﬁcantly different from those of the distal section.
Distribution of Metamer Types

The distributions of four different metamer types (blind node, vegetative axillary
bud, lateral shoot, and spurs) were analyzed as a percentage of the total metamer number
within each section (proximal, medial, and distal) (Figure 2-2). For all four types, there
were sigriﬁcant differences both among rootstocks as well as among shoot sections
(Table 2-7). The proximal section (Table 2-8) had a relatively large amount of blind
nodes, ranging from 12 % (MxM 60) to 72 % (Gi. 209/ 1). A large number of vegetative
buds also occurred in the proximal section; however, no lateral shoots occurred in this
area. Laterals were mostly in the distal section (Table 2-10). In fact, most of the
metamers in the distal section were either lateral shoots or spurs, particularly in the less
vigorous rootstocks. In the more vigorous rootstocks, with few spurs and lateral shoots,
the single vegetative axillary buds were the most common metamer type. Relatively few

blind nodes occurred in the distal section. A broader distribution of metamer types was

41

Table 2-6. Analysis of variances for the number of buds per spur,
ﬂowers per bud, and metamer lengths from different rootstock
treatments and from different sections within the two-year-old shoots of
those treatments. Analyzed data were collected during the 2001
growing season.

 

 

 

 

 

 

 

 

Buds per spur
Source df F P>F
TRT 15 89.64 <0.0001
Tree(TRT) 67 4.3 <0.0001
Section 2 410.29 <0.0001
TRT*Section 30 5.31 <0.0001
Flowers per bud
Source df F P>F
TRT 15 30.84 <0.0001
Tree(TRT) 67 1.76 0.0028
Section 2 83.64 <0.0001
TRT'Section 30 3.78 <0.0001
Metamer lengths
Source df F P>F
TRT 15 1.62 0.0775
Tree(TRT) 65 1 .78 0.0028
Section T 2 395.61 <0.0001

TRT*Section 30 0.73 0.8395

 

42

 

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43

Table 2-7. Analysis of variance for percentages of blind nodes, single
vegetative axillary buds, lateral shoots, and spurs from different
rootstock treatments and from different sections within the two-year-
old ‘Hedelﬁnger’ shoots of those treatments. Analyzed data were
collected during the 2001 growing season.

 

 

 

 

 

 

 

 

 

 

 

Blind nodes

Source df F P>F
TRT 15 4.58 <0.0001
Tree(T RT) 61 1.92 <0.0001
Section 2 199.86 <0.0001
TRT*Section 30 3.55 <0.0001
ﬂetative axillary buds

Source df F P>F
TRT 15 78.99 <0.0001
Tree(TRT) 61 1.97 <0.0001
Section 2 206.88 <0.0001
TRT‘Section 30 7.85 <0.0001
Lateral shoots

Source df F P>F
TRT 15 6.25 <0.0001
Tree(TRT) 61 1.68 <0.0001
Section 2 782.82 0.0017
TRT*Section 30 4.99 <0.0001
Spurs

Source df F P>F
TRT 15 57.76 <0.0001
Tree(TRT) 61 2.23 <0.0001
Section 2 155.26 <0.0001
TRT*Section 30 10.82 <0.0001

 

 

Table 2-8. The effect of rootstock, listed in order of increasing vigor, on
relative amounts of different node types (blind node, single vegetative
axillary bud, lateral shoot, and spur) in the proximal section of the two-
year-old shoots of ‘Hedelfinger’ sweet cherry. Shoots were analyzed as
three sections (proximal, medial, and distal) of equal length. Counts
were taken in the 2001 growing season, and are reported in each column
as percentage of the total number of nodes (:1: standard errors).

number of

blind vegetative shoots spurs nodes
(:1. 209/1 72 1 7.5 8 1 3.2 0 20 1 6.3 4 1 0.3
Edabriz 36 1 9.3 64 1 9.3 0 0 1 0.0 5 1 0.3
W. 53 37 1 7.9 47 i 8.7 O 16 i 7.1 4 i 0.2
W. 72 34110.1 53110.4 0 1316.0 510.3
(:1. 5 27 1 5.8 48 1 7.0 0 25 1 7.3 4 1 0.4
GL7 51110.4 1317.8 0 36: 10.3 410.4
G1. 195/20 28 1 6.4 9 1 4.6 0 62 1 5.3 5 1 0.4
GL6 2718.8 2619.0 0 48111.4 510.4
W. 158 25 1 7.6 72 1 7.5 0 4 1 3.8 4 1 0.3
W. 10 31110.5 66110.1 0 212.3 510.5
W. 13 28 1 7.8 72 1 7.8 0 0 1 0.0 5 1 0.4
Mazzard 37 1 8.2 63 1 8.2 . 0 o 1 0.0 5 1 0.9
Mahaleb 15 1 6.7 85 1 6.7 0 o 1 0.0 7 1 0.8
MM 2 25 1 6.7 75 1 6.7 0 0 1 0.0 6 11.7
MxM60 1213.5 8813.5 0 010.0 410.9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

45

 

Table 2-9. The effect of rootstock, listed in order of increasing vigor, on
relative amounts of different node types (blind node, single vegetative
axillary bud, lateral shoot, and spur) in the medial section of the two-
year-old shoots of ‘Hedelfinger’ sweet cherry. Shoots were analyzed as
three sections (proximal, medial, and distal) of equal length. Counts
were taken in the 2001 growing season, and are reported in each column
as percentage of the total number of nodes (:1: standard errors).

 

number of

blind vegetative branches spurs nodes
Gi. 209/1 16 1 5.5 14 1 4.5 1 1 0.8 69 1 8.8 6 1 0.5
Edabriz 2 1 1.8 47 1 8.0 0 1 0.0 51 1 7.8 8 1 0.5
W. 53 0 1 0.0 20 1 8.0 0 1 0.0 80 1 8.0 7 1 0.5
W. 72 7 1 7.4 26 1 7.4 0 1 0.0 66 1 8.6 8 1 0.5
Gi.5 311.9 1214.0 713.6 7816.0 710.8
GL7 010.0 613.1 311.7 9213.2 610.5
Gi. 195/20 0 1 0.0 3 1 1.9 1 1 0.8 97 1 2.0 7 1 0.5
GL6 211.5 110.8 312.1 9412.5 910.6
W. 158 1 1 0.8 55 1 9.2 0 1 0.0 45 1 9.2 7 1 0.6
W. 10 211.6 66110.1 010.0 32110.1 810.8
W. 13 5 12.6 8913.8 010.0 713.6 910.7
Mazzard 0 1 0.0 98 1 1.6 2 1 1.6 0 1 0.0 9 1 0.9
Mahaleb 1 1 1.0 93 1 3.9 0 1 0.0 6 1 3.4 11 1 0.8
MXMZ 714.3 9314.3 010.0 010.0 1011.2
MxM 60 5 1 2.8 95 1 2.8 0 1 0.0 O 1 0.0 6 1 0.7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

46

 

Table 2-10. The effect of rootstock, listed in order of increasing vigor,
on relative amounts of different node types (blind node, single
vegetative axillary bud, lateral shoot, and spur) in the distal section of
the two-year-old shoots of ‘Hedelfinger’ sweet cherry. Shoots were
analyzed as three sections (proximal, medial, and distal) of equal length.
Counts were taken in the 2001 growing season, and are reported in each
column as percentage of the total number of nodes (:1: standard errors).

number of

blind vegetative shoots spurs nodes
Gi. 209/1 111.0 211.5 6615.4 3115.0 710.3
Edabriz 1 1 0.9 2 1 1.0 38 1 5.2 59 1 5.4 9 1 0.5
W. 53 0 1 0.0 1 1 0.6 47 1 5.0 53 1 4.9 9 1 0.5
W. 72 2 11.7 11 0.8 43 1 5.5 54 1 5.5 10 1 0.7
61.5 111.2 110.7 6614.8 3214.7 810.9
Ci. 7 0 1 0.0 0 1 0.0 46 1 9.0 54 1 9.0 8 1 0.7
Gi.195/20 010.0 111.0 311 5.9 6816.1 810.5
GL6 412.6 211.2 4718.5 4718.3 1211.5
W. 158 8 1 5.2 5 1 2.5 38 1 5.9 50 1 6.3 9 1 0.5
W. 10 211.4 1815.4 2714.5 5215.0 910.7
W. 13 3 1 1.5 30 1 6.4 38 1 4.0 29 1 6.2 10 1 0.5
Mazzard 1 1 0.8 60 1 4.6 36 1 4.8 3 1 1.2 11 1 0.9
Mahaleb 5 1 3.2 34 1 6.0 26 1 6.1 35 1 3.9 14 1 0.8
MXMZ 211.2 6514.7 2415.3 814.8 1211.7
MxM 60 5 1 2.3 56 1 3.7 30 1 4.4 9 1 4.0 7 1 0.9

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

47

 

located in the medial section, with the exception of lateral shoots, which were still
relatively few (Table 2-9). Blind nodes were also less common. On most of the
rootstocks, shoots had < 7 % blind nodes; only Gi. 209/1 had a considerable amount, with

16 % of the total nodes being blind.
Trunk Cross-Sectional Area Increase and Spur Flowering Characteristics

Trunk cross sectional area increase (TCSAI) is an indicator of tree vigor or
size. With the use of TCSAI, tree size at planting can be eliminated as a variable, and
relative vigor in a single year can be quantiﬁed. The spur ﬂowering characteristics
assessed in this study (ﬂower number per spur, and ﬂower number per bud) were plotted
against TCSAI during 1999 (the year that the shoots grew) and TCSAI during 2000 (the
year that the ﬂowers were initiated). The R2 values for the relationship between ﬂoral
bud number per spur and TCSAI were similar for 1999 and 2000. The regression
equation describing ﬂoral bud number per spur to TCSAI was more linear in 2000.
However, the R2 values for the relationship between ﬂower number per bud and TCSAI
were higher for 2000 than 1999. Therefore, only the relationships for spur ﬂowering
characteristics versus 2000 TCSAI will be shown.

No strong relationship was found between TCSAI and ﬂower number per bud or
bud number per spur in the proximal section (Figures 2-3, 2-4). The ﬂoral bud number
per spur in the medial section was related more to 2000 TCSAI (Figure 2-3) than to 1999
TCSAI (data not shown). Flower number per bud in the medial section also had a
stronger relationship to 2000 TCSAI (Figure 2-4). Bud number per spur in the distal
section showed the greatest relationship to TCSAI, with 2000 TCSAI having the highest

R2 (0.70) (P<0.0001) (Figure 2-3). This trend did not hold true for the ﬂower number

48

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50

per bud in the distal section, since 1999 TCSAI was related more to ﬂower number per

bud (data not shown) than was 2000 TCSAI (Figure 2-4).
Flowers per Bud vs. Buds per Spur

Average ﬂower number per bud was plotted against the ﬂoral bud number per
spur, across all rootstocks. In all sections, the relationship between ﬂower formation and
bud formation was positive and strong (Figure 2-5). Rootstock affected both variables,

with the strongest relationship (R2 = 0.93) in the medial section (P<0. 0001).

DISCUSSION

It is important to be able to predict the location and ﬂowering characteristics
of spurs within the canopy (Lespinasse and Lauri, 1996; Crabbe, 1984). A general
conclusion of our study is that rootstock inﬂuenced both spur ﬂoral characteristics (bud
number per spur and ﬂower number per bud) and location of spurs along the shoot,
results that also occurred in the ‘Montmorency’ trial (Chapter Three). This could be
attributed, at least partially, to the rootstock effect on tree size (vigor); however,
differences in TCSAI only accounted for ~ 2/3 to 3/4 of the variability in spur ﬂoral
characteristics for ‘Hedelﬁnger’ sweet cherry.

In the Gisela / Giessen series, bud number per spur and the ﬂower number per bud
increased as tree size increased (Table 2-2), while those parameters generally decreased
in other rootstocks as size increased. The importance of this ﬁnding is that when
selecting rootstocks for a balanced vegetative to reproductive ratio, more must be
considered than simply TCSAI or tree size, such as location of the spurs and quantity of

ﬂowers produced per spur.

51

 

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52

Another major effect of rootstock on spur ﬂowering characteristics was the
difference in numbers of ﬂowers per bud and buds per spur between the proximal and
distal sections of the two-year-old shoot. The two-year-old shoot had both the
characteristic of being the ﬁrst location of spur growth, as well as an indicator of where
spurs will be produced in the future. Location within this two-year-old section affected
both spur ﬂowering characteristics. It seems reasonable that in larger trees with more
dense canopies, the more proximal sections of the shoots would have fewer spurs because
of within-canopy shading. However, in our trial, the trees were only in their fourth year,
and therefore small enough to have very little within-canopy shading. Assuming there
was not a strong effect of light, the increase in number of ﬂowers per bud and buds per
spur in the distal sections of the shoot relative to the proximal were probably due to
internal or genetic factors. In the ‘Montmorency’ trial, the bud number per spur and
ﬂower number per bud were greatest in the proximal section, supporting the theory that
the spur ﬂowering characteristics were due to internal or genetic factors (Chapter Three).

Average metamer length did not predict metamer type in our study since, among
rootstocks, there were differences in percentages of different metamers within each
section (Figure 2-2), even though metamer length was the same among rootstocks.
However, a limitation existed in the way that metamer length was assessed. The number
of nodes was counted per section and the length of that section was taken. Metamer
lengths were not equal throughout the shoot section (personal observation). In some
cases, a very short metamer was adjacent to a long metamer. Because of this, a more
accurate presentation of these lengths might be relative phyllotactic length. The length

can only be relative since the actual number of phyllotactic units was not counted, and it

53

must be assumed that nodes had the same orientation among rootstocks. An interesting
observation would be to look at phyllotactic differences among rootstocks.

Even though average metamer length was the same between rootstocks, some
general conclusions can be made about the location of different metamer types within the
shoot. For trees on all rootstocks, there were no lateral shoots in the proximal sections.
The medial sections also had a very small amount of lateral shoots. Almost all of the
metamers in the proximal sections of trees smaller than those on W. 158 were lateral
shoots. Determining the location of different metamers within the shoot based on
dividing the total section lengths into thirds may be a useful, if artiﬁcial, way to divide
the shoot, and so could be useful in developing training sytems for different rootstocks.
Earlier work in apple by Lespinasse and Lauri (1996) showed that neither distal nor
proximal node number orientation predicted node type accurately.

Knowing the location of spurs and the spurs ﬂowering characteristics could be
helpful in managing the tree. The one variable not measured, which may be useﬁJl for
future work, is the evolution of the branch, or how spurs within a branch age. We did not
look at the way that the metamer types and quality change in these shoot sections over
time, particularly as the tree canopy matures. This is also a major factor in tree
management, since rootstock may also affect how the spurs age.

The effect of rootstock on spur ﬂowering characteristics, independent of its effect
on tree size, underscores the value of more accurate assessment of spur ﬂowering
characteristics on different rootstocks. Lespinasse and Lauri (1996) have noted that

prediction of the distribution of speciﬁc metamers is one the three variables that must be

54

understood before an accurate prediction and assessment of the tree’s productive
potential can be found. This is currently a critical step in the evaluation and adaptation of

new precocious and/or vigor-controlling rootstocks for sweet cherry production.

 

55

LITERATURE CITED

Cowgill, W. and J. Clements. 2002. NC-14O regional rootstock research project. NC-
140. <httn://www.nc140.org > 23 September 2002.

Crabbe, J .J . 1984. Vegetative vigor control over location and fate of ﬂower buds in ﬁ'uit
trees. Acta Horticulturae 149: 55-63.

Franken-Bembenek, S. and W. Gruppe. 1985. Effect of different hybrid rootstocks on
growth and yielding characters of sweet cherries. Acta Horticulturae 169: 219-226.

Godin, C. and Y. Caraglio. 1998. A multiscale model of plant topological structures.
Journal of Theoretical Biology 191: 1 - 46.

Guimond, C., P. Andrews, and GA. Lang. 1998. Scanning electron microscopy of ﬂoral
initiation in sweet cherry. Journal of the American Society of Horticultural Science
123(4): 509-512.

Lang, GA. 2000. Precocious, dwarﬁng, and productive — how will new cherry
rootstocks impact the sweet cherry industry? HortTechnology 10: 719 — 725.

Lespinasse, J .M. and RE. Lauri. 1996. Inﬂuence of ﬁ'uiting habit on the pruning and
training of apple trees. Compact Fruit Tree 29: 7 5-82.

SAS Institute. 1989. SAS/STAT User’s Guide, Version 6. (SAS Institute, Cary, NC).

Schaumberg, G. and W. Gruppe. 1985. Growth and fruiting habit of Prunus avium cv.
‘Hedelﬁnger’ on clonal cherry hybrid rootstocks. Acta Horticulturae 169: 227-234.

Schultz, EA. and G.W. Haughn. 1991. LEAFY, a homeotic gene that regulates
inﬂorescence development in Arabidopsis. The Plant Cell 3: 771-781.

Westwood, MN. and AN. Roberts. 1970. The relationship between trunk cross-
sectional area and weight of apple trees. Journal of the American Society of Horticultural
Science 95(1): 28-30.

White, J. 1984. Plant metamerism. In Perspectives in plant population ecology. Dirzo,
R. and J. Sarukhan, eds. Sinamar Associates Incorporated, Sunderland, Mass. pp. 15-47.

Wustenberghs, H. and J. Keulemans. 2000. Groenprincipen en groenmanipulatie bij
steenfruit. Katholieke Universiteit Leuven, Brussels, 198 pp.

56

CHAPTER THREE
Rootstock Affects Floral Distribution and Patterning in ‘Montmorency’

Tart Cherry

57

Rootstock Affects Floral Distribution and Patterning in ‘Montmorency’ Tart

 

Cherry.
ABSTRACT
The NC-14O regional tree fruit rootstock project established a trial of cherry .
rootstocks across North America in 1998 to test their performance with the tart cherry
scion ‘Montmorency’. One ‘Montmorency’ trial was established near Traverse City, MI.
This plot was used to characterize rootstock inﬂuence on the development of ﬂowers, ;

buds, spurs, blind nodes, and lateral branches on two-year-old shoots. “Both rootstock
genotype and node location on the shoot inﬂuence bud number per spur and ﬂower
number per bud. Both ﬂoral bud number per spur and ﬂower number per bud were
inﬂuenced, in general, by rootstock. This effect was not completely due to the
rootstock’s effect on scion vigor. For the Gisela/Giessen and Weiroot series of
rootstocks, the ﬂower nmnber per bud and bud number per spur increased with increasing
vigor with the exception of Gi.6, whereas the other rootstock had decreasing ﬂowers per
bud and buds per spur with increasing vigor. Both variables had the lowest values in the
distal areas of the shoot, which is opposite that in ‘Hedelﬁnger’ sweet cherry (Chapter
Two). Rootstock genotype inﬂuenced location of lateral shoots, ﬂoral buds, and axillary
vegetative buds within two-year-old shoots; however, the location Of blind nodes was not
affected by rootstock. Blind nodes occurred in all sections. These characteristics are
useful for evaluating, and ultimately managing, production of ‘Montmorency’ tart cherry

on rootstocks that alter scion precocity and/or vigor.

58

INTRODUCTION

Cherry rootstocks have been selected for various reasons, including precocity,
productivity, vigor control, disease tolerance, and adaptability to different soils. With
some of these rootstocks, there is a potential problem of excessive cropping levels when
grafted to very productive scion cultivars. Excessive cropping can result in poor fruit
quality and stunted vegetative growth (Lang, 2000). In tart cherry, one of the potentially
major problems associated with dwarﬁng rootstocks is the large proportion of ﬂowers on
the one-year—old laterals (Perry, 1996). On dwarﬁng rootstocks, there may be less growth
and so less fruiting, since the ﬁ'uiting potential is dictated by the annual vegetative
growth that occurs. One approach to study this phenomenom, and potentially develop
strategies to manage it, is to more precisely characterize how rootstock genotype
inﬂuences tree architecture and ﬂower placement on the Scion; that is, how the
development of different nodes can be used to assess how nodes are affected
differentially within a shoot. '

Pattern can be studied within a tree by dividing the tree either artiﬁcially, e.g.,
empirically dividing a shoot into equal units of length, or naturally, e. g., using biological
growth parameters that are repeated throughout the tree or have an identical nature
(Godin and Caraglio, 1998; White, 1984). Growth of angiosperrn shoots can be
described as a series of repeating units (metamers) that are formed sequentially by the
apical meristem. In the most basic form, a metamer consists of a node with an associated
leaf-like organ, a lateral meristem in the axil of the leaf, and the proximally located
internode (White, 1984). It has been suggested that there is an ordered pattern of

different metamers (Schultz and Haughn, 1991).

59

 

Distribution of different metamers within the plant plays a large part in the
productive potential of tree ﬁ'uit species (Lespinasse and Lauri, 1996). Metamer types in
sweet cherry include blind nodes, lateral shoots, single vegetative buds, and spurs.
Lespinasse and Lauri suggested that studying the patterns and distribution of different
metamer types in fruit trees would result in several practical applications including the
development of new tree growth habits through breeding, new training systems that t’
reduce pruning and thinning, and a more rational approach to cultivation that could lead

to an improvement in hit quality characteristics. A better ability to predict ﬂower

 

location would also provide a more deﬁnitive base for the study of ﬂower bud ‘quality’
(Crabbe, 1984).

Rootstocks are known to affect spur characteristics. Franken-Bembenek and
Gruppe (1985) found that yield potential in sweet cherry was mainly dependent on
rootstock. One of the main ways rootstock altered yield potential was by altering
location of spur insertions. Schaumberg and Gruppe (1985) tested ‘Hedelﬁnger’ sweet
cherry on some of the Giessen series rootstocks, and observed that the number of buds
per spur was not altered, but that the number of ﬂowers per bud was greatly affected by
rootstock. The number of ﬂoral buds per spur depended greatly on the position of the
spurs within the shoot. More distally located spurs produced a greater number of buds
per spur. Other correlations have been made between location of the spur and the number
of ﬂoral buds per spur in sweet cherry cultivars, indicating that position within the shoot
affects spur ﬂowering characteristics (Wustenberghs and Keulemans, 2000).

The limitations of the above trials were that they were done on a limited

number of rootstocks, some rootstocks not in the trial may be more ideal for conditions in

60

Michigan, and most of the trials were not done with tart cherry. Location of different
metamer types has not received a lot of attention in tart cherry trees, since they are
harvested mechanically. With the recent US. introduction of a new tart cherry with fresh
market potential, ‘Balaton’, it would be beneﬁcial to understand how rootstocks affect
tart cherry tree habit. A regional tree ﬁ'uit rootstock (N C-140) trial has been established
in the US to evaluate rootstocks for suitability in the US. Rootstock can signiﬁcantly
inﬂuence ﬂower density, as well as vigor and yield efﬁciency. This is not enough
information, however, to predict where the ﬂowers will be borne within the canopy,
which is important for predicting and managing the productive potential of the tree.

Spurs are ﬁrst produced in the two—year-old shoot sections in tart cherry.
This is because tart cherries initiate ﬂowers in the summer before ﬂowering occurs, after
active growth has ceased (Diaz etal., 1981). The two-year old shoot section, then, is a
good predictor of the distribution of different metamer types since it is the ﬁrst area
where spurs form.

Schaumberg and Gruppe (1985) reported that the effect of rootstock on the
number of ﬂoral buds per spur was small on ‘Hedelﬁnger’ sweet cherry, but that there
was a signiﬁcant effect on the number of ﬂowers per bud. They also noticed that the
number of buds per spur was correlated strongly with the location of the spur within the
branch. The number of buds per spur increased distally along two-, three-, and four- year
old shoots.

Schaumberg and Gruppe’s (1985) trials were in Germany, and so may not have
accurately assessed rootstocks and scions examined in trials in the US. The objectives

for this experiment were: (1) to assess the effect of rootstock and node location within

61

two-year old wood on spur ﬂowering characteristics (ﬂower number per bud and ﬂoral
bud number per spur) and (2) to assess the effect of rootstock on location of the different
metamer types (blind nodes, single vegetative buds, lateral shoots, and spurs) in

‘Montmorency’ tart cherry.

MATERIALS AND METHODS

Plant Materials

As part of the NC-14O regional tree fruit rootstock project, a plot of
‘Montmorency’ tart cherry (Prunus ceraus L.) trees on 12 rootstocks was established in
spring 1998 at Michigan State University’s Northwest Horticultural Research Station
(NWHRS) near Traverse City, Michigan. The trees were planted in an Emmet-Leelenau
sandy loam in a randomized complete block design with 8 replications; however, a
completely randomized design was used for this study since 12 rootstocks (see Table 3-1)
and only 5 replications were used. The trees were trained to a modiﬁed central leader
and drip irrigated. Fertilization and protective sprays were applied as by local standard
recommendations.

Five trees per rootstock were selected in early spring 2001. Three shoots of
comparable size and including second year wood were selected from each tree’s central
leader. Markings were made using paint so that the second-year section of each shoot

was divided into three equal sections (proximal, medial, and distal) (Figure 3-1).

62

 

 

8. 5.88 5.2.9.. ... 8:... «...... as. 395m 3:8 ...... 5:8 .222). .223).

 

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mm .3325 .... b.5850 .5....o.52.53 o. .>> c. 59.53
. n .3555 .... X 55555 ... b.5550 .5320 ona. .0 ona. 535.0
S 55528 N X .3555 .& b.5850 685.0 m .0 v 5.3.0
.0 3.8.5 .o. b.5850 .55855253 Q. .>> an 5853
mm 38.8 .5 .5550 5.33553 5..... .... 88......
Va 255555 .... .... 3.855 N .5850 585.0 5 .0 5 38.0
.v 55523 ... X 3.355 N b.5550 .5520 m .0 m 5.3.0
ow 3.355 ... .5850 .5:..5.....5..53 mm .>> mm 59.5?
on .3555 .& 2M7... 8.5.... Ntnacm ntﬁvm.
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3

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63

 

Dc

Sh!

p1;

V6

"6?:
COM!

mm

m

m .\'o

Data Collection

In 2001, data for each node along the two-year-old section of each tagged
shoot were collected throughout the season. Each node was characterized according to its
placement within the shoot section and its type. Node types used for this study were: (1)

vegetative (axillary) bud; (2) spur; (3) lateral (axillary) shoot (or lateral); and (4) blind

 

If
node. t
Vegetative buds had two fates by the end of active grth that were easily
distinguishable: 1) bud break occurred late in the 2001 season and a lateral shoot formed,
or 2) the bud produced only leaves during the 2001 season, and so remained only a E

vegetative bud. Whether the bud remained vegetative or became a lateral shoot in 2001
was not assessed in this study. Assessment of the distribution of vegetative buds
included all that were vegetative at the beginning of the season.

Three spur parameters were measured. Bud number in each spur was counted
in April 2001 and the number of ﬂoral buds was determined by subtracting one (for the
vegetative bud) ﬁom the total buds within the spur. Flowers within each spur were
counted in spring 2001. Flower number per bud was estimated by dividing the ﬂower
number per spur by the ﬂoral bud number per spur.

The only parameters measured on nodes with lateral shoots were length of
growth that occurred during 2000, and length of grth that occurred during 2001 (made

in November 2001, after active growth had ceased and the leaves had dropped). Metamer

 

.5522... as? 52.... o... 5.....» .... 55.53.
595...... o... 85...... no...— vom .523 ...—5.5 ...—5.59.55 55.5%.. .5... 25.59.55 a 5 5.5.35... ..-m 9...»...

uoosm
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65

lengths were estimated for each section (proximal, medial, distal). Since shoots were

 

split into three equal sections, the estimate was done using the following equation:

total section length
number of nodes within th e section

Metamer length (section) -=-

 

Blind nodes were considered to be those that did not exhibit any active growth,
whether vegetative or reproductive. Although there are different reasons for blind node
development (Wustenberghs and Keulemans, 2001), these were not ascertained in this .1

study. Most blind nodes of sweet cherry are due to the formation of solitary ﬂower buds

 

at the base of one-year-old shoots, so blind nodes in this study are most likely due to 3.
ﬂowering during 2000 in the tagged shoots. H
Trunk cross-sectional area (TCSA) is an indicator of tree size (Westwood and
Roberts, 1970). Trunk cross-sectional area increase (TCSAI), then, indicates vigor of the
scion. TCSAI measurements used in this study were taken as part of the NC-l40 regional
tree research project (Win and Jon, 2002).
Statistical Analysis
Statistical analyses were performed using the SAS proc glrn program (SAS
Institute, 1989). In all studies, pairwise comparisons and the analysis of variance were
used in the comparisons among rootstocks. When comparing effects of rootstock on
metamer location and ﬂowering characteristics, all values were expressed as mean i
standard error. Statistical signiﬁcance was calculated using Student’s t-test. For the

regression analyses, highest R2 was used to determine the best ﬁtting regression curve.

66

RESULTS

Floral Bud Number per Spur

In general, the more vigorous rootstocks had more ﬂoral buds per spur (Table
3-2). Spur formation occurred in all sections, except for the distal part of Gi.209/1
(which had no ﬂoral buds per spur) (Table 3-3, 3-4, 3-5). Spur location within the shoot
section also correlated with ﬂoral bud number per spur. The highest number of ﬂoral
buds per spur occurred in the medial section, and the lowest in the distal section. The
ﬂoral bud number per spur increased with increasing tree size to a point and then
decreased (Figure 3-2).
Flower Number per Bud

Rootstock affected the ﬂower number per bud, and the more vigorous
rootstocks generally had more ﬂowers per bud (Tables 3-4). The fewest ﬂowers per bud
were in the distal sections (Table 3-5). In the smaller trees, there were generally more
ﬂowers per bud in the proximal section, while in the trees larger than those on Gi.7, the

higher number of ﬂowers per bud occurred in the medial section (Figure 3-3).
Metamer Lengths

Metamer lengths did not differ signiﬁcantly among rootstocks, but did by
location within the shoot (Table 3-6). The differences in metamer lengths were strongly
related to location within the shoot. The main difference was observed between the
proximal and distal sections, as well as between the medial and distal sections. Average
metamer lengths were: 3.8 :t 0.09 for the proximal, 2.7 i 0.04 for the medial, and 2.2 i

0.04 for the distal sections. Metamer lengths in the proximal section ranged from 3.2 cm

67

 

 

 

f' K

lab]
the:
stan
‘Mo
seas

Table 3-2. The effect of rootstock, listed in order of increasing vigor, on
the average number of ﬂowers per bud and ﬂoral buds per spur (:I:

standard error) on the entire two-year-old shoot section of

‘Montmorency’ tart cherry. Counts were taken in the 2001 growing

season.

Edabriz
W. 53
Ci. 5
Ci. 6

W. 158
W. 72

Gi. 7

Ci. 195/20
W. 10

W. 13
Mahaleb

Buds per spur Flowers per bud

 

 

 

 

 

 

 

 

 

 

 

 

 

23:04 21:04
35:05 23:03
22:04 17:04
30:06 20:04
32:04 26:04
37:03 28:03
33:0A 27:03
39:04 30:03
3J:OA 25:03
32:05 20:03
32:03 27:02

 

68

 

 

 

 

lab
the
Sill
“ll
sea

Table 3-3. The effect of rootstock, listed in order of increasing vigor, on
the average number of ﬂowers per bud and ﬂoral buds per spur (:I:
standard error) in the proximal part of two-year-old shoot section of
‘Montmorency’ tart cherry. Counts were taken in the 2001 growing
season.

Buds per spur Flowers per bud

 

 

 

 

 

 

 

 

 

 

 

 

 

ELM

2.4: 1.0 15:05
Edabriz 2.3 : 0.4 2.8 i 0.5
W. 53 4.3 : 0.5 3.0 :l: 0.2
Gi. 5 3.2 :I: 0.3 2.7 :l: 0.5
Gi. 6 3.9 i 0.3 3.0 1: 0.2
W. 158 3.5 : 0.3 3.4 :l: 0.3
W. 72 3.4 :l: 0.4 3.4 :I: 0.3
Gi. 7 3.8 :l: 0.3 3.7 : 0.4
Gi. 195/20 4.0 : 0.1 3.4 d: 0.5
W. 10 3.6 :l: 0.3 2.7 :l: 0.2
W. 13 3.6 :l: 0.4 2.3 :I: 0.2
Mahaleb 2.6 d: 0.4 2.8 : 0.1

 

69

 

 

 

 

labl
the:
Stan
‘llh
seas

Table 3-4. The effect of rootstock, listed in order of increasing vigor, on
the average number of ﬂowers per bud and ﬂoral buds per spur (:
standard error) in the medial part of two-year-old shoot section of
‘Montmorency’ tart cherry. Counts were taken in the 2001 growing

season.

Gi. 209/1

Edabriz

W. 53

Gi. 5

Ci. 6

W. 158

W. 72

Gi. 7

Gi. 195/20

W. 10

W. 13

Mahaleb

. Buds per spur Flowers per bud

 

 

 

 

 

 

 

 

 

 

 

 

 

10:10 06:06
39:08 30:06
47:07 29:05
27:08 20:06
35:14 20:0]
47:03 33:02
49:02 33:0J
40:06 29:05
53:04 36:02
49:04 34:03
49:02 23:0J
40:04 29:02

 

 

 

70

and

 

labl

the:
stan
‘hlo
seas

Table 3-5. The effect of rootstock, listed in order of increasing vigor, on
the average number of ﬂowers per bud and ﬂoral buds per spur (:1:
standard error) in the distal part of two-year-old shoot section of
‘Montmorency’ tart cherry. Counts were taken in the 2001 growing
season.

Buds per spur Flowers per bud

 

 

 

 

 

 

 

 

 

 

 

Gi. 209/1 0.0 : 0.0 0.0 : 0.0
Edabriz 0.8 : 0.4 0.6 : 0.3
W. 53 1.4 : 0.6 0.8 : 0.4
Gi. 5 0.6 : 0.6 0.4 : 0.6
Gi.6 1.7:10 1.1:0.7
W. 158 l.7:0.8 1.1 :06
W. 72 2.8 : 0.8 1.7 : 0.5
Ci. 7 1.9 : 0.6 1.4 : 0.4
Gi. 195/20 2.4 : 0.7 1.9 : 0.7
W. 10 2.6 : 0.9 1.5 : 0.6
W. 13 1.2 : 0.8 0.7 : 0.5
Mahaleb 3.1 : 0.8 2.3 : 0.7

 

 

 

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72

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73

 

 

Tab.
ﬂow
trea
(hos

grm

a Ilf" 115-=1

T'eef‘

Table 3-6: Analysis of variances for the number of buds per spur,
ﬂowers per bud and metamer lengths from different rootstock
treatments and from different sections within the two-year-old shoots of
those treatments. Analyzed data were collected during the 2001
growing season.

 

 

 

 

 

 

 

 

Buds per spur

Source df F ‘ P>F
TRT 11 4.91 <0.0001
Tree(TRT) 52 1 .38 0.0817
Section 2 48.35 <0.0001
TRT‘Section 22 1 .2 0.2636
Flowers ger bud

Source df F P>F
TRT 11 8.83 <0.0001
Tree(TRT) 52 2.52 <0.0001
Section 2 89.32 <0.0001
TRT‘Section 22 1 .33 0.1713
Metamer Length

Source df F P>F
TRT 11 3.24 0.0003
Tree(TRT) 52 2.04 <0.0001
Section 2 328.45 <0.0001

TRT‘Section 22 2.25 0.001

74

 

(Gi.209/1) to 4.3 cm (W.13), while the range was from 1.8 (Gi. 209/ 1) to 2.6 (W.13) in
the distal section.
Distribution of Metamer Types

Distributions of four different metamer types (blind node, vegetative axillary
bud, lateral shoot, spur) were analyzed as a percentage of the total number of metamers
within each section (proximal, medial, and distal) (Figure 3—4). A signiﬁcant effect of !
rootstock was observed in the relative amounts of vegetative (axillary) buds, blind nodes,

and spurs (Table 3-7). However, rootstock genotype did not affect the percentage of

lateral shoots. Location within the shoot affected distribution of metamer types. Very

 

few vegetative (axillary) buds were present in any of the rootstock treatments or sections;
in the medial and distal sections, vegetative buds never exceeded 5 % of the total
metamers present (Tables 3-8, 3-9). Blind nodes were found in all sections. The greatest
percent of nodes in the medial section were either lateral shoots or spurs, and in the distal
section were lateral shoots and blind nodes (Figure 3-4). A relationship between vigor

and distribution of speciﬁc metamer types was not apparent.
Trunk Cross-Sectional Area Increase and Spur Flowering Characteristics

Trunk cross sectional area increase (TCSAI) is an indicator of tree vigor or
tree size. With the use TCSAI, tree size at planting can be eliminated as a variable, and
relative vigor in a single year can be quantiﬁed. The spur ﬂowering characteristics
assessed in this study (ﬂoral bud number per spur, and ﬂower number per bud) were
plotted against TCSAI during 1999 (the year that the shoots grew) and TCSAI during
2000 (the year that the ﬂowers were initiated). Only spur ﬂowering characteristics

plotted against 2000 TCSAI are presented. For both 1999 and 2000, there was no

75

 

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Table 3-7. The effect of rootstock, listed in order of increasing vigor, on
relative amounts of different node types (blind node, single vegetative
axillary bud, lateral shoot, and spur) in the distal section of the two-
year-old shoots of ‘Montmorency’ tart cherry. Shoots were analyzed as
three sections (proximal, medial, and distal) of equal length. Counts
were taken in the 2001 growing season. Numbers reported in each
column are percents of the total number nodes (:1: standard errors).

 

 

 

 

 

 

 

 

 

 

 

 

number of

blind vegetative shoots spurs nodes
Gi. 209/1 83 : 6.0 0 : 0.0 17 : 5.9 0 : 0.0 6 : 0.7
Edabriz 47 : 9.5 0 : 0.0 52 : 8.8 1 : 1.0 6 : 0.4
W. 53 28:11.7 0:0.0 66:96 6:31 8:05
Gi.5 44:15.5 0:0.0 54:15.1 1:15 6:07
Gi. 6 34 : 14.9 0 : 0.0 50 : 7.5 16 : 10.2 7 : 0.4
W. 158 33 : 8.9 0 : 0.0 62 : 5.9 5 : 5.2 7 : 0.4
W. 72 24:11.1 0:00 69:92 7:26 7:03
Gi. 7 40 :10.5 0 : 0.0 48 : 6.0 12 : 5.8 6 : 0.7
Gi. 195/20 25 : 9.2 0 : 0.0 68 : 7.5 7 : 2.6 7 : 0.3
W. 10 22:68 0:00 70:61 8:30 8:02
W. 13 21 :39 0:00 77:29 2:14 7:07
Mahaleb 22 : 6.6 2 : 1.8 69 : 3.7 7 : 3.4 8 : 1.0

 

 

 

 

 

 

77

 

Table 3-8. Analysis of variance for percentages of blind nodes from
different rootstock treatments and from different sections within the
two-year-old ‘Montmorency’ shoots of those treatments. Analyzed
data were collected during the 2001 growing season.

 

 

 

 

 

 

 

 

 

 

 

Blind nodes

Source df F P>F
TRT 11 2.53 0.0134
Tree(T RT) 47 2.36 0.0002
Section 2 32.47 <0.0001
TRT'Section 22 1 .46 0.1 096
metative axillary buds

Source df F P>F
TRT 11 3.31 0.002
Tree(TRT) 47 1.18 0.2474
Section 2 126.87 <0.0001
TRT‘Section 22 2.74 0.0004
Lateral shoots

Source df F P>F
TRT 11 1.42 0.1968
Tree(TRT) 47 1 .06 0.3972
Section 2 102.58 <0.0001
TRT‘Section 22 4.4 <0.0001
Spurs

Source df F P>F
TRT 1 1 3.25 0.0023
Tree(TRT) 47 2.05 0.0017
Section 2 178.35 <0.0001
TRT‘Section 22 3.17 <0.0001

 

78

Table 3-9. The effect of rootstock, listed in order of increasing vigor, on
relative amounts of different node types (blind node, single vegetative
axillary bud, lateral shoot, and spur) in the medial section of the two-
year-old shoots of ‘Montmorency’ tart cherry. Shoots were analyzed as
three sections (proximal, medial, and distal) of equal length. Counts
were taken in the 2001 growing season. Numbers reported in each
column are percents of the total number nodes (1 standard errors).

 

number of 93

blind vegetative shoots spurs nodes 3
Gi. 209/1 12 : 5.4 1: 1.1 79 : 8.0 8 : 8.3 3 : 0.4
Edabriz 11 :86 0:0.0 51:7.8 38:11.1 5:06
W. 53 10:6.7 1: 1.4 58:38 31 :70 7:0.5
Gi. 5 20 : 10.5 0 : 0.0 60 : 10.6 20 : 8.4 5 : 0.3
Gi. 6 11 : 7.8 0 : 0.0 47 : 18.4 42 : 22.3 5 : 0.4
W. 158 18: 11.9 0:0.0 45:15.5 37:19.9 6:0.6
W. 72 8:4.1 2:1.9 21:6.7 70:10.1 6:0.5
Gi. 7 20 : 7.2 3 : 3.0 42 : 12.3 35 : 8.0 6 : 0.3
Gi. 195/20 14 : 4.3 0 : 0.0 33 : 10.2 53 : 10.0 6 : 0.2
W. 10 2:1.3 5:3.1 17:9.2 76:8.7 6:0.4
W. 13 6:3.9 2: 1.8 23: 10.8 70: 14.5 6:0.5
Mahaleb 9 : 8.0 4 : 4.2 13 : 3.7 73 : 10.5 7 : 0.7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

79

 

 

difference in the relationship between TCSAI and ﬂoral bud number per spur. The R2
value for the relationship of ﬂower number per bud to TCSAI, however, was higher for
2000 than 1999.

The proximal section showed the strongest relationship, perhaps due to the
greater concentration of spurs in this area (Table 3-10). There is a general trend in which
both ﬂoral bud number per spur and ﬂower number per bud increased with vigor to a
point and then decreased, resulting in a curvilinear relationship between spur
characteristics and vigor. This point for both ﬂowers per bud and buds per spur occurred
at TCSAI values of ~8 cm2 (1999) and 6 to 8 cm2 (2000).

Flowers per Bud vs. Buds per Spur

Average ﬂower number per bud was plotted against ﬂoral bud number per
spur for the proximal, medial, and distal sections, across all rootstocks. Rootstock
affected both of these variables positively (Figure 3-5). The weakest relationship
occurred within the proximal section (R2 = 0.32, p=0. 05 4); the R2 values for the other
sections were higher than 0.89. As the bud number per spur increased, the number of

ﬂowers per bud also increased.

DISCUSSION

It is important to be able to predict the location and ﬂowering characteristics
of spurs within the canopy (Lespinasse and Lauri, 1996; Crabbe, 1984). Although tart
cherries ﬂower extensively on axillary buds of one-year-old lateral shoots (Thompson,

1996), only ﬂowering on spurs is sustainable. Flowering on the one-year-old lateral

8O

Table 3-10. The effect of rootstock, listed in order of increasing vigor,
on relative amounts of different node types (blind node, single
vegetative axillary bud, lateral shoot, and spur) in the proximal section
of the two-year-old shoots of ‘Montmorency’ tart cherry. Shoots were
analyzed as three sections (proximal, medial, and distal) of equal length.
Counts were taken in the 2001 growing season. Numbers reported in
each column are percents of the total number nodes (:1: standard
errors).

 

number of
blind vegetative shoots spurs nodes
Gi. 209/1

45: 16.2 10:3.2 26: 15.0 19:7.0 3:0.3

Edabriz 28 : 14.0 22 : 9.3 19 : 6.2 31 : 7.1 4 : 0.2
W. 53 11 :62 12:8.7 17:61 61 :57 4:0.4
Gi. 5 29:7.7 16:10.4 16:5.3 39:7.1 4:0.4
Gi.6 23:3.7 13:7.0 13:11.4 51:8.7 4:04
W. 158 30 : 3.9 14 : 7.8 8 : 8.3 48 : 8.0 4 : 0.6
W. 72 13 : 4.0 36 : 4.6 0 : 0.0 50 : 8.2 4 : 0.2
Gi. 7 21 :92 16:9.0 5 :5.0 58:5.9 4:0.3
Gi. 195/20 9 : 4.6 15 : 7.5 2 : 1.7 74 : 9.9 4 : 0.3
W. 10 12:41 34:10.1 4:2.3 51:10.1 5:0.2
W. 13 17 : 8.0 37 : 7.8 0 : 0.0 46 : 6.5 5 : 0.4
Mahaleb 13 : 3.8 42 : 7.5 1 + 1.4 44 : 7.7 5 : 0.7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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82

shoots does account for more precocious ﬂowering, since the earliest ﬂowering of spurs
is on two-year-old shoots (Thompson, 1996). However, dwarﬁng rootstocks have
already been shown to reduce the time to ﬂowering in ‘Montmorency’ (Perry, 1996).
Further acceleration in time to ﬂowering may not be beneﬁcial since tart cherry trees
currently are harvested mechanically, and trees must reach a certain size before they are
large enough to withstand the mechanical harvesting equipment (Nugent, 2001).

A general conclusion of our study is that rootstock inﬂuenced both spur ﬂoral
characteristics (ﬂoral bud number per spur and ﬂower number per bud), as well as the
location of spurs and lateral shoots within the two-year-old ‘Montmorency’ tart cherry
shoot. The same conclusion was also drawn from the ‘Hedelﬁnger’ sweet cherry study
(Chapter Two). This could be attributed, at least partially, to the rootstock effect on tree
size (TCSAI); however, TCSAI accounted for only 1/2 to 2/3 of the variability in spur
ﬂoral characteristics for ‘Montrnorency’ tart cherry.

In the Gisela/Giessen series, ﬂoral bud number per spur and ﬂower number per
bud increased as tree size increased (Table 3-2). This trend also occurred in the Weiroot
series, although to a lesser extent compared to the Gisela series.

The balance between vegetative and reproductive growth is important for reasons
other than ﬁ'uit size and yield. Overcropping is thought to be one of the contributing
factors to the soft tart cherry problem in Michigan (N ugent, 2001). Vigorous Weiroot
and Gisela/Giessen rootstocks alleviate some of this problem, since with an increase in
reproductive growth, there is also an increase in vegetative growth.

Another major effect of rootstock on spur ﬂowering characteristics was the effect

of location on both numbers of ﬂowers per bud and buds per spur. The two-year-old

83

shoot had both the characteristic of being the ﬁrst location of spur growth, as well

as an indicator of where spurs will be produced in the future. In tart cherries, it is
important to identify spur location as well as how many buds and ﬂowers occur on that
spur. Location within the two-year-old shoot affected both spur ﬂowering characteristics.
A lower ﬂoral bud number per spur and ﬂower number per bud were found in the distal
sections of all rootstock treatments (Table 3-5), which is probably due to the very low
quantity of spurs in this area (Figure 3-4).

Metamer length did not predict metamer type in our study. Metamer length
differed not only between treatments, but also between sections and was different
according to the section x treatment interaction. Metamer length did decrease distally
along the shoot in ‘Montmorency’, as well as in ‘Hedelﬁnger’, but there does not appear
to be a relationship between this change in metamer length and location or quantity of
any of the metamer types assessed (Figure 3-4; Chapter Two).

General conclusions can be made about where certain metamers are located, or
where certain metamer types are not found. For example, vegetative axillary buds are not
found in the medial or distal sections. Very few, if any, lateral shoots are found in the
proximal section, except on the less vigorous rootstocks, which could be due to the
shorter length of the two-year-old shoot. It is also interesting to note that blind nodes are
found in all sections, but mainly in the distal section, which was where the fewest spurs
formed. So, even if the distal section of the shoot appears more productive, this is not the
case, since the more sustainable fruiting occurs in the medial and proximal sections.

Knowing the location of spurs and the spurs ﬂowering characteristics could be

helpful in managing the tree. The one variable not measured that may be useful for

84

future work is the evolution of the branch, or how spurs within a branch age. Branch
evolution in this trial may be implied since tree habit tends to repeat itself, such that one-
year-old shoots may repeat pattern of the shoots in this trial (Tomlinson, 1983). Spur
evolution, however, is something that we cannot predict from this trial. Whether the
spurs will continue to produce the same number of buds and ﬂowers, and at what point
these spurs will change the number of buds and/or ﬂowers they produce, is not yet
known. A second question arises as to whether the same amount of ﬂowering will occur
in the one-year-old shoots, causing the same relative amount of blind node production in
the succeeding years. We did not look at the way that the metamer types and quality
change in these shoot sections over time. This is a major factor in tree management,
though, since rootstock may also affect how well the spurs age.

This effect of rootstock on location of different metamer types, independent of the
rootstock effect on tree size, implies a need to more accurately assess tree growth habit in
tart cherry. Lespinasse and Lauri (1996) have noted that prediction of the distribution of
speciﬁc metamers is one the three variables that must be understood before an accurate
prediction and assessment of the tree’s productive potential can be found. This is
currently a critical step in the evaluation and adaptation of new precocious and/or size-

controlling rootstocks for tart cherry production.

85

LITERATURE CITED

Cowgill, W. and J. Clements. 2002. NC-140 regional rootstock research project. NC-
140. <http://www.nc140.org > 23 September 2002.

Crabbe, J .J . 1984. Vegetative vigor control over location and fate of ﬂower buds in ﬁ'uit
trees. Acta Horticulturae 149: 55-63.

Diaz, D.H., H.P. Rasmussen, and F.G. Dennis, Jr. 1981. Scanning electron microscope
examination of ﬂower bud differentiation in sour cherry. Journal American Society of
Horticultural Science 106: 5 13-5 15.

Franken-Bembenek, S. and W. Gruppe. 1985. Effect of different hybrid rootstocks on
growth and yielding characters of sweet cherries. Acta Horticulturae 169: 219-226.

Lang, GA. 2000. Precocious, dwarﬁng, and productive — how will new cherry
rootstocks impact the sweet cherry industry? HortTechnology 10: 719 — 725.

Lespinasse, J .M. and PE. Lauri. 1996. Inﬂuence of fruiting habit on the pruning and
training of apple trees. Compact Fruit Tree 29: 75-82.

Nugent, J .E. “Training Tart Cherry Trees.” Northwest Michigan Horticultural
Experiment Station. <http://www.maes.msu.edu/nwihort> (16 April 2001).

Perry, R..l996. Performance of Montrnorency on 25 rootstocks in the NC-14O cherry
trial at the Northwest Horticultural Research Station. Annual Report. Michigan
Horticultural Society, 126: 126-129.

SAS Institute. 1989. SAS/STAT User’s Guide, Version 6. (SAS Institute, Cary, NC).

Schaumberg, G. and W. Gruppe. 1985. Growth and fruiting habit of Prunus avium cv.
‘Hedelﬁnger’ on clonal cherry hybrid rootstocks. Acta Horticulturae 169: 227-234.

Schultz, EA. and G.W. Haughn. 1991. LEAF Y, a homeotic gene that regulates
inﬂorescence development in Arabidopsis. Plant Cell 3: 7 71-781.

Thompson, M. 1996. Flowering, Pollination, and Fruit Set. In Cherries: Crop
Physiology, Production, and Uses. A.D. Webster and NE. Looney, Eds. CAB
International, Wallingford, UK, pp. 223-242.

Tomlinson, PB. 1983. Tree Architecture. American Scientist 71: 141-149.
Westwood, MN. and AN. Roberts. 1970. The relationship between trunk cross-

sectional area and weight of apple trees. Journal of the American Society of Horticultural
Science 95(1): 28-30.

86

White, J. 1984. Plant metamerism. In Perspectives in plant population ecology. Dirzo,
R. and J. Sarukhan, eds. Sinamar Associates Incorporated, Sunderland, MA. pp. 15-47.

Wustenberghs, H. and J. Keulemans. 2000. Groenprincipen en groenmanipulatie bij
steenfruit. Katholieke Universiteit Leuven, Brussels, 198 pp.

87

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APPENDIX B

137

LEAF Y project:

1. Rationale

1.1 History

 

The idea behind this project was to ﬁnd a gene that could be involved in the early

stages of ﬂower induction in sweet cherry.

 

The LEAF Y (LFY) gene of Arabidopsis thaliana is a well-conserved gene in many
plant species, including gymnosperms and angiosperrns, and appears to be involved

in the transition to ﬂowering (see section 1.2)

1.2 LEAFY gene

The LP Y gene and its activity has been one of the most promising genes for
increasing precocity as well as ﬂower density in trees (Egea—Cortines and Weiss,
2001). LF Y is well-conserved, and its homologues have been found in many diverse
species. The location of LF Y was found to be on chromosome 5 of Arabidopsis
(Schulz and Haughn, 1991). Mellerowicz et a1. (1998) showed that, although LFY
homologues are found in pre-angiosperm species, some differences exist in their
sequences and, subsequently, proteins. The proline-rich and acidic domains in LFY

and FLORICAULA (FLO) [the snapdragon (Antirrhinum spp.) homologue of LFY],

138

whose presence indicates that they are transcription factors, are not evident in
conifers. However, the C-terminal part of the protein, whose function is not yet
known, is highly conserved between conifers and angiosperrns (Mellerowicz et al.,
1998). Blazquez et a1. (1997) demonstrate that LF Y is both necessary and sufﬁcient
for the initiation of individual ﬂowers. LF Y expression and ﬂower formation are not

strictly coupled, because LFY expression in the wild-type Arabidopsis precedes

 

ﬂower formation (Blazquez et al., 1997). However, upregulation of the LFY
promoter appears to be an indicator of subsequent ﬂowering, because failure to

ﬂower in short days in the GA-deﬁcient gal-3 mutant goes hand in hand with the

 

elimination of LF Y upregulation (Blazquez et al., 1998). LFY also appears to
suppress leaf development (Weigel et al., 1992; Weigel and Meyerowitz, 1993). LF Y
is of primary importance in the transition ﬁ'om the vegetative to reproductive phase of
meristems: lfy mutants of Arabidopsis have leaves in the locations where the ﬁrst
ﬂowers form and later-arising ﬂowers are replaced by structures with partial shoot
characteristics (Blazquez et al., 1997). In 115» mutants, normal ﬂowers are never
produced. Instead of ﬂowers, 1ij mutant shoots resemble lateral shoots in that they
produce an indeterminate number of metamers with elongated internodes, bract-like
organs, tertiary lateral shoots, and spiral phyllotaxy (Schultz and Haughn, 1991).
Blazquez et al. (1997) also observed that LFY is expressed in lateral primordia
continuously from the vegetative to reproductive phase, changing only in intensity.
Quantitative increases in LF Y expression to a threshold level are a major factor in the
transition to ﬂowering (Blazquez et al., 1998). Blazquez et al. (1997) suggest that

LFY is expressed in emerging leaf primordia because this is where ﬂoral induction is

139

effective, as these primordia have the ability to make the transition to become ﬂoral
once LF Y activity reaches a critical level.

When transformed into other species, LF Y still speciﬁes a ﬂoral fate. Wei gel
and Nilsson (1995) have demonstrated that in aspen, a perennial tree, LF Y is
sufﬁcient to determine ﬂoral fate in lateral meristems and increase precocity. When

transformed into aspen, LF Y was sufﬁcient to trigger ﬂower initiation. Aspen

 

normally ﬂowers after 8 years, but transgenic LF Y aspen ﬂowered within just a few

months of germination (Coupland, 1995). Constitutive expression of LF Y in aspen ;

 

results in solitary ﬂowers being produced in the axils of normal leaves, as well as the

 

number of vegetative leaves being limited, the shoot apical meristem being turned
prematurely into a terminal ﬂower, and precocious ﬂower development (Weigel and
Nilsson, 1995). In citrus, the juvenile phase normally lasts from 6 to 20 years, but in
both LFY and API transgenic citrus trees ﬂowers were initiated in the ﬁrst year (Pena
et al, 2001). In both cases, trees ﬂowered in consecutive years, as well as under the
control of environmental signals, and LFY and API expression were found in the
leaves. The LFY transgenic lines, compared to the controls, had a weeping growth
habit and thin stems, reduced leaf size and a curling of the leaves. Citrus ﬂower buds
normally give rise to a range of inﬂorescence types, including solitary ﬂowers to
mixed ﬂowers to leaf racemes, and all of these inﬂorescence types were found in the
transgenic LF Y citrus lines. Transgenic APl trees on the other hand had a more
normal growth habit than the transgenic LFY lines O’ena et al., 2001).

LFY homologues and LFY-like genes have been identiﬁed and cloned in a

diverse range of plant species (Weigel and Nilsson, 1995). Although LFY is well-

140

conserved, its role in transition to ﬂowering is not very conserved. Overexpression of
PTLF, the homologue of LF Y in Populus trichocarpa (poplar), resulted in no early
ﬂowering phenotype or other differences as compared to the control trees, even
though when PT LF was transformed into Arabidopsis, it caused ﬂowering to occur 5
days earlier than the control (Rottrnann et al., 2000). Even without the early-
ﬂowering phenotype of PTLF in poplar, the strongest PTLF expression was in the
lateral ﬂoral meristems. F LORICAULA (FLO), the LF Y homologue in Antirrhinum .1
majus, shares 70% amino acid identity. Both LFY and FLO are expressed in the

ﬂoral meristem prior to initiation of ﬂoral organ primordial, while expression at later

 

stages of ﬂoral development is less conserved (Coen et al., 1990; Weigel et al., 1992). 4
The LP Y homologue cloned in Pinus radiata, PRFLL, shares 53% similarity with
LFY (Mellerowicz, 1998). Expression of PRFLL was found in vegetative buds of
juvenile, adolescent, and mature trees, but not in vascular carnbium, roots or
secondary needles. PRFLL mRN A was detected in buds [in which cone and shoot
primordia will develop] and in developing male cones, but not in developing female
cones. Expression was particularly high in buds of the axillary meristems prior to
their differentiation as male cones, which is consistent with PRF LL being involved in
determination of male cone primordia. (Mellerowicz et al., 1998). Southerton et a1.
(1998) have isolated 3 LF Y homologue, ELF, in Eucalyptus (Eucalyptus L ’Her. spp.)
whose sequence and expression pattern in ﬂoral primordia is very similar to LFY and
FLO. A LF Y homologue, LtLFY, has also been found in the grass species Lolium
tementulum (Gocal et al., 2001). LtLFY has only 56% amino acid identity with LFY.

Like the other LF Y homologues, the C-terminal region of LtLFY is more highly

141

conserved than the amino-terminal region. In Lolium tementulum, APl homologue
expression precedes LtLF Y expression, implying that the regulatory pathway of ﬂoral

initiation may not be well-conserved in monocots (Gocal et al., 2001).
1.3 Brief overview
The idea behind this project was to isolate a gene in sweet cherry that had homology n

to the Arabidopsis LFY gene, and to see if it was upregulated during the ﬂower

initiation period in ﬂoral buds. As an addition to this experiment, we also looked at f,

 

"I' a. ;

the same sweet cherry scion cultivar (‘Hedelﬁnger’) on two different rootstocks: a
vigorous rootstock with little to no ﬂowering (‘Mazzard’), and a nonvigorous
rootstock that has already begun to ﬂower (‘Gisela 6’) to see if upregulation of LF Y

occurred in both of these rootstock/scion combinations similarly or differently.

2. Materials and Methods

2. 1 Plant materials

Sweet cherry (Prunus avium L.) ‘Hedelﬁnger’ trees grafted on Gisela 6 (Gi.6) and

Mazzard rootstocks were used in this study. Trees were four years old and located at

the Michigan State University’s Northwest Michigan Horticulture Research Station

near Traverse City, Michigan.

142

 

2.2 Plant tissue collection

Buds were collected from one-year-old shoots of ‘Hedelﬁnger’ trees on Gi.6 and
Mazzard. Seven buds from each of eight trees on Gi.6 and eight buds from each of
seven trees on Mazzard were collected on the following dates and stored at —80° C
until RNA was extracted:

17 May 2001

5 June 2001

22 June 2001

4 July 2001

17 July 2001

14 August 2001

 

‘Hedelﬁnger’ buds were collected in mid-March 2002 (these were used to prime for

the conserved regions of LFY)

Young leaves, sepals, petals, and ﬂoral buds were collected in spring 2002 for use as

controls.

2.3 RNA extraction

Total RNA was isolated from ‘Hedelﬁnger’ buds and leaves using a method based on
hot borate and proteinase K adapted ﬁ'om Hunter and Reid (2001). Approximately 1
gram of frozen tissue was ground into a ﬁne powder. Crushed tissue was added to

hot borate buffer (0.2 M soditun borate decahydrate, 30 mM EGTA, 1% (w/v) SDS,

143

 

1% (w/v) sodium deoxycholate, at 80° C) and vortexed for 30 s in a 14 mL Falcon
2059 tube. Proteinase K (37.5 uL of 0.75mg per 5 mL) was added to the tube and
incubated horizontally on a shaking air incubator for 1.5 h at 42° C. 0.08 volumes of
2 M KCl was added and tubes were incubated horizontally on ice with shaking for 30
min. Tubes were centriﬁiged at 12,000 rpm for 20 min at 4° C, and supernatant was
decanted into new sterile 2059 Falcon tubes. One volume of 4 M LiCl was added and
tubes were incubated overnight at 4° C. RNA pellet was precipitated by centrifuging
at 12,000 rpm for 30 min. at 4° C. Pellet was resuspended in 630uL HzO/70 uL of
3M sodium acetate, precipitated with 1 volume of isopropanol, and pelleted by
centrifugation at 16,000 x g for 30 min at 4°C. RNA pellet was washed with 70%
ethanol, resuspended in 100 uL double-distilled RNase-free H20, and stored at -20°C.

One gram of frozen tissue produced 25.4 pg of RNA at 25.4 ug/uL.

2.4 RT -PCR

First strand cDNA synthesis of total RNA from 1 gram of bud samples (2. 2) was
performed using SUPERSCRIPTTM Reverse Transcriptase according to protocol 0.
RNase was added to resultant cDNA mix to a ﬁnal concentration of 10 ng/ uL, and
solution was incubated at 37° C for 10 min. cDNA was puriﬁed using QIAquick®
PCR Puriﬁcation Kit (Qiagen, 2001), and eluted in 40 uL buffer EB(10mM Tris-Cl,
pH 8.5). This was used as a template to amplify the conserved 763 bp fragment of

Arabidpsis thaliana LF Y homologue cDNA. Primer sequences were: 5'- ATG AAR

144

 

 

 

GAY GAD GAR MTY GAN GA -3' and 5'- BCA RAG CTG RCG NAR YTT NGT

KGG MAC RTA CCA AAT -3'.

PCR protocol: 0.1 pL cDNA, 0.5 dNTPs, 0.5 uL pol, 2.5 uL buffer, and H20 to
25 uL was gently mixed and PCR was done as follows: 2 min at 94° C, 25 x (30 sec
at 94° C; then 2 min 30 sec at 68° C), 2 min 30 sec at 68° C. These were

electophoresed through 2% agarose. n

 

2.5 Southern analysis U

A southern analysis was performed according to a protocol based on Church and
Gilbert (1984). The gel (see 2.4) was blotted onto a nylon membrane. Figure A-l
shows, with an arrow, the 923 bp fragment. Arabidopsis LFY probe was denatured,
labeled with radioactive phosphorous, and hybridized to blots overnight (> 8h) at
55°C in hybridization buffer (lmM EDTA pH 8.0, 250 mM NazHPO4(7HzO),
7%SDS, adjusted to pH 7.4 with H3PO4). Blots were rinsed twice in the wash

solution (lmM EDTA pH 8.0, 40 mM Nal-IPO4, 1% SDS) for 30 min at 55°C.

2. 6 Ligations
The 923 bp band was extracted from the 2% agarose gel using QIAquick® Gel

Extraction Kit (Qiagen, 2001), and eluted in 50 uL Buffer EB. Ligations were done

using the pGEM-T and easy vectors and the 2X Rapid Ligation Buffer (in each tube,

145

 

 

 

mix 5 uL 2X Rapid Ligation Buffer, l uL pGEMT Easy Vector, 1 uL T4 DNA
Ligase, deionized water to a ﬁnal volume of 10 uL, and either 3 uL of the 923 bp
band, or the positive control, or the negative control. Tubes were incubated overnight
at 4° C). 3 uL of ligations were mixed with 1 mL LB and competent cells, and then
they were zapped with voltage. Cells were grown for 1 hour at 37°C on a shaker.
These were then centriﬁrged in 1 mL tubes a few times. Supernatant was taken off,
and ~ 100 uL of solution plus cells was left. The cells were resuspended with a
pipette, and spread on a LB/carbenicillan/X-Gal plates. Plates were stored at 37°C

upside down.

Two white patches were collected from the plate. These 2 single well-isolated
colonies were collected into tubes with 3 mL LB culture medium and 3uL
carbenicillin 100. These tubes were incubated overnight at 37°C in a shaking

incubator. A cleared lysate was produced from these colonies, and DNA was isolated

and puriﬁed according to Promega.

DNA was digested with EcoRI enzyme (200 ng DNA, 2 uL EcoRI 10X buffer, 0.25
uL EcoRI, 1 uL BSA, H2O to 20p.L at 37°C for 1 hour). These were

electrophoresced through 2% agarose.

Sequencing was done at the Genomics Technology Support Facility (Michigan State

University; http://www.genomics.msu.edu).

146

 

2. 7 Northern Analysis

A northern analysis was performed according to a protocol based on Church and
Gilbert (1984). The gel was blotted onto a nylon membrane. The sequenced 923 bp
region was used as a probe, and was denatured, labeled with radioactive phosphorous,
and hybridized to blots overnight (> 8h) at 55°C in hybridization buffer (lmM EDTA
pH 8.0, 250 mM Na2HP04(7H20), 7%SDS, adjusted to pH 7.4 with H3PO4). Blots
were rinsed twice in the wash solution (lmM EDTA pH 8.0, 40 mM Nal-IPO4, 1%

SDS) for 30 min at 55°C.

 

3.1 Results

3.1 Identiﬁcation of 0 LF Y homolog

Primers for LP Y were made in areas that were well-conserved in many species and

used to prime sweet cherry cDNA. Table B-1 shows sequence obtained that has 86%

identity with Malus x domestica AF L2, the apple LF Y homolog.

147

Table B-1: Sequence of 923 bp region (see section 2-6 and 2-7) used as a probe for
the northern analysis. Sequence shows 86% identity with Malus x domestica AFL2
mRNA.

Sequence:

gacatgatgagtagcctctctcagatattcaggtgggatttgcttgtgggtgagaggtacggtatcaaagcggccgtcagagcag
agcgtcgccgcctcgatgaccaggactcgaggcgccgcccc . . . gtctccggcgacaccaccaccaatgccctagatgctctc
tcccaagaagggttgtcagaggagccggtgcaacaagagaaggagatggtggggaccggcggaggggccgcgtgggaag

tggtggcgtctgcaggggagaagcggaagaagcagcgaaggacgaaaaatgggcaatataggaattttaatggcatcggaag
ggggcataataataatgatcataatgagggtgtggacgacgaggacgacaacgacatggacgatatgaatgggcacgggaac

ggtggaggaggggggttgccgagcgagagagtgagggagcacccgttcattgtgactgatcctgaggaggtggcacgtggc

aaaaagaacggcctagattacctcttccatctctacgagcagtgccgtgatttcttgatccaggtccaaaacattgcagaggagcg
cggtgaaaaatgtccaaccgaggtaacaaaccaagtgtgtatgtttgccaaaaaggcanggggcagctacatcaacaagccaa
aaatgcgacacta

 

 

148

Figure B-l: Southern blot (see section 2-5). Arrow shows the 763 bp fragment.

 

149

 

 

 

Figure B-2: Northern Analysis (see section 2-7) of bud samples collected during
2002 (see section 2-2). Arrow shows the Gisela 6, August 14"' 923 hp band, which
was the only one observed in the northern analysis.

   

150

Blazquez, M.A., L.N. Soowal, 1. Lee, and D. Weigel. 1997.LEAF Y expression and
ﬂower initiation in Arabidopsis. Development 124: 3835-3844.

Blazquez, M.A., R. Green, O.Nilsson, M.R. Sussman, and D. Weigel. 1998. Gibberellins
promote ﬂowering of Arabidopsis by activating the LEAP Y promoter. Plant Cell 10:
791-800.

Coen, E.S., J .M. Romero, R. Elliot, G. Murphy, R. Carpenter. 1990. FLORICAULA: a
homeotic gene required for ﬂower development in Antirhinum majus. Cell 63: 1311-
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