llHl‘lHHlWllH!WWIHUNHIWIHHIHHI

  

  

IH-h‘
Iooo
lcnooou

ll}\lllllllljllflllllllfllfllllllllfllllfll mu"

Michigan State
University

 

This is to certify that the

thesis entitled

DEVELOPMENT OF THE INFLORESCENCE IN 'MONTMORENCY'
SOUR CHERRY (PRUNUS CERASUS L.) AND EFFECTS OF
COMPETITION—EETWEEN'TND WITHIN FLOWER
CLUSTERS ON FRUIT SET AND ABSCISSION

presented by
Daniel Humberto Diaz

has been accepted towards fulfillment
of the requirements for

Ph. D. degree in We

 

J2 Jj/Qm

Major professor

Date A/LZLCWJ44, £23] [9178

0-7639

 

OVERDUE FINES ARE 25¢ PER DAY
PER ITEM

Return to book drop to remove
this checkout from your record.

Ry
SE. 0%”

 

 

 

 

 

DEVELOPMENT OF THE INFLORESCENCE IN 'MONTMORENCY'
SOUR CHERRY (PRUNUS CERASUS L.) AND EFFECTS OF
COMPETITION BETWEEN AND WITHIN FLOWER
CLUSTERS ON FRUIT SET AND ABSCISSION

 

BY

Daniel Humberto Diaz

A DISSERTATION

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

DOCTOR OF PHILOSOPHY

Department of Horticulture

1979

ABSTRACT

DEVELOPMENT OF THE INFLORESCENCE IN 'MONTMORENCY'
SOUR CHERRY (PRUNUS CERASUS L.) AND EFFECTS OF
COMPETITION BETWEEN AND WITHIN FLOWER
CLUSTERS ON FRUIT SET AND ABSCISSION

BY
Daniel Humberto Diaz

Field plots were established in a commercial
Michigan sour cherry orchard to investigate some of the
factors which might affect fruit set, including competition
among flowers and fruits, nitrogen applications and growth
regulators. Flower differentiation was also monitored
using scanning electron microscopy.

No correlation could be established between percent
of sour cherry pistils killed by freezes and percent set of
the surviving flowers. Reduced flower density following
freeze injury was associated with reduced fruit set.
Regardless of flower density approximately 25% of the
flowers which survived freezes yielded mature fruit. Hand
removal of two-thirds of the flower buds at bud swell did
not alter percent set significantly. Competition between
flower clusters is therefore not a factor controlling fruit
set. Removal of two-thirds of the flower buds for two or

three consecutive years did not affect set as compared to

Daniel Humberto Diaz

control; thus fruit load does not appear to affect subse-
quent percent fruit set. Abscission of flowers and immature
fruits was not affected by flower bud thinning at bud swell
or by removal of two-thirds of the fruits or leaves 2 weeks
after bloom.

Within clusters fruit set of flowers that opened
early was greater (25-36%) than that of flowers which
opened late (19-27%). This was not affected by selective
hand removal of flowers within clusters; thus fruit set is
not affected by competition among flowers within clusters.
Within flower buds tetrad formation in anthers of flowers
which opened early occurred 1-2 days earlier than in those
which opened late, and embryo sacs in the early opening
flowers were less subject to degeneration than were those
in the late-opening flowers.

Critical point dried axillary buds of 'Montmorency'
sour cherry were viewed in the scanning electron microscope
to determine the morphological changes which occur during
flower formation. The first evidence of change from the
vegetative to the reproductive stage occurred as a flatten-
ing of the apex five weeks after full bloom. Sepal
primordia were evident 45 days after the first signs of
initiation and 2 weeks later petal and stamen primordia
developed. Pistil initiation occurred about 3-4 weeks
later. Up to the time of anther and probably pistil

initiation, flowers within a bud differ in stages of

Daniel Humberto Diaz

development and these differences probably play a role in

the setting potential of such flowers.

To my parents, Raul and Celia, for

their love and encouragement

ii

ACKNOWLEDGMENTS

I wish to express sincere thanks and gratitude to
Dr. Frank G. Dennis for his careful guidance and encourage-
ment throughout my research and graduate studies, and to
Drs. Martin J. Bukovac, Robert L. Andersen, Jerome Hull
and Alan Jones for their suggestions and support.

Appreciation is due to Mr. Rudolph Fuehring for the
use of his orchard.

I am grateful to Mr. Vivion Shull and Dr. H. Paul
Rasmussen for their assistance during my photographic and
scanning electron microscope work, to Doug Archbold for
his help in the field, to all fellow Horticulture graduate
students and to my friends for their sincere companionship
during my studies.

A special word of appreciation to my wife, Irma,
for her sacrifices, understanding and encouragement during
the time of this study. To my son, Daniel Jr., thanks for
his unsuspected sacrifices and wonderful times spent
together.

Lastly I wish to acknowledge the financial support
granted me by the Consejo Nacional de Ciencia y Tecnologia
of Mexico, and especially to the Colegio de Postgraduados in

Chapingo for its continuous encouragement.

iii

TABLE OF CONTENTS

LIST OF TABLES . . . . . . . . . . . . .

LIST OF FIGURES. . . . . . . . . . . . .

INTRODUCTION. . . . . . . . . . . . . .

LITERATURE REVIEW . . . . . . . . . . . .

Sour Cherry Production. . . . . . . . . .
Origin of 'Montmorency' . . . . . . . . .
Flower Bud Formation . . . . . . . . .

Fruit Set and Abscission of Fruits. . . . . .
Internal Factors Affecting Fruit Set . . . . .
External Factors Affecting Fruit Set . . . . .
Summary. . . . . . . . . . . . . . .
Literature Cited. . . . . . . . . . . .

SECTION I

EFFECT OF FLOWER AND FRUIT DENSITY ON FRUIT
SET AND ABSCISSION OF SOUR CHERRY (PRUNUS
CERASUS L. CV. MONTMORENCY)

Abstract . . . . . . . . . . . . . .
Materials and Methods . . . . . . . . . .
Results and Discussion. . . . . . . . . .
Literature Cited. . . . . . . . . . . .

SECTION II
SCANNING ELECTRON MICROSCOPE OBSERVATIONS OF

FLOWER BUD DIFFERENTIATION IN SOUR CHERRY
(PRUNUS CERASUS L. CV. MONTMORENCY)

 

Abstract . . . . .

Materials and Methods . . . . . . . . . .
Results and Discussion. . . . . . . . . .
Literature Cited. . . . . . . . . . . .

iv

Page
vi

viii

26
28
34
48

50

52
59

APPENDICES Page

Appendix A--Predicting Persistence of Sour Cherry
Fruits by Ovary Diameter. . . . . . 60

Appendix B--Effect of Numbers of Tree and Limb
Replicates and of Number of Buds per
Limb on Variability of Data for Fruit
Set of Sour Cherry. . . . . . . . 66

Appendix C--Effect of Nitrogen Fertilization on
Vegetative and Reproductive Characters
of Sour Cherry (Prunus Cerasus L.) . . 72

 

Appendix D--Growth Regulators and Fruit Set of Sour
Cherry (Prunus Cerasus L.) . . . . . 76

 

LIST OF TABLES

Table Page
SECTION I

1. Experimental Arrangement of Treatments to
Evaluate the Effects of Flower and Fruit
Density and Defoliation Within Limbs on
Fruit Set. . . . . . . . . . . . . 30

2. Effect of Removal of Two-Thirds of the
Flower Buds Before Bloom, or Two—Thirds of
the Fruits or Leaves 2 Weeks After Bloom on
Subsequent Percentage Fruit Set of 'Mont-
morency' Sour Cherry. Data Corrected for
Freeze Injury. One Limb on Each of 4 Trees
per Treatment . . . . . . . . . . . 37

3. Classification of Flower Clusters by Fruiting
Performance According to Sequence of Flower
Opening . . . . . . . . . . . . . 44

4. Effect of Flower Removal Within Clusters upon
Set of Remaining Flowers. . . . . . . . 45

5. Effect of Flower Position on Egg Cell
Normality, 1978. . . . . . . . . . . 47

APPENDICES

A-l. Abscission Date and Percent Set at Harvest
of 'Montmorency' Sour Cherry Fruits in
Relation to Ovary Diameter 13 Days AFB,
1977 . . . . . . . . . . . . . . 64

3-1. The Effects of Number of Trees and Limbs per
Tree on the Estimated Variance of the
Sample Mean (82?) for Percenta e Fruit

Set in a Population in which S = 53.16
and s; = 13.45, with 1 to 10 Tfees per

Replication, 1978 . . . . . . . . . . 69

vi

Page

Effect of the Number of Flower Buds per Limb
on the Coefficient of Variation (%) of
Fruit Set Data, 1978. . . . . . . . . 70

Vegetative, Flowering, and Fruiting Responses
of 9-Year-Old 'Montmorency' Sour Cherry
Trees to 3 Levels of Nitrogen, 1977. . . . 74

Effects of Growth Regulators Applied in 1977
on Fruit Set of 'Montmorency' Sour Cherry
in 1977 (Experiments I and II) or 1978
(Experiments III and IV) . . . . . . . 79

vii

Figure

LIST OF FIGURES

SECTION I

Differential opening of flowers within a
cluster . . . . . . . . . . . . .

Freeze injury to flowers versus fruit set
at harvest in 'Montmorency' sour cherry,
1977 and 1978 . . . . . . . . . . .

Effect of flower bud thinning on flower
and fruit drop pattern, 1976 (A) and
1977 (B). Data based on number of per-
sisting fruits. . . . . . . . . . .

Daily absolute fruit drop for 'Montmorency'
sour cherry, 1977. Data based on number
of falling fruits. . . . . . . . .

SECTION II

Scanning electron micrographs of critical
point dried apices of sour cherry (Prunus
cerasus L. cv. 'Montmorency') showing
developmental changes during flower
initiation. A. Initial phase of change
from vegetative to reproductive stage by
rounding of the apex, with bract primor-
dium (BP), June 10. x 600. B. Flattening
of the apex, June 15. x440. C. Floral
primordia (FP) developing in the axil of
each bract primordium, June 28. x510.

D. Floral primordia evident in 3 bracts

and a 4th beginning to form, June 30.

x410. E. Ovate stage of flower primordia,
July 3. x320. F. Round stage of flower
primordia, July 10. x300 . . . . . . .

viii

Page

32

36

4O

43

54

Figure Page

2. Scanning electron micrographs of critical
point dried apices of sour cherry (Prunus
cerasus L. cv. 'Montmorency') showing
developmental changes during flower differ-
entiation. A. All apex space occupied by
three floral primordia, July 20. x410.

B. Calyx evident as sepal primordia (SP)

in a pentagonal whorl, July 30. x300.

C. Corolla and stamens evident as petal

primordia develop within sepal primordia,

August 15. x165. D. Stamen primordia

developing below petal primordia (PP),

August 15. x400. E. Pistil initial (PI)

arising from flat apex, September 10.

x360. F. All floral organs present,

September 29. x150. . . . . . . . . 57

APPENDICES

A-l. Growth curves for groups of persisting and
abscising fruits, 1977. . . . . . . . 63

ix

Guidance Committee:

The journal-article format was adopted for this
dissertation in accordance with departmental and university
requirements. Two sections were prepared and styled for
publication in the Journal of the American Society for

Horticultural Science.

 

INTRODUCTION

Michigan produces about 60-70% of the national
tonnage of sour cherries. Almost the entire crOp is frozen
or canned, and one cultivar, 'Montmorency', accounts for
all but a few tons.

One of the most important problems of the cherry
industry is fluctuating yearly yields, caused primarily by
spring frosts which kill some of the flowers. Also, the
shedding of flowers or immature fruits is so heavy in some
years that the crop is greatly reduced.

To avoid freeze injury, attempts have been made to
delay bloom of fruit trees using either growth regulators
(14, 41) or evaporative cooling (8, 51, 57). Response to
growth regulators has not been encouraging and side effects
make their use questionable (14). Evaporative cooling is
more effective in arid (1) than in humid (Dennis, personal
communication) regions, delays of up to 2 to 3 weeks having
been achieved under arid conditions as compared to 6 to 7
days in humid areas.

For many years researchers have tried to establish
what controls fruit set and abscission in order to be able

to manipulate production. If this were possible, one might

compensate for moderate frost injury by increasing the per-
centage set of the remaining flowers. Many factors control
fruit set and abscission, and most appear to be critical

at one or more stages of development. For sour cherry,
competition between individual blossoms or fruits (3, 4),
and early embryo sac degeneration (4, 37) may reduce fruit
set.

The objectives in this research were (a) to deter-
mine the effect of position of flowers within the cluster
on egg cell normality: and the effects of flower position
and density on fruit set and abscission, and (b) to
describe the morphological and anatomical development of
the flowers from initiation in early summer until just

prior to bud swell the following spring.

LITERATURE REVIEW

Sour Cherry Production

 

Michigan ranks first among the United States in
production of sour cherry. Within the state in 1977, an
average year, sour cherries accounted for 22% of the
acreage, 20% of the total production and 39% of the total
value of fruit crops (55). Within the last 10 years the
total production of sour cherries in the United States has
varied between 90 and 220 million pounds, mainly because
of fluctuations in yield in Michigan. These fluctuations
have caused the same effects on price of cherries to the
producers with a range of 15 to 50 cents per pound with
consequent major problems in marketing. By 1985 sour
cherry production in Michigan is expected to be 224 million
pounds, or 39% above the average for 1973-1978 (46).
Observers (46) predict an 8% increase in acreage plus an
increase in yield per acre. The industry must find a way
to reduce fluctuations in production from year to year in
order to maintain a uniform market that would economically

benefit growers.

Origin of 'Montmorency'

 

The cultivar Montmorency accounts for most of the

sour cherry production. It is believed to have originated

3

in the Montmorency Valley in France around the seventeenth
century, probably as a seedling of 'Cerise Hative' or
'Cerise Commune'. It was first mentioned by Duhamel in

1768 and in America in 1832 by William Prince (40).

Flower Bud Formation

 

In most deciduous fruit trees, flowers are initiated
and differentiate the summer before they open. Goff (32)
in 1899 was the first to report on the origin and develop-
ment of flowers in stone and pome fruits. Other workers
have provided additional information (20, 33, 36, 76).
Depending on the location, condition of the tree and the
cultivar under study, initiation (visual morphological
change in apex) occurs in sour cherry about 5 to 6 weeks
after full bloom and differentiation of most flower parts
is complete 8 to 10 weeks later. The first noticeable
change in the apex is a flattening-out. As the season
progresses the apex becomes concave, and sepal, petal and
stamen primordia develop acropetally (36). Gibberellin
inhibits flower differentiation in peach (9) and cherry
(10, 45), while SADH hastens it (58). Fully developed
reproductive buds contain 2 to 4 flowers in an inflores-
cence that Goff (32) classified as a corymb. He noted that
the proximal flower was slightly more advanced than the

others.

Fruit Set and Abscission

of Fruits

 

 

Deciduous fruit species normally produce many more
flowers than will set fruit. Continuous shedding of flowers
shortly after bloom and of immature fruits throughout the
fruit maturity season results in a low percentage of flowers
developing into mature fruits. Peach normally sets 30% of
its flowers (38), almond, 30% (48), and sour cherry, 25%
(4). As important as knowing what percentage of flowers
will produce mature fruits is knowing what percentage must
set in order to yield a commercial crop. Fletcher (25)
reported that for plum and apricot a 13% set assured a good
crop when no frost occurred, while Roberts reported 25% for
sour cherry (68).

The abscission patterns of flowers and immature
fruits have been established for most of the stone fruits.
Those of the peach (16, 38, 90), almond (48), plum (17) and
sour cherry (3, 37) are very similar. Three periods of
fruit drop occur; the first takes place during bloom or
shortly thereafter and appears to consist largely of defec-
tive flowers which drop without appreciable enlargement
of the ovary. Their pedicels are often shorter than normal
and the style and calyx cup do not abscise (4, 38, 48).

The time of the second drop varies with species, occurring
about a month after bloom in almond and peach (2, 38, 48).
and about a week after the end of the first drop in sour

Cherry (3, 37). Sour cherry fruits falling in this drop

6

are primarily 5-7 mm long. The calyx cup and style have
abscised and the ovary is slightly yellow and has a dull
surface appearance in comparison with developing fruits
(4). The third drop occurs about three weeks after the
second in sour cherry (3, 37) and about six to seven weeks
after full bloom in almond and peach (38, 48). The fruits
in this drop are large (9-10 mm long) with an ovate shape
as compared to the globoid shape of persisting fruits

(4, 38, 48).

The prOportion of fruits which fail to develop to
maturity varies from year to year. A range of 50 to 75
percent drop of the total number of blossoms has been
reported for sour cherry in various years (4). Distribution
of the drops also varies among years. In almond no first
drop occurred one year (48), while in sour cherry an inverse
relationship often exists between the intensities of the
first and second drops (4, 37). The proportion of fruits
falling in the third drop is generally low relative to the

total number of abscising fruits.

Internal Factors Affecting
Fruit Set

 

 

a) Compatibility. Some tree fruit cultivars are

 

receptive to their own pollen (self-compatible), some are
not (self-incompatible). In the latter pollen must be
supplied by another cultivar (cross-pollination). Most
apple and pear cultivars require cross-pollination while
most peach cultivars are self-compatible. Most of the self-

incompatible peach cultivars have been eliminated from the

market because of their need for interplanting and insect
pollination (54). Most sweet cherry cultivars are self-
incompatible. Three of the most important cultivars--Bing,
Lambert, and Napoleon--are inter-incompatible (27, 81), and
therefore interplanting is essential. The need for insect
pollinators is especially important for any species in
which some cultivars are self-incompatible.

Some sour cherry cultivars are reportedly both self-
and inter-compatible (4, 89) but others are self-
incompatible (61). Roberts (67) stated that blossoms of
'Montmorency' were self-compatible and that insect pollina-
tors were not needed. Marshall et a1. (52) found that
hand pollination with 'Montmorency' pollen increased set
of 'Montmorency' (24%) in comparison with open pollinated
flowers (7.5%). Similar results were reported by Hootman
(42), Shoemaker (71) and Wocior (87).

Fruit set of 'Montmorency' trees which were caged
with bees was 31% in comparison with 11% for the controls
(71). Similar results have been reported by Drescher (19).
Roberts (67) observed that the use of other cultivars,
such as 'Early Richmond', as a source of pollen increased
set of 'Montmorency'. Marshall et a1. (52) confirmed this
and suggested that higher viability of 'Early Richmond'
pollen might be responsible for the difference.

Therefore, although most of the sour cherry culti-
vars are self-fruitful, insect pollination seems to be

essential and cross-pollination may be beneficial.

Wocior (88) collected pollen from sour cherry
flowers opening before, after, or at full bloom; maximum
germination and tube growth occurred in that collected at
full bloom.

b) Pollination, fertilization and embryo-sac

 

viability. Following pollination several processes must

 

occur before fertilization is accomplished, including
pollen germination and tube growth. Flowers of 'Pandy' sour
cherry are open an average of 80 hours. Their pistils
become receptive 12 to 13 hours after anthesis and remain
so for 48 to 130 hours, while the anthers dehisce 13 to 44
hours after anthesis (62). Following deposition of the
pollen grain on the stigma, the grain swells and its coat
cracks allowing the pollen tube to grow into the style.
The time required for the tube to reach the micropyle
varies with species and with environmental conditions. It
varies from one (37) to 4 days (69) in sour cherry and
1 (78) to 5 days in sweet cherry (22), while for peach 4
days are required (38). Once the pollen tube reaches the
micrOpyle and enters the embryo-sac, it discharges its two
male gametes, one of which unites with the egg cell to
form the zygote, while the other fuses with the polar
nuclei to form the endosperm (29).

Bradbury (4) indicated that neither lack of polli-
nation nor failure of pollen tubes to reach the ovary were
important factors controlling fruit drop in sour cherry.

She found pollen tubes in the ovarian cavities of both

aborting and developing fruits 4 to 5 days after full
bloom. Thus slow pollen tube growth was not responsible
for lack of fertilization in first drop fruits. Ninety-
one percent of abscising fruits sampled 12 days after full
bloom contained two shriveled ovules, while all of the
developing ones contained at least one plump ovule. Only
6% of third drop fruits did not contain an embryo. She
concluded that abnormalities occur in the embryo-sac at
least as early as full bloom. The degeneration observed
in some flowers a day or two before blossoms Opened support
her conclusion. If her data are pooled, as much as 50%
of the total abscission can be attributed to early embryo-
sac degeneration.

Similar events occur in apricot (24), sweet cherry
(21), plum (17), apple (18) and peach (38). Eaton (21)
recorded the rate of embryo-sac degeneration in unpollinated
'Windsor' sweet cherry flowers following anthesis. At
anthesis almost all embryo-sacs had reached the 8-nucleate
stage; 2 days after anthesis over half of the flowers
collected had degenerate egg cells; 4 days after anthesis
80% of the embryo-sacs showed some irregularity and by
6 days after anthesis no functional egg cells could be
found. Eaton and Jamont (24) reported that only 22% of
apricot ovules sampled between anthesis and petal fall
contained functional egg cells. Eaton (21) stresses the
importance of pollination immediately after anthesis to

insure fertilization and fruit set.

10

In the sour cherry cultivar 'Korosi' the egg cells
are still viable 48 hours after anthesis, but they have
degenerated after 96 hours (65). Fruit set was highest
when flowers were hand pollinated within the first 24 hours
after anthesis; no fruit set occurred when pollination was
delayed more than 72 hours. In 'Lambert' sweet cherry,
mutant clones with a high pollen fertility had 62% normal
egg cells while those with low fertility had only 46% (23).

What triggers embryo-sac degeneration is unknown.
Harrold (38) observed shrinking of the nucellus at the
chalazal end of peach seeds while the embryo-sac was
apparently normal, indicating a possible disruption of the
vascular system supplying the ovule. This in turn might
cause egg cell degeneration. Similar observations have
been made in plum (17).

Reports as to the cause of abscission of apparently
normal fruits in the second and third drop are contradic-
tory. Dorsey (17) suggested that the second drop of plum
results from a lack of fertilization, while Bradbury (4)
found some fruits with embryos in cherry. Even less is
known as to the cause of the third drop. Abscising peach
fruits do not exhibit any apparent differences in structure
in comparison with developing fruits (38), embryo size
being the only observable difference. Simons and Chu (7)
suggested that the amount of placental tissue was important
in apple and that formation of an abscission layer

through the funiculus at the suspensor cell may be the

11

first phase of embryo abortion and fruit dr0p. Weinbaum
and Simons (84), comparing persistent versus potential drop
fruits of apple, showed that at the time a fruit stops
growing (an indication that it will abscise), no evidence
of degeneration or functional change was evident in the
embryo or the endosperm. Plum (1?) and peach (38) fruits
from the second and third drops contain seeds in which the
integuments have begun to turn brown at the chalazal end.
Browning extends towards the micropylar end as degeneration
proceeds. All of these observations suggest that in the

course of embryo abortion, the initial disorder occurs

elsewhere than in the embryo itself. Therefore, embryo
abortion probably is a result rather than the cause of
fruit abscission.

c) Diseases. Various fungi, bacteria, viruses and
other microorganisms can reduce production potential of
sour cherry (26, 35). While most can be controlled by
spray programs, some, including necrotic ring spot virus
and yellows virus,cannot. Their effect on growth and yield
has been reported (12, 49, 64). Tree to tree transmission
of viruses can occur through the pollen (6, 30, 49, 64).
Pollen from virus-infected trees is less effective in
setting fruit than that from healthy trees (80, 82). Total
sterility of sour cherry flowers may occur in trees
infected with necrotic ring spot virus (80).

d) Competition between flowers. Numerous reports

 

suggest that competition between flowers or fruits controls

12

set (4, 17, 70, 85). Therefore a freeze which reduces
flower density should reduce competition and increase set
of the remaining non-injured flowers. Sax (70) noted that
a larger percentage of apple flowers set fruit when
blossoms were thinned prior to hand pollination. Bradbury
(3, 4) reported that percentage fruit set of sour cherry
was greater in years when bloom density was reduced by
winter injury. However, using data published by Gardner
(28), I have calculated the correlation coefficient (r)
between percent survival following freezes versus percent
set of surviving flowers. The value r = 0.438 is non-
significant at p = 0.05 for these observations. Thus com-
petition cannot explain all observations and other factors
must also be involved.

Competition among flowers within buds has been
reported. Bradbury (4) noted that early thinning to one
blossom per bud increased percent set of sour cherry.
Howlett (43) increased fruit set of apple flowers from 3%
(untreated) to 50% by removing all flowers but one on each
cluster. The terminal flower set better than did laterals
and its presence reduced the set of the laterals.
Srivastava (74) found no differences between setting poten-
tial of terminal versus lateral pear flowers; however,
those in the central part of the inflorescence set best.
In grape the highest percent set occurred in flowers
opening the first day (66). When whole clusters were

considered, about 70% of the berries developed from

l3

flowers opening the first 2 days. Selective removal of
flowers opening the first, second or third day did not
increase set; therefore competition was not a factor.
Thinning of the fruits is a commercial practice to
increase size and/or color of fruits. Little is known as
to its effect on fruit retention because it is usually done
after "June" drop, that is, after most of the drop has
occurred. Howlett (44) thinned apple fruit clusters to 1
to 4 lateral fruits about a month before June drop. As the
number of fruits left per cluster increased the percentage
of fruits remaining after June drop decreased. He concluded
that reducing fruit competition early in the season largely
eliminated June drop. Zucconi (90) removed two-thirds of
the l-year-old branches and one-third of 2-and 3-year-old
branches on peach trees before anthesis, as well as two-
thirds of the fruits set 2 weeks after bloom. Only 23 to
31% of the fruits left on these trees abscised, while 77 to
99% of the fruits on control trees, in which no branches
or fruits were removed, abscised. Therefore, reducing
fruit load early in the season reduces subsequent fruit
drop in apple and peach.

e) Competition between fruit set versus current

 

season vegetative growth. Fruit set occurs at the same time
as shoot growth, and the two processes supposedly compete.
However, Goff (34) showed that growth of the terminal bud

on fruit spurs did not prevent setting of sour cherry

fruits, as spurs that made more than 2.5 cm growth during

14

the fruit setting period set fruit as well as did those with
less than 2.5 cm growth.

f) Fruit set and flower bud position. Buds on sour
cherry may occur on one-year-old shoots or on spurs on older
wood. Flower bud production on spurs accounts for about
60% of total yield (67, 68, 77); however, relative setting
ability of flowers on spurs versus those on one-year wood
has not been evaluated. Roberts (68) mentioned that flowers
on sour cherry shoots did not set as well as those on spurs,
but no data were presented. Diaz (unpublished data)
observed that 25-31% of flowers on shoots set fruit while

those on spurs of 2,3— and 4-year-old wood set 19-25%.

External Factors Affecting Set

 

a) Temperature. This is the main environmental

 

factor controlling fruit set in fruit trees, and it exerts
its effects in various ways. After rest is broken, micro-
sporogenesis of sour cherry begins when daily temperatures
exceed 5 to 6°C (56). Sour cherry pollen germinates well
at 20° but is retarded by temperatures below 10° (34).
Pollen germinates freely at 9° and the tube rapidly grows
through the style. In sunny warm weather (15 to 22° and

9 to 12 hours of sunshine) the longevity of the sour cherry
ovule is 2 to 3 days, while during cool overcast weather

(4 to 12°) longevity may be 4 to 6 days (60). Thompson and
Liu (75) observed that both initial fruit set and ovule

longevity in plum were inversely correlated with post bloom

15

temperature. Although ovule longevity is prolonged when
temperatures are low, pollen tube growth is retarded, off-
setting any beneficial effect on set. Similar observations
have been made in bean (63).

The main adverse effect of temperature on sour
cherry production is spring freeze injury to the flowers.
The temperature at which 50% of the flowers are killed
increases rapidly as the buds swell, reaching -5°C prior to
bud scale separation and -3° at full bloom (15). Not all
blossoms on a tree are at the same stage of development at
any given time, and the amount of injury depends to a
considerable extent on the percentage of opened versus
unopened flowers.

b) Light. Several reports show that shading sour
cherry treespso as to reduce light intensity up to 50% for
2 to 3 weeks beginning at bloom, has no effect on pollen
germination or tube growth (37, 69). However, the effect
on fruit set has been contradictory, Gray (37) observing
no effect while Lengord (50) and Roberts (68) noted a
reduction in set.

c) Cultural practices. Nutrition plays a key role

 

in tree yield and is closely related to tree vigor.
Nitrogen application increases yield of sour cherry (5, ll,
77) but this may reflect an effect on vegetative growth,
increasing the number of nodes where flowers can occur,
rather than an actual increase in fruit set. In

'Schattenmorelle' sour cherry nitrogen applications

16

increased both the total number of flowers per tree and the
number of flowers per inflorescence (53). Wierszyllowski
(86) reported that sour cherry trees treated in the fall
with N-P-K and some minor elements dropped less fruit the
following year. Fall applications of boron are effective
on increasing set in Italian prune (7) and sweet cherry

in Oregon (Westwood, personal communication).

Pruning can affect tree size, spur and flower bud
formation, leaf area and fruit size,depending on severity
and timing (29). Sour cherry orchards in Michigan are
often left unpruned after initial training. Recently,
Kesner et a1. (47) reported that hedging of sour cherry
trees before bloom increased both percent fruit set and
yield in the year of treatment.

Although chemicals are effective in increasing set
of some fruits (73, 83), no significant or consistent
results have been obtained in stone fruits (13, 39). Some
positive effects have been reported with self-incompatible
sour cherry cultivars following application of auxin and/or

gibberellins (59, 79).

Summary

Sour cherry production is erratic due to various
factors of which the most important is freeze injury to the
flowers. Considering that a relatively small percentage

of the surviving flowers yield mature fruit, there is a

17

need to evaluate more critically what controls fruit set,
and to find methods to increase it.

Efficient pollination is essential for rapid fer-
tilization of the egg cell, as the longevity of the ovule
after anthesis is limited. This can be achieved by intro-
ducing bees and possibly by interplanting pollinizers. The
cause of rapid ovule degeneration is unknown. Although
nutritional status of the tree has been implicated as a
possible cause, little evidence is available to support
this hypothesis. Competition between flowers and/or fruits
may also reduce set, but available data are contradictory.

Some critical work needs to be done to establish
the relationship between nutrition and set, as well as the
importance of environmental factors. Such studies should
include evaluations of flower formation and ovule longevity
as well as all other processes involved in fruit develop-
ment.

In the work to be described, experiments were
designed to provide additional information on some of the
factors that are reported to affect fruit set including
competition, nutrition, growth regulators and flower bud
formation. The hypothesis that fruit set is predetermined

at or near bloom was also evaluated.

LITERATURE CITED

Anderson, J. L., G. L. Ashcroft, R. E. Griffin, E. A.
Richardson, 8. D. Seeley, D. R. Walker, R. W. Hill,
and J. F. Alfaro. 1976. Final report to four
corners regional commission on reducing fruit
losses by low spring temperature. Utah Agr. Expt.
Sta.

 

Blake, M. A. 1925. The growth of the fruit of the
Elberta peach from blossom bud to maturity. Proc.
Amer. Soc. Hort. Sci. 22:29-39.

 

Bradbury, D. 1925. Notes on the dropping of immature
sour cherry fruits. Proc. Amer. Soc. Hort. Sci.
22:105-110.

 

 

. 1929. A comparative study of the developing

and aborting fruits of Prunus cerasus. Amer. J;

Bot. 16:525-542.

Bryant, L. R., and R. Gardner. 1937. Fertilizer
trials with sour cherry under limited irrigation.
Proc. Amer. Soc. Hort. Sci. 35:347-351.

 

Cameron, H. R., J. A. Milbrath, and L. A. Tate. 1973.
Pollen transmission of Prunus ringspot virus in
prune and sour cherry orcharas. Plant Dis. Rept.
57:241-243.

 

Chaplin, M. H., R. L. Stebbins, and M. N. Westwood.
1977. Effects of fall-applied boron sprays on
fruit set and yield of 'Italian' prune. Hort-
Science 12:500-501.

Collins, M. D., P. B. Lombard, and J. W. Wolfe. 1978.
Effects of evaporative cooling for bloom delay on
'Bartlett' and 'Bosc' pear tree performance. g;
Amer. Soc. Hort. Sci. 103:185-187.

 

Corgan, J. N., and F. B. Widmoyer. 1971. The effects
of giberrellic acid on flower differentiation,
date of bloom and flower hardiness of peach. .1;
Amer. Soc. Hort. Sci. 96:54-57.

 

 

18

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

19

Coston, D. C. 1976. The use of gibberellic acid
sprays in altering flowering and fruiting of the
sour cherry (Prunus cerasus L. cv 'Montmorency').
Ph.D. Dissertation, Michigan State University.

 

Crocker, T. F. 1971. The effect of nitrogen, potas-
sium and SADH on yield, quality and vegetative
growth of sour cherry (Prunus cerasus L., var.
Montmorency). Ph.D. Dissertation, Michigan State
University.

 

Davidson, T. R., and J. A. George. 1965. Effects of
necrotic ring spot and sour cherry yellows on the
growth and yield of young sour cherry trees. Can.
J: Plant Sci. 45:525-535.

 

Dennis, F. 6., Jr. 1972. Physiological control of
fruit set and development with growth regulators.
Acta Hort. 34:251-259.

 

. 1976. Trials with ethephon and other

growth regulators for delaying bloom in tree

fruits. J: Amer. Soc. Hort. Sci. 101:241-245.

 

, W. S. Carpenter, and W. J. Maclean. 1975.
Cold hardiness of 'Montmorency' sour cherry
flower buds during spring development. Hort-
Science 10:529—31.

Detjen, L. R. 1926. Physiological dropping of
fruits. Delaware Agr. Exptx Sta. Bul. 143.

 

 

Dorsey, M. J. 1919. A study of sterility in the
plum. Genetics 4:417-488.

1929. The relation between embryo sac
development and the set of fruit in the apple.
Proc. Amer. Soc. Hort. Sci. 26:56-61.

 

Drescher, W., and G. Engel. 1976. Einfluss der
Bestaubung von Schattenmorellen durch die Honig-
biene auf den Ertrag. Erwerbsobstbau 18:19-20.
(Hort. Abst. 46:9051).

Drinkard, A. W., Jr. 1909. Fruit-bud formation and
development. Annu. Rept. Virginia Agr. Expt. Sta.
pp. 159-205.

 

 

Eaton, G. W. 1959. A study of the megagametophyte in
Prunus avium and its relation to fruit setting.
Can. J, Plant Sci. 39:466-476.

 

 

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

~33.

34.

20

. 1962. Further studies on sweet cherry
EmBryo sacs in relation to fruit setting. Re t.
Ontario Hort. Expt. Sta._and Prod. Lab. pp. -38.

 

 

. 1968. Embryo sac development in relation
to pollen fertility in radiation induced Lambert
cherry mutants. Rad. Bot. 8:515-517.

 

, and A. M. Jamont. 1965. Embryo sac
development in the apricot, Prunus armeniaca L.
cv. Constant. Proc. Amer. Soc. Hort. Sci. 86:
95-101.

 

Fletcher, S. W. 1900. Pollination in orchards.
Cornell Univ. Agr. Expt. Sta. Bul. 181.

 

Freeman, J. A., H. A. Daubeny, and R. Stace. 1969.
Increased pollen abortion caused by viruses in
four red raspberry cultivars. Can. J; Plant Sci.
49:373-374.

Gardner, V. R. 1913. A preliminary report on the
pollination of sweet cherry. Oregon Agr. Expt.
Sta. Bul. 116.

 

 

. 1936. Factors influencing the yields of

Montmorency cherry orchards in Michigan. Michigan

Agr. Expt. Sta. Special Bul. 275.

 

 

, F. C. Bradford, and H. D. Hooker. 1939.
Fundamentals of fruit production. McGraw Hill
Book Co., Inc. 788 pp.

Gilmer, R. M. 1965. Additional evidence of tree-to-
tree transmission of sour cherry yellow virus by
pollen. Phytopathology 55:482-483.

 

, and R. D. Way. 1960. Pollen transmission
of necrotic ring spot and prune dwarf virus in
sour cherry. Phytopathology 50:624-625.

Goff, E. S. 1899. The origin and early development
of the flower in the cherry, plum, apple and pear.
16th Agnu. Rept. Wisconsin Agr. Expt. Sta.
pp. 289-303.

 

. 1900. Investigation of flower buds. 17th
Annu. Rept. Wisconsin Agr. Expt. Sta. pp. 266-285.

 

. 1901. A study of certain conditions
affecting the setting of fruits. 18th Annu. Rept.
Wisconsin Agr. Expt. Sta., pp. 289-303.

 

 

35.

36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

21

Gourley, J. H., and F. S. Howlett. 1941. Modern
fruit production. The Macmillan Co. 579 pp.

Gracza, P., and M. Gergely. 1973. Some questions of
flower organization in sour cherry. Acta Agron.
22:366-375.

 

Gray, G. F. 1933. Relation of light intensity to
fruit setting in the sour cherry. Michigan Agr.
Expt. Sta. Tech. Bul. 136.

 

 

Harrold, T. J. 1935. Comparative study of the
developing and aborting fruits of Prunus persica.
Bot. Gaz. 96:505-520.

Hartmann, H. T. 1950. Tests with growth-regulating
chemicals for increasing fruit set and yield in
olives. Proc. Amer. Soc. Hort. Sci. 55:181-189.

 

Hedrick, U. P. 1915. The cherries of New York. 22nd

Annu. Rept. State 9f New York, Dept. Agr. Vol. 2,
Part II.

 

Hitchcock, A. E., and P. W. Zimmerman. 1943. Summer
sprays with potassium a-naphthaleneacetate retard
opening of buds on fruit trees. Proc. Amer. Soc.
Hort. Sci. 42:141-145.

 

Hootman, H. D. 1930. Recent discoveries in pollina-
tion methods and practices and their influence
upon greater yields of desirable fruits. Proc.
Maryland State Hort. Soc. 33:24-36.

 

Howlett, F. S. 1928. Fruit setting in the Delicious
apple. Proc. Amer. Soc. Hort. Sci. 25:143-148.

 

 

. 1931. Effect of thinning before the June
rop upon fruit production. Proc. Amer. Soc.
Hort. Sci. 28:605-609.

 

Hull, J., Jr., and L. N. Lewis. 1959. Response of
one-year-old cherry and mature bearing cherry,
peach and apple trees to gibberellin. Proc. Amer.
Soc. Hort. Sci. 74:93-100.

 

, D. Ricks, D. Smith, E. McManus, J. Lincoln,
F. Klackle, W. Maclean, H. Better, and G. Antle.
1973. Fruit, vegetables, bees and pollination
now and in 1985. Michi an Agr. Ex t. Sta. and
C002. Ext. Serv. Researc Rgpt. .

 

47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

57.

58.

22

Kesner, C. D., C. H. Hansen, and S. B. Fouch. 1978.
Mechanical summer tipping as a method of con-
trolling sour cherry tree size: a preliminary
report. Fruit Var. J; 32:26-28.

 

Kester, D. E., and W. H. Griggs. 1959. Fruit setting
in the almond: the pattern of flower and fruit
drop. Proc. Amer. Soc. Hort. Sci. 74:214-219.

Klos, E. J., and K. G. Parker. 1960. Yields of sour
cherry affected by ring spot and yellow viruses.
Phytgpathology 50:412-415.

 

Lengord, L. R. 1935. Seasonal influences upon the
effect of shading in regards to setting of sour
cherry fruits. Proc. Amer. Soc. Hort. Sci. 33:
234-236.

 

 

Lipe, W. N., O. Wilke, and 0. Newton. 1977. Freeze
protection of peaches by evaporative cooling in
the post rest, pre-bloom period. J: Amer. Soc.
Hort. Sci. 102:370-372.

 

 

Marshall, R. E., S. Johnston, H. D. Hootman, and H. M.
Wells. 1929. Pollination of orchard fruits in
Michigan. Michigan Agr. Expt. Sta. Bul. 188.

 

Matzner, F. 1971. Einfluss steingender Stickstoff-
gaben auf die Zahl der gebildeten Blutenstade und
Bluten beider 'Schattenmorelle' in Grossgefassen.
Erwerbsobstbau 13:73-77. (Hort. Abst. 42:461).

 

McGregor, S. E. 1976. Insect pollination of culti-
vated crOp plants. U.S.D.A. Agric. Handbook 496.
411 pp.

Michigan Crop Reporting Service. 1978. Michigan
agricultural statistics, 1978. 0.8. Dept. Agric.
and Michr Dept. Agric. CRSB-78-02}

 

 

 

Mikhailov, T., and S. Topchiiski. 1975. Studies on
the date of microsporogenesis in some fruit
species. Sweet and sour cherry. Gradinarska i
Lozarska Nauka 12(8):l9-27. (Hort. Abst. 47:1212).

 

 

Miller, M. B. 1977. Comparison of models for pre-
dicting end of rest of flower buds and use of
evaporative cooling to delay bloom in sweet
cherry (Prunus avium L.). M.S. Thesis, Michigan
State University.

Modlibowska, I. 1972. Effect of growth regulators on
plum and cherry trees. Acta Hort. 34:203-205.

 

59.

60.

61.

62.

63.

64.

65.

66.

67.

68.

69.

70.

71.

Expt. Sta. Bul. 415.

23

Nyeki, J. 1973. Fruit set promoted by chemical
induction in Pandy sour cherry. Acta Agron. 22:
207-209.

. 1974. Megyfajtak viragai termoinek es
porzoinak ivarerettsege I. Kerteszti Egyetem
Kozlemenyei 38(6):135-l45. (Hort. Abst. 45:8152).

 

 

, and M. Soltesz. 1977. Effect of the dis-
tance and proportion of the pollen donor variety
on fruit setting and fruit yield in Pandy sour
cherry. Acta Agron. 26:87-89.

 

Nyujto, F., and B. Banai. 1974. A Pandy meggy
viragzasmenetenek "mikrofenologiaja". G umolc-
stermesztes 1:175-189. (Hort. Abst. 46:89I).

 

Ormrod, D. P., C. J. Woolley, G. W. Eaton, and L. H.
Stobbe. 1967. Effect of temperature on embryo
sac development in Phaseolus vulgaris L. Can. J;
Bot. 45:948-950.

 

Parker, K. G., K. D. Brase, G. Schmid, T. H. Barksdale,
and W. R. Allen. 1959. Influence of ring spot
virus on growth and yield of sour cherry. Plant
Dis. Rept. 43:380-385.

 

Pejkic, B. 1972. Vitalnost zenskog gametofita u
visnje kereske (P. cerasus L.). Jugoslovensko
vocarstvo 5(17/18):39I-403. (Hort. Abst. 43:3448).

 

 

Pratt, C. 1973. Reproductive system of 'Concord' and
two sports (Vitis laprusca Bailey). J; Amer. Soc.
Hort. Sci. 98:489-496.

 

 

 

Roberts, R. H. 1922. Better cherry yields. Wisconsin
Agr. Expt. Sta. Bul. 344.

 

 

 

. 1930. Sour cherry fruiting. Wisconsin Agr.

 

 

Sandsten, E. P. 1909. Some conditions which influence
the germination and fertility of pollen. Wisconsin
Agr. Expt. Sta. Res. Bul. 4.

 

 

 

Sax, K. 1921. Studies in orchard management. II.
Factors influencing fruit development in the
apple. 37th Annu. Rept. Maine Agr. Expt. Sta.
B31. 298. pp. 53-84.

Shoemaker, J. S. 1928. Cherry pollination studies.
Ohio Agr. Expt. Sta. Bul. 422.

 

 

 

72.

73.

74.

75.

76.

77.

78.

79.

80.

81.

82.

83.

24

Simons, R. K., and M. C. Chu. 1968. Ovule develop-
ment in the apple as related to morphological and
anatomical variation in supporting tissues. Proc.
Amer. Soc. Hort. Sci. 92:37-49.

 

 

Soost, R. K. 1958. Gibberellic acid on mandarin.
Calif. Agric. 12(5):5.

Srivastava, D. N. 1938. Studies in the non-setting
of pears. I. Fruit drop and the effect of
ringing, dehorning and branch bending. J: Pom.
and Hort. Sci. 16:39-62.

Thompson, M. M., and L. J. Liu. 1973. Temperature,
fruit set and embryo sac development in 'Italian'
prune. J: Amer. Soc. Hort. Sci. 98:193-197.

Tufts, W. P., and E. B. Morrow. 1925. Fruit-bud
differentiation in deciduous trees. Hilgardia 1:
1-14.

Tukey, H. B. 1927. Response of the sour cherry to
fertilizers and to pruning in the Hudson River
Valley. New York State Agr. Expt. Sta. Bul. 541.

 

. 1933. Embryo abortion in early-ripening
varieties of Prunus avium. Bot. Gaz. 94:433-468.

Ugolik, M. 1975. Regulatory wzrostu w procesach
zawiazywania i rozwijv owocow wisni. Roczniki
Akademii Rolniczej ! Poznaniu No. 56. 50 pp.
(Hort. Abst. 47:5290).

 

Vertesy, J., K. Gyorgy: and J. Nyeki. 1974. A
gyurusfoltossag virusok hatasa a Montmorency es
Pandy meggyfajtak generativ ciklusara. Gyumoles-
termesztes 1:191-201. (Hort. Abst. 45:9224).

 

Way, R. D. 1968. Pollen incompatibility groups of
sweet cherry clones. Proc. Amer. Soc. Hort. Sci.
92:119-123.

, and R. M. Gilmer. 1963. Reductions in
fruit set on cherry trees pollinated with pollen
from trees with sour cherry yellows. Phyto-
pathology 53:399-401.

 

Weaver, R. J., and W. D. Williams. 1950. Response of
flowers of Black Corinth and Thompson Seedless
grapes to applications of plant growth regulators.
Bot. Gaz. 111:477-485.

 

84.

85.

86.

87.

88.

89.

90.

25

Weinbaum, S. A., and R. K. Simons. 1974. An ultra-
structuralevaluation of the relationship of
embryo/endosperm abortion to apple fruit abscis-
sion during the post-bloom period. J: Amer. Soc.
Hort. Sci. 99:311-314.

 

 

, and R. K. Simons. 1976. Relationship of
seed number to fruit set in apple--an alternative
hypothesis. Fruit Var. J;_30(3):82-84.

 

Wierszyllowski, J. 1977. Wplyw preparatu Wuxal na
wzrost i owocowamie wisni Nefris. Referatrvhyi
Zhurnal 7.55.1030. (Hort. Abst. 48:1140).

Wocior, S. 1976. Badania biologii pylku wytwarzanego
przez kwiatz wisni zakwitajace w roznych fazach
kwitnienia. Acta Agrob. 29(1):69-84. (Hort.
Abst. 47:1213).

. 1976. Badania nad wybranymi zagadnieniami
biologii kwitnienia i owocowania wisni. Cz. III.
Niektore czynniki wplywajace na zapylenie wisni.
Roczniki Nauk Rolnicgych, A 101(4):63-77. (Hort.
Abst. 47:5289).

 

 

, T. Mitrut, Z. Opiat, and J. Woloszyn. 1976.
Badania kwitnienia i owocowania wisni. Roczniki
Nauk Rolniczych, A 101(4):63-77. (Hort. Abst.
47:5289).

 

 

Zucconi, F. 1975. Reassessment of the relationship
between hormonal and developmental changes during
abscission with particular reference to peach
(Prunus ersica L. Batsch) fruit. Ph.D. Disserta-
tion, Micfiigan State University.

SECTION I

EFFECT OF FLOWER.AND FRUIT DENSITY ON FRUIT
SET AND ABSCISSION OF SOUR CHERRY (PRUNUS

CERASUS L. CV. MONTMORENCY)

EFFECT OF FLOWER AND FRUIT DENSITY ON FRUIT
SET AND ABSCISSION OF SOUR CHERRY (PRUNUS
CERASUS L. CV. MONTMORENCY)
Abstract

No correlation was established between percentage

of sour cherry (Prunus cerasus L. 'Montmorency') pistils

 

killed by freezes and percent fruit set of the surviving
flowers. Random removal of two-thirds of the flower buds
to simulate frost injury had no significant effect on final
percentage fruit set in 3 consecutive years. Approximately
25% of the flowers which survived freezes yielded mature
fruits regardless of flower density. The abscission pat-
terns of flowers and immature fruits were not altered by
flower bud thinning. Neither fruit thinning nor defolia-
tion 2 weeks after bloom affected abscission of fruits.
Competition between flowers and/or fruits is therefore not
a factor in fruit set of 'Montmorency' sour cherry. Within
clusters, flowers which opened early set better than those
which opened late. Selective removal of flowers within
clusters according to their opening sequence did not
increase the fruit setting potential of those which
remained, indicating that competition within clusters also

is not a factor in sour cherry fruit set.

26

27

Nonuniform annual cropping is common in the
Michigan sour cherry industry, mainly because of Spring
freezes. In addition, shedding of flowers or immature
fruits could be so heavy some years that yield would be low
even in the absence of damaging freezes.

Uniform cropping might be achieved by either
a) delaying bloom to avoid freeze or b) controlling the
fruit setting process. Bloom delay has been achieved both
by using growth regulators (4, 9) and by evaporative
cooling with overtree sprinklers (3, 13, 14). Although
both methods have reduced the probability of freeze injury,
side effects often reduce the potential of flowers to set
fruit. The causes of fruit set are still obscure, but
competition between flowers and/or fruits has been sug-
gested as one controlling factor (2, 6, 7, 10, 11, 19).
Bradbury (2) reported a higher fruit set in sour cherry in
years when winter injury reduced bloom density. She also
found that removal of flowers within clusters at bloom
increased set. However, Gardner's (7) data show no correla-
tion between extent of freeze injury and percent fruit set
of surviving flowers. The effect of competition between
flowers within clusters has been evaluated in apple.
Leaving one apple flower per cluster at bloom results in
much higher percent set than does leaving two, three or
more flowers (10). Also the terminal apple flower, which
Opens first, sets better than lateral flowers, and its

presence reduces the setting potential of laterals. The

28

flowers in the middle part of the pear cluster set better
than those either more apical or more basal (18). The
highest percent set in grape flowers occurs in those
opening on the first day, later flowers setting half as
well (15).

Thinning apple (11) and peach (20) flowers and/or
fruits early in the season reduces abscission of the
remaining fruits, suggesting that competition is a factor
in fruit set.

This work was designed to determine the effect of
flower and fruit density on fruit set and to establish the

relative setting ability of flowers within clusters.

Materials and Methods

 

The 'Montmorency' trees used for treatments were in
a commercial orchard at Mears, Oceana County, Michigan, and
were 16 years old in 1976. Terminal vegetative growth
was 20-35 cm in length.

Effect of Fregge Injury on Set
of Surviving Flowers

 

To establish the relationship between extent of
freeze injury and set of surviving flowers, one limb with
a base diameter between 0.75-1.25 cm and length of about
40-60 cm was selected on each of ten uniform trees in the
spring of 1977 and eight in 1978. Two hundred flower buds
per limb were counted beginning at the apex of the limb.

In both years freezes (-3° to -6°C) occurred before bloom.

29

Two days after full bloom, the number of both injured and
surviving flowers were recorded. At harvest, persisting
fruits on each limb were counted and percent set determined.
Effect of Flower or Fruit

Density and Defoliation
on Fruit Set

 

 

 

In order to determine if flower or fruit density or
defoliation had any effect on set either in the same or in
subsequent seasons, three plots, each with 4 trees of
uniform growth, vigor and yield were established in the
summer of 1975 and one limb was selected on the north,
south, east and west sides of each tree. Treatments
applied to branches the following year were as follows:

a) control--no treatment; b) two-thirds of the flower buds
removed at bud swell; c) two-thirds of the leaves removed
2 weeks after full bloom; d) two-thirds of the fruits
removed 2 weeks after full bloom. Each treatment was
applied to one limb on each tree, using a Latin Square
design, and 200 flower buds were counted on each limb.

The number of flowers injured by freezes were recorded at
bloom, and all results were expressed on the basis of
living flowers. Limbs were shaken gently every 2 to 3
days following full bloom to dislodge abscising flowers
and fruits, and persisting fruits were counted. Treat-
ments were continued on the same limb on 1 plot in 1977, and
on another plot in 1978 (Table 1); each year the number

of buds, flowers and fruits were counted. In order to

30

Table 1. Experimental Arrangement of Treatments to Evalu-
ate the Effect of Flower and Fruit Density and
Defoliation Within Limbs on Fruit Set.

 

 

Plot Year(s) of Year Data Total No.
Treatments Collected Trees
I 1976 only 1975 4
II 1976 and 1977 1977 4
III 1976, 1977
and 1978 1978 4

 

verify the dr0p pattern of flowers and fruits, sheets were
placed one one side of the tree (North, South, East or West)
on the ground under four 7-year-old trees on an adjacent
plot and abscised fruits were collected at 2 to 4 day inter-
vals from bloom until harvest without shaking the limbs.

Effect of Flower Density and
Position Within Clusters on

Fruit Set

 

 

 

Sour cherry flowers open in sequence within
clusters (Figure 1). Comparisons were therefore made of
the fruit-setting ability of flowers in relation to time of
opening. Flowers were classified as: A, first to open;

B, second to open; and C, third to cpen within a cluster.
In 1977 and 1978, flower clusters on 4 trees were selected
and their flowers color coded with adhesive tape so as to
classify their fruiting performance according to the
sequence of flower opening. Also, during the spring of

1977 uniform l7-year-old trees were selected and assigned

31

Figure 1. Differential opening of flowers within a cluster.

32

 

33

to a randomized block design with 4 replications (trees)
and 7 treatments, using only clusters with 3 flowers. To
evaluate the effect of flower density and position on fruit
set, the following treatments were applied to individual
limbs: no flowers removed, C removed, B removed, A removed,
A and B removed, B and C removed, A and C removed. The
same design was used in 1978 with seven 7-year-old trees
(replicates). Fruit set was evaluated several times during
the early summer and again at harvest.
Embr o-Sac Development
Within Clusters

In 1978 embryo-sac development was evaluated to
determine if late developing flowers were more likely to
contain non-functional sacs. At anthesis of the most
advanced flower within each cluster, each flower was color
labeled according to its opening sequence and samples were
taken at intervals thereafter. Flowers were fixed in FAA
as described by Johansen (12) and stored at 7°C. Pistils
were then dehydrated using tertiary butyl alcohol (12),
embedded in paraffin, and cut serially at 12 microns
thickness. The ribbon was affixed to the slide with
Weaver's solution (16). Sections were stained in Safranin-
Fast green (12) and later examined with a light microscope.
Embryo-sacs were classified according to whether the egg
cell was a) differentiated, or b) irregular or degenerate.
Nine to 12 flowers of each type (A, B, and C) were examined

on each sampling date.

34

Tetrad Formation in Anthers of
FIOwers Within Clusters

 

 

To evaluate the time of microsporogenesis in rela-
tion to flower position within the bud, flower buds were
collected at bud swell in 1978 and processed as described
above. Anthers were examined with a light microscope and
flowers were classified as to whether tetrads were present

or not.

Results and Discussion

 

Freeze Injupy

 

In both 1977 and 1978, percentage fruit set of
flowers which survived freezes decreased as the proportion
of flowers killed increased (Figure 2). However, correla-
tion coefficients were nonsignificant in both years. As
data were available for only 8 to 10 limbs, significant
values might have been obtained with more replications.
This relationship might be expected if sub-lethal frost
injury occurred, and internal tissues such as the ovules

were damaged without injury to the pistil itself.

Flower Cluster Density

Removal of two-thirds of the flower buds did not
affect final percent fruit set (Table 2). Although all
treatments reduced fruit set slightly, in no case were
differences significant at 5%. These data do not agree
with those of Bradbury (2) who found that low flower

density increased set of sour cherry. Removal of

35

Figure 2. Freeze injury to flowers vs fruit set at harvest
in 'Montmorency' sour cherry, 1977 and 1978.

SET OF NON-INJURED FLOWERS

CENT

40

10

36

 

 

1011: o, —
nous-0.5::
[I no.“

‘.’.: .. .-.

A neon-0.4.x
n «m

 

l l 1 l l

 

10 20 30 40 .0

$ FREEZE INJURY

 

37

.moEwH v HON Hmuoam

.Ho>ma wm um DCMOAMHcmHm mumz mDCOEumouu coo3uon moOCOHOMMAU 0c .mumow aflauwzu

 

 

o.¢m omha H.mm mmma N.>N mmma GODMAHOMOQ
o.m~ mamm o.m~ mama o.hm oamm coccflnu muwsnm
m.m~ omoa w.m~ mum w.mm mmoa ooncwnu moan Hmzoam
o.am ONHN N.m~ mmma o.om «mom mcoz
muo3oam mum3oam >muo3oam
Dom w mcw>wq .02 now w mcw>wn .02 now w mcH>HA .oz

 

GT 0
mhma .bhma .whmH shad .mhmd chad u Eum MB

 

ucofiummua mo mummy

 

.ucoaumona mom moons e no comm co mosm Ho3on com mcwumom

pawn moo N.>H=ncH ouooum How omuoouuoo moon .muuono Hoom .aocouosucoz. mo

pom uflsum ommucoouom ucoooomnsm co Eoon “ovum mxomz N mo>moq Ho muflsum osu mo
mouwnalo39 no .Eoon oHOMmm moom uozoam onu mo mouflnalo3e mo Hm>osom mo poommm .N canoe

38

buds in 1976 only did not alter percentage fruit set sig-
nificantly, even though the number of flowers per limb was
reduced by half. Competition between clusters is therefore
not a factor in controlling fruit set, and any injury to
flowers will reduce potential yield. When flower buds were
thinned 2 or 3 years in succession, fruit set was again
similar to that of the control. Therefore, fruit load
does not appear to affect fruit set the following year.
Fruit thinning or partial defoliation 2 weeks after full
bloom did not affect fruit set (Table 2), so competition
between fruits does not appear to be a critical factor
for a fruit to persist. Considering the pattern of fruit
drop (see below), induction of abscission probably had
already occurred 2 weeks after full bloom.

The abscission pattern of flowers and immature
fruits for 1976 was similar to that reported by Gray (8)
(Figure 3A). The first wave of abscission of flowers began
12 days after full bloom and comprised 20% of the total
flowers and fruits abscised. The second wave began at 20
days, lasted for 12 days, and accounted for about 75% of
the total drops. No definite third wave was observed, but
a few fruits continued to fall from 32 days after full
bloom until harvest. The pattern was similar in 1977, but
the peaks were earlier (Figure 3B). Temperature following
bloom may affect the pattern, as temperatures were higher
in 1977 than in 1976. Flower thinning did not affect the

pattern of abscission (Figures BA, BB). Abscission of

39

Figure 3. Effect of flower bud thinning on flower and fruit
drop pattern, 1976 (A) and 1977 (B). Data based
on number of persisting fruits.

FLO'EOI AID FNITI “OCR!“ (‘0' TOTAL DROPS,

40

 

 

— COITIOI.

---- FWEI was
new“.

 

 

10 '
I
I
l
A l I I |
10 20 30 ‘0 .0
one arm- mu noon
‘0 '
— counsel.
-__- now" was
rmuuo
30 ‘
2U "
10 "

 

 

 

 

DAVE AFTER FULL ILOOI

41

sour cherry flowers and fruits has been attributed to early
embryo-sac degeneration (2) and/or to embryo abortion (2).
Whatever the cause, competition between flowers or fruits
does not appear to be involved.

The drop pattern obtained by collecting flowers or
fruits from sheets beneath the trees did not differ
appreciably from that based on persisting flowers and

fruits on tagged limbs (Figure 4).

Flower Density Within Clusters

 

Clusters with all three flowers present (no treat-
ment) in 1977 and 1978, were classified as to fruiting
performance according to the sequence of flower Opening
(Table 3). More than one-third of the clusters set no
fruit, while only 4% set all flowers. When only one flower
set per cluster, flowers A or B were twice as likely to be
retained as was C. If 2 flowers set fruit, A plus B were
retained more often than were A plus C or B plus C.
Combining data for all flowers, flowers A and B set equally
well, but C was less likely to set fruit.

Hand removal of flowers yielded similar data
(Table 4) indicating again that flower C had a lower poten-
tial to set whether other flowers are left on the cluster
or not. Thus fruit-setting potential is not affected by

competition with other flowers in the cluster. Differences

in set between treatments were not significant in 1978.

Figure l.

53

Scanning electron micrographs of critical point
dried apices of sour cherry (Prunus cerasus L.
cv 'Montmorency') showing deveIopmental changes
during flower initiation. A. Initial phase of
change from vegetative to reproductive stage by
rounding of the apex, with bract primordium
(BP), June 10. x600. B. Flattening of the
apex, June 15. x440. C. Floral primordia
(FP) developing in the axil of each bract
primordium, June 28. x510. D. Floral prim-
ordia evident in 3 bracts and a 4th beginning
to form, June 30. x410. E. Ovate stage of
flower primordia, July 3. x320. F. Round
stage of flower primordia, July 10. x300.

 

43

 

 

 

 

40

FULI. ILOOI

DAVE AFTER

 

P D b

 

.00 '-

m m m
‘

08.0.8.4 ’53: 081 3:9: a4h°h

 

Table 3. Classification of Flower Clusters by Fruiting
Performance According to Sequence of Flower

Opening.

44

 

Cluster with

Percent of Clustersz

 

 

1977 1978
No mature fruit 38.5 37.4
AY only 13.8 13.0
B only 12.3 10.2
C only 6.2 6.8
A and B 15.4 12.2
A and C 4.2 7.5
B and C 4.2 8.8
A, B, and C 4.2 4.1
Means for:
All A's 37.0 36.7
All B's 35.6 35.4
All C's 18.0 27.2

 

2Data collected from 65 (1977) and 147 (1978) labeled

flower clusters.

yA, B, and C: lst, 2nd, and 3rd flower to open within a

cluster.

45

.Ho>ma wm .ummu 3 m.>ox:9 an whom» canvas :Owuoumoom cmmzx

.uoumoao m casuw3 ammo ou um3on cum com com .uma ”U can m .<>

.mumzoam ooa moo woumm>umn mufloum mo HonEs: mm pom uwsumn

 

 

 

 

 

o.n~ m.mm m.om H.ma o.m~ ~.m~ cum:
m~.s~ ~.h~ .. u- hm.va m.va u- u- saco u
mm.mm I- m.mm n- nm~.h~ I- ~.s~ u- saco m
mm.qm nu I- m.vm nm~.m~ -u 1. «.mm saco «
mn.m~ m.m~ m.~m u- an».ma v.4a v.m~ u- u can m
m~.~m m.s~ u- s.om mm.mm m.am u- s.mm u can a
om.mm .. H.mm m.vv m~.mm nu 4.4m o.mm m can a
ms.Hm G.Hm m.mm s.om xnmv.am m.ma m.q~ m.m~ u can .m .4

new: 6 m a new: 0 m a
wmcflcwmfimm

mhmH hhmH mHO3OHh
numm w

4'1"! 1‘! ||,l|

.muo3on mcflcflmem mo Dom com: mumumoau cflnuwz Hm>OEmm HOSOHE mo nommmm

Ea."

.v THEME

46

 

Embryo-Sac Develo ment of
Flowers Within a CIuster

A higher percentage of normal embryo sacs was found

 

in flowers A and B (more advanced) than in flower C on all
sampling dates (Table 5). Regardless of time of flower
opening, the percentage of flowers with differentiated

egg cells declined with time. These data support the
hypothesis that flowers A and B set better than C because
of their greater embryo-sac normality.

Tetrad Formationgin Anthers of
Flowers Within a Cluster

 

 

The largest flowers (most advanced) within a bud
formed tetrads 1-2 days earlier than the smallest ones,
indicating than even though flowers may appear similar
within the bud, they may differ internally in stage of

development.

The time of flower initiation may affect fruit-
setting potential. The sour cherry inflorescence is a
raceme bearing one to five flowers (2) and scanning elec—
tron microscope observations (5) indicate that differences
in development are apparent up to the time of sepal
differentiation, although no external differences are
evident thereafter. The flower which opens last and sets

least is probably the last to differentiate within a bud.

47

Table 5. Effect of Flower Position on Egg Cell Normality,

1978.z

 

Days in Relation to Anthesis

 

 

Flower y Flower
Pos1tion _3 _2 0 3 5 7 Mean
(Percentage with differentiated
egg cells)
A 90 35 89 70 55 45 70.8ax
B 90 . 85 80 60 55 45 69.2a
C 85 75 70 55 45 40 61.7b
Date mean 88a 82b 77c 62d 52e 43f

 

2Nine to twelve embryo-sacs examined per date per flower

type.

yA, B, and C: lst, 2nd and 3rd flower to open within

cluster.

XMean separation in rows and columns by Tukey's w test,

5% and 1%, respectively.

10.

LITERATURE CITED

Bradbury, D. 1925. Notes on the dropping of immature
sour cherry fruits. Proc. Amer. Soc. Hort. Sci.
22:105-110.

 

. 1929. A comparative study of the developing

and aborting fruits of Prunus cerasus. Amer. J;

 

Bot. 16:525-543.

Collins, M. D., P. B. Lombard, and J. W. Wolfe. 1978.
Effects of evaporative cooling for bloom delay on
'Bartlett' and 'Bosc' pear tree performance. J;
Amer. Soc. Hort. Sci. 103:185-187.

 

Dennis, F. G., Jr. 1976. Trials with ethephon and
other growth regulators for delaying bloom in tree
fruits. J, Amer. Soc. Hort. Sci. 101:241-245.

 

Diaz, D. H., H. P. Rasmussen, and F. G. Dennis. 1978.
Scanning electron microscope observations on
flower bud differentiation in sour cherry (Prunus
cerasus L.). HortScience 13:382.

 

Dorsey, M. J. 1919. A study of sterility in the
plum. Genetics 4:417-488.

Gardner, V. R. 1936. Factors influencing the yields
of Montmorency cherry orchards in Michigan.
Michigan Agr. Exp. Sta. Special Bul. 275.

 

Gray, G. F. 1933. Relation of light intensity to
fruit setting in the sour cherry. Michigan Agr.
Expt. Sta. Tech. Bul. 136.

 

Hitchcock, A. E., and P. W. Zimmerman. 1943. Summer
sprays with potassium o-naphthaleneacetate retard
opening of buds in fruit trees. Proc. Amer. Soc.
Hort. Sci. 42:141-145.

 

 

Howlett, F. S. 1928. Fruit setting in the Delicious
apple. Proc. Amer. Soc. Hort. Sci. 25:143-148.

 

 

48

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

49

. 1931. Effect of thinning before the June
drop upon fruit production. Proc. Amer. Soc.
Hort. Sci. 28:605-609.

 

 

Johansen, D. A. 1940. Plant microtechnique. McGraw
Hill Book Co., Inc.

Lipe, W. N., O. Wilke, and 0. Newton. 1977. Freeze
protection of peaches by evaporative cooling in
the post-rest, pre-bloom period. J: Amer. Soc.
Hort. Sci. 102:370-372.

 

 

Miller, M. B. 1977. Comparison of models for pre-
dicting end of rest of flower buds and use of
evaporative cooling to delay bloom in sweet cherry
(Prunus avium L.). M.S. Thesis, Michigan State
University.

 

Pratt, C. 1973. Reproductive system of 'Concord' and
two sports (Vitis labrusca Bailey). JL_Amer.
Soc. Hort. Sci. 98:489-496.

 

 

Sass, J. E. 1958. Botanical microtechnique. Iowa
State College Press, Ames, Iowa.

Sax, K. 1921. Studies of orchard management. II.
Factors influencing fruit development in the
apple. Maine Agr. Expt. Sta. Bul. 298. pp. 53-84.

 

Srivastava, D. N. 1938. Studies in the non-setting
of pears. I. Fruit drop and the effects of
ringing, dehorning and branch bending. J: Pom.
and Hort. Sci. 16:39-62.

Weinbaum, S. A., and R. K. Simons. 1976. Relation-
ship of seed number to fruit set in apple--an
alternate hypothesis. Fruit Var._J; 30(3):82-84.

 

Zucconi, F. 1975. Reassessment of the relationship
between hormonal and developmental changes during
abscission with particular reference to the peach
(Prunus persica (L.) Batsch) fruit. Ph.D. disser-
tation, Michigan State University.

 

SECTION II

SCANNING ELECTRON MICROSCOPE OBSERVATIONS OF
FLOWER BUD DIFFERENTIATION IN SOUR CHERRY

(PRUNUS CERASUS L. CV. MONTMORENCY)

SCANNING ELECTRON MICROSCOPE OBSERVATIONS OF
FLOWER BUD DIFFERENTIATION IN SOUR CHERRY
(PRUNUS CERASUS L. CV. MONTMORENCY)

Abstract

Axillary buds on 'Montmorency' sour cherry (Prunus
cerasus L.) spurs and shoots on current season's growth
were sampled and prepared for scanning electron microscopy.
Five weeks after full bloom the first evidence of change
from the vegetative to the reproductive stage appeared as a
rounding of the apex. Flower primordia arose in the axils
of bracts in an acropetal pattern. Bracts and flower
primordia continued to form until all available space on
the apex had been occupied. The flower primordia changed
from ovate to round as development proceeded. Sepal
primordia became evident forty-five days after the first
signs of initiation, and later petal primordia arose,
alternating with sepal primordia. Stamen primordia
developed in concentric rings below the petal primordia.
Pistil initiation did not occur until the middle of

September.

The morphological changes occurring during flower
bud formation in fruit trees have been described by various
workers beginning in the late 18008 (4, 6, 7, 9) using
medial longitudinal or transverse stained sections and

light microscopy.
50

51

In sour cherry the first visible signs of flower
initiation occur about 5-6 weeks after full bloom (9)
and differentiation of most flower parts is complete about
8-10 weeks later. Timing varies depending on location and
tree vigor. Inflorescences generally contain 2 to 4
flowers arranged in a corymb (6).

Studies by DeHertogh et a1. (1), Emino and Rasmus-
sen (5) and Scholefield and Ward (8) of flower development
in Easter lily, carnation and grape, respectively, have
illustrated the value of the scanning electron microscope
(SEM) in studying flower develOpment. Advantages include
increased depth of field and.magnification and resolution of
the entire apex.

This study describes the morphological changes
which occur in the developing shoot apex of sour cherry

during flower formation.

Material and Methods

 

Buds from lB-year-old 'Montmorency' sour cherry
trees were collected periodically during 1976 in a commer-
cial orchard at.Mears,Michigan. Full bloom occurred on
May 10 in 1976. Ten trees were selected for uniform size
and vigor, and a total of 50 buds were collected at each
sampling date. Their scales were removed and the apex was
placed in a glass vial containing distilled water. Within
24 hrs of sampling, the apices were dehydrated using a

10-step graded ethanol series (10 to 100%). The apices

52

were left at least 20 minutes in each solution. Following
three changes of 100% ethanol, samples were critical point

dried (CPD Denton DCP-l) using clean liquid CO The buds

2.
were then stored in a vacuum desiccator over anhydrous
CaSOA. Before the samples were examined in the SEM, buds
were further dissected under a stereo light microscope to
expose the apex, mounted on aluminum SEM stubs using 'Tube
Coat' (G. C. Electronics Co., Rockford, Ill.) and then
sputter coated with 40-60 nm of gold. A Super II SEM
(International Scientific Instrument Co.) operated at an
accelerating voltage of 15 kV was used to view the samples.
Initial observations indicated that lateral buds
on current season's wood and buds on spurs of 2-, 3- or
4-year-old wood were similar in stage of flower development.
Lateral buds were easier to manipulate and were therefore

the primary material used. At least 10 specimens were

examined for each sampling date.

Results and Discussion

On June 10, 1976, the first sampling date, shoots
were about 10 cm in length. Although some vegetative
apices were evident, most of them were desiccated and cells
appeared concave. For most deciduous fruit trees, including
sour cherry, cross sections of the apex exhibit a smooth
rounded crown of meristematic tissue more or less enclosed
by primordial leaves, bracts or bud scales (4, 6, 9). Such

a structure is evident in Figure 1A. As the season

42

Figure 4. Daily absolute fruit drop for 'Montmorency' sour
cherry, 1977. Data based on number of falling
fruits.

54

 

55

progressed, the apex became broadly rounded or flattened
(Figure 1B) with two well-developed bract primordia and
others being formed in an apparently spiral fashion. The
youngest bract primordium occurred at the apex of the
meristem, indicating an acropetal pattern of formation.
The flattening of the apex was the first noticeable evi-
dence of the change from vegetative to reproductive phase
as previously reported (4, 6, 9) and occurred at a similar
time, that is, 5 weeks after full bloom. The individual
flower primordia later formed in the axils of these bracts
(Figure 1C). The individual flower primordia continued to
develop through August and September (Figures 1D, 1E).
Differences in stage of development were evident among
flowers. The only evidence for some of the flower prim-
ordia was the presence of the bract. About 18 days after
the first signs of initiation were apparent, flower
primordia were ovate in shape (Figure 1E) then became round
(Figure 1F, 2A). Forty-five days after the first signs of
initiation,sepa1 primordia appeared (Figure 2B) as a penta-
gonal whorl. The rounded apex gradually became concave as
previously described (7). Immediately within the sepal
primordia five small petal primordia arose (Figures 2C,
2D). The central part of the meristem was no longer con-
cave but flat, and the stamen primordia developed in
circular layers immediately within the petal primordia
(Figure 2D). At this time differences in stage of organo-

genesis between flowers within apices were still apparent

Figure 2.

56

Scanning electron micrographs of critical point
dried apices of sour cherry (Prunus cerasus L.
cv. 'Montmorency') showing developmental changes
during flower differentiation. A. All apex
space occupied by three floral primordia,

July 20. x410. B. Calyx evident as sepal
primordia (SP) in a pentagonal whorl, July 30.
x300. C. Corolla and stamens evident as petal
primordia develop within sepal primordia,

August 15. x165. D. Stamen primordia developing
below petal primordia (PP), August 15. x400.

E. Pistil initial (PI) arising from flat apex,
September 10. x360. F. All floral organs
present, September 29. x150.

 

57

 

58

some having large stamens while others had yet to differen-
tiate petal primordia. Near the middle of September, the
pistil primordium was initiated on the flat surface of the
apex (Figure 2E), and continued expanding with the other
floral parts (Figure 2F).

Most of the reproductive apices produced 3 to 4
flowers. This characteristic seems to be determined by the
apex size, which will allow the development of only a cer-
tain number of bract primordia. In some instances, even
though a bract primordium developed, the flower in its axil
either did not develop at all (Figure 2A) or developed
slowly.

Within an apex flowers developed differentially up
to a certain stage (anther and probably pistil initiation),
after which no external differences were evident. However,
internal differences do seem to occur as Diaz (2) has
observed that at bud swell tetrad formation in the anthers
occurs consistently 2 days earlier on the most expanded
flower while embryo-sac degeneration is significantly more
frequent in the least advanced flower. The external
differences apparent in flower development within a bud
probably are responsible for the differences in fruit

setting potential observed by Diaz (3).

LITERATURE CITED

De Hertogh, A. A., H. P. Rasmussen, and N. Blakely.
1976. Morphological changes and factors influen-

cing shoot apex development of Lilium lon iflorum
Thunb. J; Amer. Soc. Hort. Sci. 101:463-g7I.

 

Diaz, D. H. 1978. Effect of flower and fruit density
on fruit set and abscission of sour cherry
(Prunus cerasus L. cv. Montmorency). In press.

, and F. G. Dennis, Jr. 1978. Effect of
flower density on fruit set and abscission in
'Montmorency' sour cherry (Prunus cerasus L.).
HortScience 13:383.

 

 

Drinkard, A. W. 1909. Fruit-bud formation and
development. Annu. Rept. Virginia Agr. Expt. Sta.
pp. 159-205.

Emino, E. R., and H. P. Rasmussen. 1971. Scanning
electron microscope studies of the shoot apex in

Dianthus car 0 h llus L. cv. Scania. J; Amer.
Soc. Hort. Sc1. 56:253-256.

Goff, E. S. 1899. The origin and early development
of the flowers in the cherry, plum, apple and
pear. 16th Annu. Rept. Wisconsin Agr. Expt. Sta.
pp. 289-303.

 

Gracza, P., and M. Gergely. 1973. Some questions of
flower organization in sour cherry. Acta Agron.
22:366-375.

 

Scholefield, P. B., and R. C. Ward. 1975. Scanning
electron microscopy of the developmental stages
of the Sultana inflorescence. Vitis 14:14-19.

Tufts, W. P., and E. B. Morrow. 1925. Fruit-bud

differentiation in deciduous trees. Hilgardia
1:1-14.

59

APPENDICES

APPENDIX A

PREDICTING PERSISTENCE OF SOUR CHERRY

FRUITS BY OVARY DIAMETER

PREDICTING PERSISTENCE OF SOUR CHERRY

FRUITS BY OVARY DIAMETER

Stone fruits such as sour cherry exhibit a double
sigmoid growth curve which can be divided into 3 stages
(1, 5, 6). During each stage different events are occur-
ring within the developing embryo. Investigators have
attempted to distinguish between fruits which will persist
versus those that will abscise using such criteria as size,
color or removal force (2). However, by the time such
differences are evident the process of abscission may be
well advanced.

Flowers and immature fruits of sour cherry drop in
two or three waves, different populations occurring in
each wave (1, 3, 4). Knowing when induction of abscission
occurs would be useful in attempting to either enhance or
reduce abscission.

In order to compare the growth rates of persisting
and abscising fruits and to determine the time of induc-
tion of abscission, 150 flowers were labeled at full
bloom in 1977 and ovary diameter was measured 13 days
later and at 2 to 10 day intervals thereafter until

either abscission or harvest. The trees used were

60

61

17 years old and were part of a commercial orchard at Mears,
Michigan. Data were plotted as means for groups of fruits
that dropped on a certain date.

The growth curve of persisting fruits was double
sigmoid (Figure A-l). Fruits with a diameter of 1.5-3.3 mm
13 days after full bloom (AFB) abscised 15-17 days AFB,
while those 3.5-6.5 mm in diameter abscised 18-23 days AFB.
These fruits were representative of the first and second
wave drops, respectively. The growth rates of fruits that
abscised late in the growing period (30 days AFB) were
indistinguishable from those of persisting ones up to 18
days AFB. Growth then ceased. None of the fruits which
were 7 mm or less in diameter 13 days AFB reached maturity,
whereas almost all of those larger than 7 mm persisted
until harvest (Table A-l). Fruits which fell in the first
2 drops never approached the size of those that persisted.
Their diameters were only half of those of persisting
fruits 13 days AFB, suggesting that either the flowers were
defective or that induction occurred at bloom or shortly
thereafter. For late abscising fruits, induction of
abscission must have occurred at least 12 days before
separation, based upon growth rates.

In studies to reduce abscission of sour cherry
flowers and fruits, observations or treatments should be
started at bloom or shortly thereafter, for induction of

abscission apparently occurs very early.

62

Figure A-l. Growth curves for groups of persisting and
abscising fruits, 1977.

63

On On

2:85 08.0.0m0<
Catt h8Uhu.¢¢mt

IOOJI 443$

Ov On

CUht<

O>(O

 

Op

 

(WW) UBLBNVIO AUVAO

64

Table A-1. Abscission Date and Percent Set at Harvest of
'Montmorency' Sour Cherry Fruits in Relation to
Ovary Diameter 13 days AFB, 1977.

 

 

Ovary Date of Mature
Diameter (mm) No. Fruits Abscission Fruits
13 Days AFB (Days AFB) Harvested (%)
0-2.0 0 -- --

2.1-3.0 8 18 0.0
3.1-4.0 7 18 0.0
4.1-5.0 3 18 0.0
5.1-6.0 2 25 0.0
6.1-7.0 l 25 0.0
7.1-8.0 8 -- 100.0
8.1-9.0 13 30 85.0
9.1-10.0 31 -- 100.0
10.1-11.0 10 -- 100.0

11.1-12.0 1 -- 100.0

 

LITERATURE CITED

Bradbury, D. 1929. A comparative study of the
developing and aborting fruits of Prunus cerasus.
Amer. J; Bot. 16:525-542.

 

Bukovac, M. J. 1971. The nature and chemical promo-
tion of abscission in maturing cherry fruit.
HortScience 6:385-388.

 

Diaz, D. H., and F. G. Dennis, Jr. 1978. Effects of
flower density on fruit set and abscission in
'Montmorency' sour cherry (Prunus cerasus L.).
HortScience 13:383.

 

 

Gray, G. F. 1933. Relation of light intensity to
fruit setting in the sour cherry. Michigan Agr.
Expt. Sta. Tech. Bul. 136.

 

 

Harrold, T. J. 1935. Comparative study of the
developing and aborting fruits of Prunus persica.
Bot. Gaz. 96:505-520.

 

 

Tukey, H. B. 1935. Development of cherry and peach
fruits as affected by destruction of the embryo.
Proc. Amer. Soc. Hort. Sci. 33:265-266.

 

 

65

APPENDIX B

EFFECTS OF NUMBERS OF TREE AND LIMB REPLICATES
AND OF NUMBER OF BUDS PER LIMB ON VARIABILITY

OF DATA FOR FRUIT SET OF SOUR CHERRY

EFFECTS OF NUMBERS OF TREE AND LIMB REPLICATES
AND OF NUMBER OF BUDS PER LIMB ON VARIABILITY

OF DATA FOR FRUIT SET OF SOUR CHERRY

Fruit set has been evaluated and expressed in
various ways. The Michigan Crop Reporting Service (3), in
making their survey for forecasting yields of sour cherry,
records fruit set from 600 sample trees, randomly selected
from all growing areas, using one limb per tree. In experi-
ments with cherries, data have usually been recorded as
numbers of fruits per 100 flower buds (l, 2). Treatments
are often applied to one limb on each of 4 trees and data
recorded for 100 to 200 flower buds per limb, counted from
the apex toward the base (1, 2, 4).

Experiments were designed to evaluate the minimum
number of trees, limbs per tree and buds per limb which
would yield a sufficiently small variance of the sample

mean to allow detection of differences among treatments.

Experiment 1

 

Four l8-year-old uniform trees of 'Montmorency'
sour cherry located at Mears, Michigan, were used in a
completely randomized design and ten limbs were selected

on each tree. Two hundred flower buds were counted from

66

67

the apex toward the base, the numbers of viable flowers
were recorded at bloom, and all persistent fruits were
counted at harvest. Values for fruits per 100 flowers were
subjected to a model II analysis of variance (5) to provide
an unbiased estimate of the variance among trees (S2t) and
within trees (821). These values were used to calculate

the variance of the sample mean (32;) according to the

formula:

where L = number of limbs, and T = number of trees.

Experiment 2

 

Five trees and four limbs per tree were selected
in a randomized block design using 18-year-old trees at
Mears,Michigan. On each limb, flower buds were counted
from the tip toward the base and labels were used to mark
25, 50, 150 and 200 buds. The numbers of flowers with no
visible injury were recorded at bloom, and the number of
fruits were counted at harvest. The data were converted
to percentage. Once the analysis of variance was calcu-

lated, the coefficients of variation (CV) were obtained.

68

Results and Discussion

 

Experiment 1

 

Values of $2; declined as the number of limbs per
tree increased from 1 to 10 (Table B-l), and the same was
observed as the number of trees increased. Using rela-
tively few limbs per treatment per tree and more trees is
more efficient than using more limbs per tree but fewer
trees. For example, the 52; values using 1 limb on each of
4 trees is similar to that obtained using 3 limbs on each
of 2 trees, but only two-thirds as many total limbs need to

be used in the former case.

Experiment 2

 

Using a limb unit with only 25 flower buds yields
a high coefficient of variation (CV) of fruit set data
(Table B-2). The CV decreases as the number of buds per
limb increases from 25 to 100, then increases to plateau at
150 to 200 buds. There is about 1.3 times as much vari-
ability with 25 buds as with 50 buds. The low value at
100 buds is probably not valid, as values for 150 and 200
are no less than that for 50 buds. Therefore 50 buds per
limb appears to be the minimum number required for a

reliable estimate of fruit set.

69

 

 

 

 

m.H m.H o.m H.~ ~.~ v.~ h.~ H.m o.v h.o OH
H.N m.m m.m m.~ m.m h.m o.m m.m m.v w.h m
m.m q.~ m.~ o.m m.~ o.m m.m m.m o.m m.m m
n.~ m.~ m.m o.m ~.m v.m m.m m.v h.m m.m h
H.m N.m m.m m.m w.m o.v m.v m.m n.m H.HH w
m.m m.m o.v N.v m.v m.v m.m m.w o.m m.mH m
n.v m.v o.m m.m m.m o.w n.o m.h o.oH h.mH w
m.m v.o h.@ 0.5 v.h o.m m.m v.0H m.MH N.mm m
v.m h.m o.oH m.0H ~.HH o.NH v.MH m.mH o.o~ H.mm m
m.mH v.mH H.om o.H~ m.- H.v~ h.m~ m.Hm m.mm m.mm H
OH m w b w m w m N H momma
moms Mom mnEHH mo monasz «0 .oz
.QAAH .coaumoflammm Hod moons oH 6» H sues .m¢.ma u wm 6cm GH.mm u mm
SOHSB :H coHuoHsmom m cH pom uHoum ommucoouom mom AMNmV com: mHmEmm on» no
oocmHuo> oomeHumm map so come moo mnEHH poo momma mo HOQEEZ mo poommm one .Him OHQMB

70

Table B-2. Effect of the Number of Flower Buds per Limb
on the Coefficient of Variation (%) of Fruit
Set Data, 1978.

 

 

No. Flower Buds C2%Y.
25 34.0

50 26.0

10° 20.0

150 25.0

20° 26.0

 

LITERATURE CITED

Dennis, F. G., Jr. 1976. Trials of ethephon and other
growth regulators for delaying bloom in tree
fruits. J; Amer. Soc. Hort. Sci. 101:241-245.

 

 

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

 

Michigan Crop Reporting Service. 1975. Objective
yield survey. Tart cherry. U.S. Dept. Agric. and
Michigan Dept. Agric.

 

 

Miller, M. B. 1977. Comparison of models for pre-
dicting end of rest of flower buds and use of
evaporative cooling to delay bloom in sweet
cherries (Prunus avium L.). M.S. Thesis, Michigan
State UniverSiEy.

 

Snedecor, G. W., and W. G. Cochran. 1973. Statistical
methods. Iowa State University Press. 539 pp.

71

APPENDIX C

EFFECT OF NITROGEN FERTILIZATION ON VEGETATIVE
AND REPRODUCTIVE CHARACTERS OF SOUR CHERRY

(PRUNUS CERASUS L.)

EFFECT OF NITROGEN FERTILIZATION ON VEGETATIVE
AND REPRODUCTIVE CHARACTERS OF SOUR CHERRY

(PRUNUS CERASUS L.)

Nutrition, particularly the supply of nitrogen,
plays an important role in yield of cherries (l, 2, 4) but
few experiments have been designed to evaluate its effects
on fruit set p§£.§§.

To obtain such data for sour cherry, observations
were made in 1977 on 9-year-old 'Montmorency' trees
which had received various nitrogen levels for 4 consecu-
tive years (1974-1977): 0.56 Kg N per tree applied to the
soil in the fall (Ground), and 0.56 (100%) or 0.14 (25%)
Kg N per tree applied through trickle irrigation during
the summer. Experimental plots were located in a commercial
orchard near Traverse City, Michigan.

The nitrogen contents of leaves sampled in July
1977 were 2.8, 2.2 and 2.6% of the dry weight for ground,
100% and 25% treatments, respectively (3), while yields
in 1976 were 12.7, 10.9 and 9.1 kg/100 cm2 trunk area for
the same treatments.

Four trees per treatment were selected at random

for uniform size and vigor and data were recorded for 50 cm

72

73

of shoot length on each individual limb per tree. Only
terminal and lateral shoots more than 5 cm long were
measured. Parameters evaluated are indicated in Table C-l.
At bloom in 1977 the numbers of uninjured flowers were
counted, and fruit set was recorded shortly before harvest.
The only significant difference between treatments
was reduced vegetative growth in the 25% treatment in
comparison with the other two (Table C-l). Although differ-
ences occur in other observations, none were statistically
significant. In general, nitrogen fertilization appears to
stimulate growth and therefore increases the bearing area
of the tree. It also increases the number of flowers per
bud, especially in spur buds, and fruit number and set.

All these effects would tend to increase yield.

74

Table C-l. Vegetative, Flowering, and Fruiting Responses
of 9-Year-Old 'Montmorency' Sour Cherry Trees

to 3 Levels of Nitrogen,

1977.

 

Method of Application

 

 

 

 

 

 

 

 

 

Observation Ground Trickle Irrigation
0.56 Kg N 0.56 Kg N 0.14 Kg N

1976 Vegetative

growth Ten) 81.3az 76.8a 56.3b
No. flower buds/50 cmy

On shoots 47.0 44.3 35.8

On spurs 16.0 11.8 23.0

Total 63.0 56.1 58.8
No. flowerszflower bud

On shoots 2.3 2.5 2.3

On spurs 2.7 2.6 2.0
Total flowers/50 cm 150.0 142.2 131.2
Total fruits/50 cm 22.7 24.5 14.5
Percent set 28.3 32.0 23.8

 

 

zMean separation within

rows by Tukey's w test, P = 0.05.

y50 cm of shoot length, spurs disregarded.

LITERATURE CITED

1. Bryant, L. R., and R. Gardner. 1937. Fertilizer
trials with sour cherries under limited irrigation.

Proc. Amer. Soc. Hort. Sci. 35:347-351.

2. Crocker, T. F. 1971. The effect of nitrogen, potas-
sium and SADH on yield, quality and vegetative
growth of sour cherry (Prunus cerasus L., var.
Montmorency). Ph.D. Dissertation, Michigan State

University.
3. Kenworthy, A. L., and M. Smith. 1977. Fertilizing

orchards through trickle irrigation systems.
107th Annu. Rept. Michigan State Hort. Soc.,

pp. 73-76.

4. Tukey, H. B. 1927. Response of the sour cherry to
fertilizers and to pruning in the Hudson River
Valley. New York State Agr. Expt. Sta. Bul. 514.

75

APPENDIX D

GROWTH REGULATORS AND FRUIT SET OF SOUR

CHERRY (PRUNUS CERASUS L.)

 

GROWTH REGULATORS AND FRUIT SET OF SOUR

CHERRY (PRUNUS CERASUS L.)

Growth regulators have been used successfully to
increase the setting potential of some species of fruits
including grape (8), citrus (6) and pear (9). However,
inconsistent or poor results have been obtained with stone
fruits (2, 3). The growth regulators used have included

GAB' GA 2,4,5-TP, SADH, CCC and NAA. Timing is impor-

4/7'
tant and Degman and Batjer (l) and Westwood et a1. (9)
obtained responses in pear when auxin was applied as early
as the previous fall.

In cherries, growth regulators have had variable
effects on set. In sweet cherry (Prunus azipm L.) Misra
and Sharma (4) obtained a response with NAA applied at full
bloom. When GA3 and NAA were applied together at full
_bloom, fruit abscission was delayed but final set was
unaffected. In 'Pandy' sour cherry, a self-sterile culti-

var, GA and 2,4,5-TP applied together at bloom and 2 weeks

3
later promoted set (5). The use of 2,4,5-TP and Gibrescol

(GA + 6A3) increased set on the cultivars 'Podbielski'

l
and 'Hiszpanka' in Poland (7). Numerous attempts to

increase set of 'Montmorency', the leading commercial

76

77

cultivar in the United States, with growth regulators have
failed (Bukovac, Dennis, personal communication).

To evaluate the fruit setting response of 'Mont-
morency' sour cherry to growth regulators, 18-year-old
trees were arranged in 4 separate randomized blocks, each
with 4 replications (trees), in 1977. Sprays were applied
on May 5 (full bloom) in block I and on May 15 (petal fall)
in block II to determine their effects on fruit set in
1977, and on August 15 and October 9 in blocks III and IV,
respectively, to evaluate effects on fruit set in 1978.
Chemicals and concentrations are indicated in Table D-l.

Each treatment was applied with a hand sprayer
until run-off to one branch of each tree within a plot.

For plots I and II two hundred flower buds were counted

per treated branch from the tip towards the base and the
number of flowers which survived freezes was recorded. The
number of persisting fruits were recorded several times in
early summer and at harvest. In 1978 the same procedure
was used for plots III and IV but the numbers of persisting
fruits were recorded only at harvest.

Both full bloom and petal fall applications of GA3
and 2,4,5-TP increased set recorded 20 or 25 days after
full bloom, but did not affect final set significantly.
All other treatments were without effect on either 1977 or
1978 set. The effects of GA3 and 2,4,5-TP in delaying

abscission suggest that mixtures and/or multiple

78

applications of these chemicals might be more effective

than single treatments.

79

 

 

 

 

 

II II ON oHO ON oOO OOH
OO OH II II II II Ob
II II OH oOO 5N DON OO
ON HN ON oOO ON DON ON
Hm mm mm use mm 0mm m mcHamOmeucmm
HO ON ON oOO 5N anO OH
ON HO ON onNO 5N 8OO O OHIO.O.N
II II OO oOO OH 0NO OOH
ON ON II II II II Oh
II II ON ooOO NN oON OO
ON ON ON ONO ON 0ON ON h\O
ON OH 5N oOO 5N OOO O «0
II II ON oanO ON onOO OOH
HN OH II II II II Oh
II II II II ON oOO OO
OO OH ON oOO hN oQHO ON O
NN HN II II ON 0ON O 40
NN ON ON oOO hN xOON II mcoz
N N N H %N %H

m Honouoo OH umsmod OH am: an: Hemmv
>H HHH HH H .ocoo NHmostno

 

GOHHMOHHQQN mo mama 6cm unmEHHooxm

 

.H>H ocm HHH mucmEHnmmxmv OhOH no HHH pom H mucoaHHomxmv hhmH cH hunoco Room
.Nocmuosucoz. mo uwm uHsum :0 ssmH cH OmHHomd muoumHsmom nuzouw mo muommmm .Hun mHnma

80

C3039. COMUOHHCOUGOU

.OunuxHE on» on HOOOH

.HmHocHHHH .OOMOHEO .mOHHoumHoan Hyena: H.\O¢O maHm OGHCOOOHONcom—z

.O0.0 u m .umou 3 m.mmxza an m3ou cHnuH3 :oHumHmoOm cmmzx

.umm>umn um uOm uHsum n N «EOOHQ HHSO Houmm mama ON no ON HOV umm HOHHHGH n H4H

.wH.O um ucmuommuam ON COO3B OOCHOOGOO mGOHuaHOm HHNN

 

 

 

 

 

 

 

 

II II ON OQOO ON OON OOH
ON ON II II II II Oh
II II ON OnOO OH OHO OO
ON OH HN OHO OH OOO ON
ON ON ON ONO HN OON O 3GHHmEoum
N N N H N H
m umnouoo OH umsms< OH an: m an: Heady
>H HHH HH H .950 HOOHEOEU
coHHMOHHom« mo mama Ocm HGOEHHOmxm
.OoncHucou .HIQ OHnma

LITERATURE CITED

Degman, E. S., and L. P. Batjer. 1955. Delayed
effects of 2,4,5-trichlorophenoxypropionic acid

sprays on Anjou pears. Proc. Amer. Soc. Hort. Sci.
66:84-86.

Dennis, F. G., Jr. 1972. Physiological control of
fruit set and development with growth regulators.
Acta Hort. 34:251-259.

 

Hartmann, H. T. 1950. Tests with growth-regulating
chemicals for increasing fruit set and yield of
olives. Proc. Amer. Soc. Hort. Sci. 55:181-189.

 

Misra, L. P., and V. K. Sharma. 1972. Effect of
growth regulating substances on the control of
flowering and fruit setting in sweet cherry cv
Black Heart. Indian J: Hort. 29:292-297.

Nyeki, K. 1973. Fruit set promoted by chemical induc-
tion in Pandy sour cherry. Acta Agron. 22:207-209.

Soost, R. K. 1958. Gibberellic acid on mandarin.
Calif. Agric. 12:5.

 

Ugolik, M. 1975. Regulatory wzrostu w procesach
zawiazywania i rozwojov owocow wisni. Roczniki
Akademii w Poznaniu No. 56, 50 pp. (Hort. AEst.

"7“” :529'0) ."

Weaver, R. J., and W. D. Williams. 1950. Response of
flowers of Black Corinth and fruits of Thompson
Seedless grapes to applications of plant growth
regulators. Bot. Gaz. 111:477-485.

Westwood, M. N., P. B. Lombard, and L. D. Brannock.
1968. Effect of seeded fruits and foliar-applied
auxin on seedless fruit set of pear the following
year. HortScience 3:168-169.

 

81

"IllllllllllllllllllS