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University.

 

This is to certify that the

thesis entitled

YIELD INCREASES FOR ONCE-OVER HARVEST WITH

MULTIPLE-PISTILLATE FLOWERING IN PICKLING CUCUMBERS

presented by

Noe Alberto Uzcategui
has been accepted towards fulfillment
of the requirements for

M' 3' degree in .HDRIJLCIILILIRE

 

 

Date April 2]., 1978

 

0-7639

YIELD INCREASES FOR ONCE-OVER HARVEST WITH
MULTIPLE-PISTILLATE FLOWERING IN PICKLING CUCUMBERS

By

Noe Alberto Uzcategui

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

1978

ABSTRACT

YIELD INCREASES FOR ONCE-OVER HARVEST WITH
MULTIPLE-PISTILLATE FLOHERING IN PICKLING CUCUMBERS

By
Noe Alberto Uzcategui

Gynoecious cucumber (Cucumis sativus L.) F3 lines selected for

 

multiple-pistillate flowers per node were tested for yield potential.

Two preliminary experiments, one under greenhouse and the other under
field conditions, were carried out to determine yields of the F3 lines

in comparison to 3 commercial hybrids with single-pistillate flowers

per node. The increased numbers of pistillate flowers on the F3 lines
resulted in greater numbers of fruits per plant and reduced the per-
centage of fruit inhibition; and subsequently, more yield of pickling
cucumbers for once-over harvest than the commercial F1 hybrids. Develop-
ment of pickling cucumber hybrids with multiple-pistillate flowers per
node offers a new breeding possibility to increase yields for once-over

harvest systems.

Guidance Committee:
This thesis is condensed into a format suited and intended for
publication in the Journal of the American Society for Horticultural

Science.

ii

To my wife Eglee, and

to my son Noe Alfonso

iii

ACKNOWLEDGMENTS

The author extends his sincere appreciation to his major professor,
Dr. L. R. Baker, for his guidance and encouragement throughout the course
of his research and study, and also to committee members Drs. B. 8. Dean
and E. H. Everson for their valuable suggestions.

Sincere appreciation is extended to Dr. R. R. Neitzel for his valu-
able assistance of the computer analysis. Special thanks goes to Mrs.
L. Yarger, M. Dessert, and I. El-Shawaf for their invaluable help plant-
ing and maintaining research plots, and thanks also goes to all those
student workers who aided in data collecting.

He is indebted to the Foundation "Gran Mariscal de Ayacucho" of
the Republic of Venezuela for its financial support throughout the

pursuit of this degree.

iv

TABLE OF CONTENTS

Page
List of Tables ........................ vi
List of Figures ....................... viii
INTRODUCTION ......................... 1
MATERIALS AND METHODS .................... 3
RESULTS AND DISCUSSION .................... 8
CONCLUSION .......................... 35
LITERATURE CITED ....................... 36

LIST OF TABLES

Table Page

1 Pedigrees selected for F evaluation, which by obser-
vation, segregated F gynoecious recombinants with
multiple-pistillate flowers per node .......... 4

2 Outstanding individual F cucumber plants selected for
highest number of pistiliate flowers per node and self-
pollinated to produce F3 lines ............. 5

3 Number of pistillate flowers per node for selected indi-
vidual outstanding F plants in preliminary greenhouse
screening used to degive F3 lines ............ 9

4 Number of pistillate flowers from lO nodes per plant in
a greenhouse experiment with F lines of pickling cucum-
bers with multiple-pistillate flowers per node compared
to standard hybrid varieties .............. lO

5 Yield as number and weight (g) of fruits per plant from
a greenhouse experiment with F lines of pickling cucum-
bers with multiple-pistillate flowers compared to hybrid
varieties with single-pistillate flowers. Varieties
are ranked in Table by mean total fruits per plant . . . ll

6 Number of pistillate flowers pollinated per plant during
a period of 5 days in a greenhouse experiment with F
lines of pickling cucumbers with multiple-pistillate
flowers in contrast to hybrid varieties with single-

pistillate flowers ................... l3
7 Simple correlation coefficients for yield character-

istics of pickling cucumbers evaluated in a greenhouse

and field experiment .................. l5
8 Number of pistillate flowers per plant for To nodes and

number and weight of fruits per plant from 4 MSU lines
omitted from the field experiment due to a stand loss in
field plots ....................... 23

9 Number of pistillate flowers from 10 nodes per plant
from a field experiment with F pickling cucumber lines
selected for multiple-pistilla e flowers in contrast to 3
commercial hybrids with single-pistillate flowers. . . . 24

vi

Table
10

ll

l2

Page

Yield as number and weight (g) of fruits per plant

from a field experiment with F lines of pickling

cucumber with multiple-pistillgte flowers compared

to hybrid varieties with single-pistillate flowers . . 25

Mean comparison test of lines with multiple-pistillate
flowers per node (MP) and lines with a single-pistil-
late flower per node (SP) of pickling cucumbers. . . . 27

Comparison of pickling cucumber with multiple-

pistillate and single-pistillate flowers per node for
percentage of fruit inhibition for each pollination

day; greenhouse experiment .............. 29

vii

LIST OF FIGURES

Figure Page
l Effect of multiple and single-pistillate flowers per
node on the yield of pickling cucumber ......... l7
2 Effect of number of fruits set per plant on the weight
of these fruits in pickling cucumber .......... 19
3 Partial regression of yield, as weight of fruits per

plant (Y), on number of fruit per plant (X ) versus
total regression where X2 is number pistiliate flowers
per plant from lO nodes ................ . 2l

4 Percentages of fruit inhibition (——-) and fruit set
(---) in the cucumber plant during a 5-day pollination
period (MP is multiple-pistillate flowers and SP is single-
pistillate flowers per node). The correlations of
r = 0.98 are significantly different at the l% level
and r = 0.94 are significantly different at the 5% level 32

viii

INTRODUCTION

One of the major objectives of pickling cucumber research is to
enhance the female flowering habit of commercial cultivars so as to
further concentrate fruit set and increase yield for once-over mechanical
harvest (l,30). Yield of pickling cucumbers in this single harvest
system is influenced by the ability of plants to develop several fruit
simultaneously. This concentration of fruit set is unapparent in cur-
rent pickling cucumber hybrids since they usually produce one to two
marketable fruits per plant (l,5,7,26,28,30,37,28). Tiedjens (42) in
T928 was the first to report that the low number of fruits per plant
was due to an inhibitory effect by the first-set fruit. The presence
of a developing fruit exerted an inhibitory effect upon growth of sub-
sequent fruit as well as upon the production of pistillate flowers and
further vegetative growth of the plant. Since then, several researchers
have confirmed the same "inhibitory first-fruit effect" in Cucumis
sativus (3,4,5,6,7,l0,ll,l4,l5,l6,l7,l8,27,33,35,38,45) and other cucur-
bit species (9,l9,25,34). This fruit growth depression proceeds with
seed development in fertilized fruit, and remains until the seed coats
harden, whereupon the plant starts to exhibit signs of renewed vegeta-
tive growth, flowering, and fruiting (16.27.33).

Several ways to overcome fruit inhibition have been suggested.

The fruit may be picked or excised from the plant which removes the
inhibitory effect until the next fruit begins to develop when it will

again exhibit inhibition over other fruits (lO,l9,27,42). Gustafson

(17) demonstrated that parthenocarpic fruits had little inhibitory
effect on other fruit and confirmed McCollum's observations (27) that
developing fertilized ovules produced a growth inhibitor. Since auxins
have been suggested to be the growth inhibitor compounds several workers
have stimulated parthenocarpic fruit set with natural and synthetic
auxins and auxin transport inhibitors (3,4,5,6,12,18,33). Pike and
Peterson (35) and Denna (11) showed that genetically parthenocarpic
cucumber lines produced several fruits per plant which indicated that
parthenocarphy, at least partially, overcomes fruit-set inhibition.
Tiedjens (42) in 1928 and Cantliffe (4) in 1974 suggested that by
breeding varieties which develop many fruits simultaneously at the same
node, inhibition could be overcome. Whitaker and Davis (45) stated
that, within a particular cultivar, there is a correlation between the
number of flowers and the number of fruit produced. Yield, among other
factors, depends on (1) the ability of a variety to produce a large
number of flowers, (2) to produce them early, (3) to fertilize a high
percentage of the total number of pistillate flowers, and (4) to fertil-
ize those which appear early in the growing season. The objectives of
this research were: a) to breed gynoecious cucumber lines which pro-
duce multiple-pistillate flowers at the same node, b) simultaneously to
pollinate these large number of pistillate flowers over a short time
period so as to overcome "first-fruit inhibition," and c) consequently,
yield would be higher due to the increased number of fruit per plant

for pickling cucumbers used in once-over mechanical harvest systems.

MATERIALS AND METHODS

Plant material. In order to develop hermaphroditic pollen parents
necessary for the production of gynoecious hybrid seed, crosses of sev-
eral gynoecious lines with a Russian hermaphroditic line (MSU 4108H)
were made in 1971. It was observed that MSU 4108M produced multiple
hermaphroditic flowers per node and that a low frequency of gynoecious
F2 recombinants also produced multiple-pistillate flowers per node.
Based on this observation, the yield potential of several early genera-
tion gynoecious lines that express multiple-pistillate flowers per node
was measured (Table 1).

Evaluation and selection of F2 plants. On December 15, 1976

 

twelve F2 seeds of each selected F2 family were germinated in peat pots
with soil culture. Two weeks later, six seedling of the selected fami-
lies were transplanted into raised greenhouse soil benches. On February
1 the number of pistillate flowers per node per plant was counted from
the sixth to the tenth nodes. From this first evaluation, 44 gynoecious
plants with the highest number of pistillate flowers per node were sel-
ected out of the 542 plants initially planted. The number of pistillate
flowers on nodes eleven through fifteen were counted on February 21 for
the 44 selected plants. Sixteen outstanding plants from the second
evaluation were selected for self-pollination and seed increase (Table 2).
Lateral cuttings were taken from the selected individual plants for
rooting and cloning. The rooted and transplanted cuttings were treated
with GA4/7 (37) to induce staminate flowers for self-pollination and F

3
seed production.

Table 1. Pedigrees selected for F evaluation, which by observation,
segregated F gynoecious recombinants with multiple-pistillate
flowers per Node.

 

 

 

Greenhouse no. MSU pedigree - No. of families
4499 0y3 x 4108H 8
4500 713-50 x 4108H 12
4502 1830 x 4108H 14
4503 33930 x 4108H 18
4504 1530 x 4108H 11
4505 0y54 x 4108H 10
4508 8440 x 4108H 7
4795-1 0y54 x 4108H 2
4823-8 0y3 x 4108H 1
4824-1 0y3 x 4108H 1
4827-2 0y3 x 4108H 1
4836-2 350 x 4108H 1
4846-1 1830 x 4108H l

 

Total 87

Table 2. Outstanding individual F cucumber plants selected for highest
number of pistillate floaers per node and self-pollinated to
produce F3 lines.

 

 

 

Greenhouse no. Seed source MSU pedigree MSU line no.
7592-4 4503 33930 x 4108H 592-43
7598-1 4503 33930 x 4108H 598-10
7598-2 4503 33930 x 4108H 598-20
7598-3 4503 33930 x 4108H 598-30
7598-4 4503 33930 x 4108H 598-40
7602-3 4503 33930 x 4108H 602-30
7603-5 4503 33930 x 4108H 603-50
7604-4 4503 33930 x 4108H 604-40
7607-4 4503 33930 x 4108H 607-40
7608-2 4503 33930 x 4108H 608-20
7608-4 4503 33930 x 4108H 608-40
7612-3 4824-1 0y3 x 4108H 612-30
7644-2 4504 1530 x 4108H 644-20
7644-3 4504 1530 x 4108H 644-30
7648-3 4504 1539 x 4108H 648-30
7661-5 4502 1830 x 4108H 661-50

 

Greenhouse experiment. During the Summer of 1977, the yield

 

potential of the outstanding 16 individual F3 selections was tested
using a randomized complete block design with 3 blocks and 6 plants per
block for line tested. The lines were compared with four commercial
hybrid cultivars: Green Star (Harris Seed Co.), Premier and Pioneer
(Asgrow Seed Co.), and Kora (Nundems Zaden Co.). The first three
hybrids are currently used in Michigan for pickling cucumber production,
while the last one, Kora, is a pickling cucumber used in the Netherlands
which exhibits multiple-pistillate flowers per node (13,21). The seeds
were planted in peat pots with soil culture on June 29 and transplanted
into raised greenhouse beds on July 11. Plants were fertilized every
other week by irrigating with a solution containing 6 g fertilizer per
plant (20.0%N: 8.7%P: 16.6%K) to 4 1 water. The main stem of each

plant was trained vertically on a 2 m bamboo stake. All lateral branches
were pruned prior to pollination (34). Cucumber flowers were hand-
pollinated hithe morning with randomly mixed pollen from 2 staminate
flowers obtained from monoecious (MSU 8519) and androecious (MSU 5802A)
lines. All flowers on the main stem of each plant were pollinated when
the first flower opened at the sixth node and when subsequent flowers
opened over a 5-consecutive day period (8).

Harvesting was done on an ihdividual plant basis. Each plant was
harvested when at least one fruit reached 5 cm (2 inches) in diam
(28,30). The following data were collected: number and weight of
fruits per plant, number of pistillate flowers per node per plant from
the 6 through 15 nodes, and the number of pollinated flowers per day.
The number and weight of the fruits harvested according to each pollina-

tion day was then calculated.

Field experiment. The sixteen selected lines were evaluated in

 

the field using a randomized complete block design with 3 blocks and
single plots. Soil samples were taken from each block prior to plant-
ing for analysis by the MSU Soil Testing Laboratory (45). Results
indicated that standard fertility recommendations were warranted (30).
Forty seeds were planted per plot of 7.62 m (25 feet) long and l m
(3.33 feet) wide rows were used to eliminate plant population as a
yield factor. Twenty-five plants per plot were desired, but due to
severe bird attacks and soil crusting during germination, a minimum of
10 plants were obtained. The monoecious line, MSU 8519, was planted
as the outside guard row and as every third plot to provide an abundant
pollen source for bee pollination. Standard cultural practices (30)
were used throughout the growing season and irrigation was supplied
as needed. Harvesting was done when one or two fruits per plot reached
5 cm (2 inches) in diam (28,30). The following data were collected:
number and weight of fruits per plot, and the number of pistillate
flowers per node per plant (nodes 6 through 15) from a random sample of
four plants per plot.

Analyses of variance were performed using the computer program
SPSS (33) of the Michigan State University Computer Laboratory. Mean
comparisons were made by Duncan'siMultiple Range Test for equal sample
sizes, and by the t and F tests for unequal sample size (42). Correla-
tion and regression analyses were done following the procedures ex-

plained by Little and Hills (24).

RESULTS AND DISCUSSION

Evaluation and selection of F2 plants. The number of pistillate
flowers per node from the selected 16 individual outstanding F2 plants
ranged from 4.3 (MSU 607-40) to 2.5 (MSU 612-30) (Table 3). Other
characteristics such as fruit and spine color, spine type, and plant
growth were also noted, but are not reported here since they are not of
interest to the immediate objectives of this research.

Greenhouse experiment. The total number of pistillate flowers

 

produced per 10 nodes by each line varied from 2.1 to 41.3 and their
differences were highly significant (Table 4). The 15 MSU lines sel-
ected for multiple-pistillate flowers produced more pistillate flowers
than any of the four commercial hybrid cultivars. The line MSU 598-20
was discarded because the plant stand was lost. The MSU lines with
the highest total numbers of pistillate flowers were 604-40, 598-30,
602-30, 598-10, and 598-40 ranging from 41.3 to 37.6 total pistillate
flowers for the 10 nodes. In contrast, the four commercial hybrids
ranged from 9.6 to 2.1 pistillate flowers for the same 10 nodes.

Highly significant differenfes were also found for the number and
weight of fruit produced per plant (Table 5). The MSU lines with mul-
tiple-pistillate flowers per node produced higher yields than any of
the commercial hybrids. The total number of pistillate flowers pollinated
per plant during the 5-pollination days also was highly significant for
the lines and varieties (Table 6). The MSU lines with multiple-

pistillate flowers provided higher number of flowers for pollination;

Table 3. Number of pistillate flowers per node for selected individual
outstanding F plants in preliminary greenhouse screening used
to derive F3 ines.

4k

 

MSU line no. No. pistillate-flowers/nodez
407-40 4.3 f 1.49
604-40 3.4 f 1.26
661-50 3.4 f 2.06
608-20 3.3 f 0.67
598-40 3.2 f 0.63
608-40 3.2 f 0.91
644-30 3.2 f 1.39
603-50 3.0 f 0.47
602-30 3.0 f 0.81
598-20 3.0 f 1.33
644-20 2.9 f 0.73
598-10 2.8 f 0.91
648-30 2.8 f 1.03
592-40 2.8 f 1.03
598-30 2.5 f 1.08
612-30 2.5 f 1.35
Range 4.3 to 0.7

 

2Each value is the mean and the standard deviation of the number
of pistillate flowers per node from 10 nodes (nodes 6 through 15).

10

Table 4. Number of pistillate flowers from 10 nodes per plant in a
greenhouse experiment with F lines of pickling cucumbers
with multiple-pistillate flowers per node compared to standard
hybrid varieties.

Variety Pistillate flowers/node for node number Total per

 

 

or line 10 nodes**
number 6 7 8 9 10 11 12 13 14 15

604-40 2.2 2.3 2.6 3.0 3.7 5.1 5.0 5.4 5.8 6.2 41.332
598-30 2.7 2.8 3.4 3.5 3.9 3.9 4.2 4.8 4.8 4.8 38.8ab
602-30 2.5 3.7 3.4 3.5 3.6 3.7 4.4 4.4 4.4 4.4 38.0abc
598-10 2.8 3.6 3.8 4.1 3.9 3.9 4.0 3.9 4.0 3.7 37.7abc
598-40 3.1 3.3 3.7 3.9 3.8 3.9 3.9 4.1 4.1 3.8 37.6abc
648-30 2.2 2.7 2.9 3.6 2.9 3.8 4.3 4.8 3.6 4.2 35.0bcd
603-50 2.5 2.7 3.1 3.2 3.7 3.6 3.7 3.9 3.6 4.0 34.0bcd
592-40 2.9 2.8 3.2 3.4 3.6 3.5 3.7 3.6 3.4 3.1 33.2cd
608-20 2.7 2.5 2.9 2.9 3.0 3.2 3.4 3.4 3.5 3.6 31.3de
644-20 2.7 2.9 2.6 2.7 3.3 3.6 3.7 3.2 3.3 3.2 31.2de
608-40 1.7 1.9 2.3 2.7 2.8 3.1 2.8 2.9 3.1 2.8 26.1ef
644-30 1.8 1.8 2.2 2.1 2.2 2.2 2.3 2.4 2.9 2.9 22.8fg
607-40 1.4 1.3 2.1 2.2 2.3 2.4 2.7 2.6 2.4 2.8 22.3fg
611-50 2.0 2.0 2.2 2.0 2.2 2.5 2.2 2.0 2.2 2.5 21.8fg
612-30 1.3 1.5 1.9 1.6 1.2 1.8 2.3 1.7 2.2 2.4 17.99
Kora 0.3 0.2 0.5 0.6 0.5 0.7 1.6 1.7 1.8 1.7 9.6h
Pioneer 0.7 0.3 0.6 0.4 0.5 0.5 0.5 0.4 0.6 0.7 5.2hi
Green

Star 0.1 0.4 0.4 0.2 0.1 0.2 0.1 0.4 0.7 0.7 3.3i
Premier 0.1 0.2 0.2 0.1 0.3 0.1 0.3 0.2 0.3 0.3 2.1i

 

**Highly significant difference at 1% level.

zMean separation in column by Duncan's Multiple Range Test, 5% level;
C.V. = 10.9%.

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13

Table 6. Number of pistillate flowers pollinated per plant during a
period of 5 days in a greenhouse experiment with F lines
of pickling cucumbers with multiple-pistillate floéers in
contrast to hybrid varieties with single-pistillate flowers.

 

 

 

 

Variety or Number flowers pollinated per day Total

' **
L1ne Number lst 2nd 3rd 4th 5th flowers
Kora 1.4 1.1 1.6 2.4 3.9 10.4 a2
598-30 1.6 1.3 0.8 1.8 2.1 7.6 ab
648-30 1.6 1.3 1.1 1.4 1.9 7.3 abc
661-50 1.4 0.7 1.8 1.1 2.2 7.2 abc
598-40 1.2 1.2 1.3 1.4 1.5 6.6 bcd
602-30 1.2 0.6 1.1 1.4 1.9 6.2 bcd
608-40 1.3 0.9 0.9 1.1 1.6 5.8 bcd
592-40 1.6 0.9 1.0 0.8 1.4 5.7 bcd
644-30 1.3 0.9 1.0 1.2 1.1 5.5 bcd
608-20 1.4 0.8 1.2 1.1 1.1 5.4 bcd
Green Star 1.5 1.1 1.0 1.1 0.6 5.3 bcd
604-40 1.2 0.9 1.3 1.1 0.7 5.2 bcd
607-4G 1.5 0.7 0.6 1.6 5.1 5.1 bcd
598-1G 1.2 0.6 0.8 0.9 1.2 4.7 bcd
644-20 1.2 0.3 0.7 1.3 1.1 4.6 bcd
612-30 1.2 0.4 0.6 1.2 0.9 4.3 cd
Pioneer 1.2 0.6 0.7 0.7 1.0 4.2 cd
Premier 1.1 0.4 0.7 0.8 0.9 3.9 d
603-50 1.4 0.5 0.4 0.7 0.8 3.8 d

 

**Highly significant differences at 1% level.

zMean separation in column by Duncan's Multiple Range Test, 5% level;
C.V. = 10.91%.

14

although Kora also produced an abundance of pistillate flowers. The
variety Kora produced multiple-pistillate flowers per node, but was
relatively late in this expression as compared to the precocious flower-
ing of the MSU lines. Previous researchers have made the same obser-
vation (13, 21). Under greenhouse conditions Kora performed as a typical
monoecious plant as described by Nitsch (33). At early stages, only
single staminate and occasional pistillate flowers per node were pro-
duced; but at later stages, continuous pistillate flowers were borne.
However, Kora was different in that large numbers of flowers were pro-
duced in a concentrated flowering pattern; i.e., several open flowers
per node per day.

In order to establish the relationship among all these variables,
which may affect yields for once-over harvest, correlation and regres-
sion analyses were performed (Table 7). Strong support was found for
the assumption that large numbers of pistillate flowers might increase
the yield potential for once-over harvest. A highly significant posi-
tive correlation (0.59**) was found between the number of flowers and
the number of fruits per plant (Figure 1). Moreover, the number of
fruits per plant and the weight of these fruits was also highly cor-
related (0.81**) (Figure 2). A multiple regression analysis was done
to define the relationship among the three components of yield (number
and weight of fruits, and number of pistillate flowers). The multiple
regression coefficient was found to be highly significant (R = 0.82**:
Figure 3). The number of flowers and fruits accounted for 66.4% of
the variability in weight (yield) of the fruits per plant. The number
of flowers accounted for 30.2% of the variability in weight of fruits;

whereas, the number of fruits accounted for 65.6% of the variability

15

Table 7. Simple correlation coefficients for yield characteristics of
pickling cucumbers evaluated in a greenhouse and field

 

 

 

 

 

 

experiment.
Characteristics Coefficients of correlation
(1) (2) (3) (4)

Greenhouse Experiment
No. flowers/plant (1) 1.00 0.59** 0.55* 0.08"5
No. fruits/plant (2) 1.0 0.81** 0.22"5
Wt. fruits/plant (3) 1.00 0.13"5
No. pollinated flowers/plant (4) ---
Field Experiment
No. flowers/plant (1) 1.00 0.02"5 -0.35"5 ---
No. fruits/plant (2) 1.00 0.00"5 ---
Wt. fruits/plant (3) 1.00 ---

 

** and * indicate highly and significant differences at 1% and 5% levels,
respectively; ns is nonsignificant at 5% level.

l6

Figure 1. Effect of multiple and single-pistillate flowers per node
on the yield of pickling cucumber.

No. Fruits/ Plant

6.0

5.0

1.0

 

l7

 

r-o.59** A
y=2.12 +0.04x**

1 1 1 1
IO 20 30 40

N0. Pistillate Flowers/ Plant
(From 6 to 15 nodes)

18

Figure 2. Effect of number of fruits set per plant on the weight of
these fruits in pickling cucumber.

19

600 -

300'-

200-

 

Wt.of Fruits (91/ Plant

r =0.8I* *
'00 y =113.37+73.94x**

 

l I l l l l

 

1.0 2.0 3.0 4.0 5.0 6.0
No. Fruits / Plant

20

Figure 3. Partial regression of yield, as weight of fruits per plant
(Y), on number of fruit per plant (X ) versus total regres-
sion where X2 is number pistillate flowers per plant from
10 nodes.

Wt.of Fruits (gll Plant (Y)

480 r-

5
I

8
O
1

360 r-

320 '-

280*-

240 *-

 

200 -
J:

1
1.0

21

X '2.1

  

R-0.82* *
v-114.32+68.35x.+0.64x2*
=0.72* *

08
”2241-041;
. r” -O.81

I -0 55*
"2 ._

l 3 l l L l l
2.0 3.0 4.0 5.0 6.0

No. Fruits/ Plant (XI)

r
yx'at2

f

*-

22

in weight of the fruits per plant. These correlations coincided with
those reported earlier by Hutchins (20), although his correlation co-
efficients were higher than ours. Recently, Smith and Lower (41) found
a correlation of 0.84** between the number of fruits harvested for once-
over harvest and their harvest value which agrees closely with ours.
They concluded that the number of fruits, as correlated to the dollar
value of their size distribution, was the best parameter to estimate
yield of pickling cucumbers for once-over harvest systems. Our data
suggest that breeding for multiple-pistillate flowers per node in gyno-
ecious pickling cucumbers might provide a means for increasing the
number of fruits per plant for once-over mechanical harvest.

All correlations between the number of flowers pollinated during
the 5-day pollination period with number of flowers per plant, number
of fruits, and weight of fruits were nonsignificant at the 5% level
(Table 7). This was probably because of the higher number of flowers
pollinated from Kora (10.4) in relation to the low number of flowers
(9.6), low number of fruits per plant (2.33), and low weight of fruits
per plant (274 9). By observation, Kora produced an abundance of pis-
tillate flowers which increased dramatically with age and time. How-
ever, they were expressed after nodes 6 through 15 were read indicating
an incipient expression of the multiple-flowering character. The cor-
relations were then found significant at the 5% level. Hence, the
large number of pistillate flowers per plant increased the number of
flowers to be pollinated and subsequently the number of fruit set and
resultant yield.

Field experiment. The MSU lines 608-40, 608-20, 648-30, and 598-30

 

were omitted from the field experiment due to a stand loss in these plots.

23

Their results are reported for reference sake (Table 8) since they were

outstanding lines in both greenhouse and field experiments.

Table 8. Number of pistillate flowers per plant for 10 nodes and
number and weight of fruits per plant from 4 MSU lines
omitted from the field experiment due to a stand loss in
field plots.

 

 

 

MSU line no. No. flowers No. fruits Wt. (g) fruits
598-30 32.8 6.60 304
608-20 29.0 7.35 267,
608-40 24.3 5.10 184
648-30 20.5 7.16 405

 

All the MSU lines, selected for multiple-pistillate flowers, pro-
duced as many flowers in the field as in the greenhouse, except MSU
661-50 (Table 9). Accordingly, this genetic character is not adversely
affected by field growing conditions. The MSU lines expressed the
higher pistillate flower counts with up to 39.2 pistillate flowers per
plant from 10 nodes (MSU $98-10); whereas, the commercial hybrids only
produced 9.1 to 14.6 pistillate flowers per plant for 10 nodes.

Although the number of fruits per plant was nonsignificant across
all varieties and lines, there were significant differences between
means (Table 10). However, highly significant differences were found
for the total weight of fruits per plant (Table 10). The correlation
between number and weight of fruits and number of flowers per plant
were nonsignificant (Table 7). Apparently, under field conditions the
commercial hybrids expressed all their hybrid vigor; whereas, the F3

lines with multiple-pistillate flowers were at a competitive disadvantage

24

 

 

 

 

Table 9. Number of pistillate flowers from 10 nodes per plant from a
field experiment with F pickling cucumber lines selected for
multiple-pistillate flowers in contrast to 3 commercial hybrids
with single-pistillate flowers. 3

Variety or Pistillate flowers/node for node number Total per

line no. 10 nodes**

6 7 . 8 9 10 ll' 12 13 14 15

598-10 3.7 3.3 3.8 3.8 4.1 4.2 .43 4.0 4.1 3.9 39.2 a2

603-50 2.8 2.9 2.9 3.3 2.9 3.4 3.9 3.7 3.4 3.6 32.7 b

598-40 2.5 2.8 2.9 3.0 3.3 3.6 3.7 3.4 3.8 3.7 32.7 b

598-20 2.8 3.2 3.2 3.1 3.3 3.1 3.3 3.4 3.4 3.6 32.4 b

602-30 2.2 2.3 2.2 2.8 2.8 3.4 3.1 3.3 3.5 3.3 28.9 bc

592-40 2.3 2.3 2.7 2.6 2.8 3.0 2.9 2.6 3.2 3.3 27.7 bcd

644-20 2.1 2.7 2.3 3.0 2.8 2.6 3.1 2.6 2.8 2.8 27.0 cde

644-30 2.0 1.9 2.0 3.3 3.0 3.1 2.5 2.8 2.6 2.5 25.7 cde

607-40 2.0 2.0 2.3 2.8 2.4 3.2 2.8 2.8 2.7 2.6 25.6 cde

612-3G 1.8 1.8 1.8 1.8 2.1 2.3 2.5 3.0 2.8 3.3 23.2 de

604-4G 1.7 1.3 1.7 2.9 2.4 .23 .25 2.2 2.5 2.9 22.4 e

Kora 1.1 1.2 1.3 1.1 1.3 1.3 1.5 1.4 2.3 2.1 14.6 f

Pioneer 0.9 1.0 1.1 1.0 0.9 0.9 1.1 1.3 1.7 1.1 11.0 fg

Green Star 0.8 0.9 0.9 0.8 0.9 1.1 1.1 1.1 1.0 1.3 9.9 fg

Premier 0.8 1.1 0.8 0.8 0.9 0.9 0.8 1.0 1.0 1.0 9.1 9

661-50 0.7 0.6 0.7 0.6 0.8 0.7 0.8 0.8 0.6 0.5 6.8 g

1

**Highly significant differences at 1% level.

zMean separation in column by Duncan's Multiple Range Test, 5% level;
C.V. = 11.72%.

25

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26

in contrast to the protected greenhouse conditions. In this field experi-
ment, the yield of hybrids may have been favorably influenced by the low
plant density and the environmental conditions during this growing season.
Franken (l3) worked with Kora during 3 continuous years and found that
Kora produced from 0.4 to 2.9 fruits per plant depending on the sowing
date. Pioneer yielded from 0.6 to 2.3 fruits per plant with an average
of 7.1 pistillate flowers per plant counted to 15 nodes (5,37,38). In
our field experiment, Kora produced 7.8 fruits and Pioneer 6.6 fruits
per plant with an average of 11 pistillate flowers per plant.

Our yields were probably higher, on a per plant basis, because of
the low plant population with wider rows and fewer plants per linear
foot of row than plantings for once-over harvest. Notably, the commer-‘
cial hybrids did not yield more than the multiple-pistillate lines even
with their advantage of hybrid vigor. Here again, there is evidence
that breeding for multiple-pistillate flowers per node may provide a
significant potential for increasing fruit-set and yield of hybrid vari-
eties used for once-over mechanical harvest.

Multiple versus single-pistillate flowers. To determine the per-

 

formance of the lines selected for multiple-pistillate flowers, two
types of plants were defined. Multiple-pistillate flowers (MP) are all
those lines which produced an average of two or more pistillate flowers
per node. Lines with single-pistillate flowers (SP) are those lines
with fewer than two pistillate flowers per node. The difference between
means was calculated using t and F test when n1 # 112 (42). From the
greenhouse experiment, the MP plants were significantlyhigher than SP

plants for total number of flowers per plant, number of fruits per plant,

27

and weight of fruits per plant. However, a nonsignificant difference
was noted for the total pollinated flowers per plant (Table 11).
Table 11. Mean comparison test of lines with multiple-pistillate

flowers per node (MP) and lines with a single-pistillate
flower per node (SP) of pickling cucumbers.Z

 

 

 

Flower Yield characteristics

type
No. flowers No. fruits Wt. fruits No. pollinated
per plant per plant per plant (9) flowers/plant

 

Greenhouse Experiment (nMP = 14 and nSP = 5)

MP 32.22 1 6.59** 3.44 1 0.77** 365.71 1 76.48* 5.76 11.10"5
SP 7.62 1 6.41 2.33 1 0.47 288.60 1 55.55 5.62 1 2.72
Field Experiment (nMP = 11 and nSP = 5)

MP 28.87 1 4.98** 5.70 11.16"S 262.73 1 67.04"5 ---
50 10.28 1 2.86 6.50 11.48 304.40 1 76.97 ---

 

2Differences between means were calculated using t and F test when
n f n .
1 2

**and * indicate highly and significantly difference at 1% and 5%
levels, respectively; ns is nonsignificant at 5% level.

From the field experiment, MP plants produced significantly higher
flower numbers than SP plants, although the number and weight of fruits
produced was not different. These results agree with those reported by
Mates (30); i.e., that yield is not necessarily related to number of
pistillate flowers with current hybrids. We suggest that the yield
potential of hybrid varieties for once-aver harvest would likely be
increased by the inclusion of the genetic trait for multiple-pistillate

flowers per node with other necessary traits.

28

Fruit inhibition. A general definition for fruit set is stimula-

 

tion of the ovary to develop into a fruit due to pollination and fertili-
zation (14). Nitsch (33) stated that chemical stimuli may come from
three sources: the vegetative part of the plant, the pollen and/or the
ovules. This general definition does not agree with cucumber fruit set:
because in 1937, Gustafson (16) showed that neither pollination and/nor
fertilization were necessary for cucumber fruit set with parthenocarpic
fruits. Later, parthenocarpic fruiting in cucumber was confirmed by
several researchers (11,33,35). Thus, a new definition for cucumber fruit
set can be proposed sinced growth of the ovary into a fruit is not
always the result of embryo development and resulting seed. Fuller and
Leopold (14) defined fruit set as follows: the condition in the cucum-
ber ovary when it has received the signal from the plant itself to en-
large and develop into a fruit. This "fruit signal" is likely a plant
hormone. Auxins, gibberellins and cytokinins have been shown to stimu-
late ovary development into a fruit (12,18,33). More0ver, auxin acti-
vity was found in pollen and in developing seeds (2,11,16,22,23,31,33).
Earlier, Tupy and Ranganamy (43) suggested that the fruit set signal
could be derived from other classes of compounds such as nucleic acids.
Recently, Fuller and Leopold (15) demonstrated that "new" nucleic acid
(RNA) synthesis is necessary for cucumber fruit growth which occurred
within 9 hours after pollination.

The actual mechanism for cucumber fruit set is unknown; neither
is the means of fruit inhibition by first-set fruit known. From our
greenhouse experiment, the percentage of fruit inhibition for each
pollination day in a comparison of MP with SP lines was made (Table 12).

From both groups of plants, 1741 flowers were pollinated during the 5

29

Table 12. Comparison of pickling cucumber with multiple-pistillate
and single-pistillate flowers per node for percentage of
fruit inhibition for each pollination day; greenhouse

 

 

 

 

experiment.
Pollination Total Total Fruit ’ Fruit Total wt.
day number pollinated fruits inhibition set fruits
flowers
(no.) (no.) m (74) (9)
Multiple and single-pistillate flowers per node (305 plants)
1 409 374 8.56 91.44 66975
2 249 207 16.87 83.13 23137
3 291 162 44.3 55.67 10654
4 354 130 63.28 36.72 4959
5 358 101 71.79 28.21 2658
Total 1741 974 44.06 55.94 108563

Multip1g1pistillate flowers per node (221 plants)

 

1 308
2 191
3 218
4 257
5 318
Total 1292

285
169
143
107

86
790

 

7.47
11.52
34.40
58.37
72.96
38.85

11.88
34.48
73.97
76.29
87.50
78.84

92.53 51429
88.48 19870

65.60 9752
41.63 3649
27.04 1624

61.15 86324

88.12 15546

65.52 3447
26.03 902
23.71 1310
12.50 1034

21.16 22239

 

30

days and only 974 flowers set fruits or 44% fruit inhibition. The MP
plants exhibited 39% fruit inhibition, whereas SP lines exhibited 79%
fruit inhibition (Table 12 and Figure 4). Thus, the MP lines with gene-
tic potential for multiple-pistillate flowers per node, which both in-
creases the number of flowers to be pollinated and decreases the per-
centage first-fruit inhibition, subsequently produced more fruits per
plant for the once-over harvest.

Our findings of fruit inhibition agree with those reported (7,26),
but the mechanism for fruit inhibition is still unknown. Possibly, the
same auxins responsible for fruit growth are also the chemical agents
or signals which cause the inhibitory effect. There is some evidence
that auxin transport inhibitors stimulate fruit set (3,4,5,6). Again,
the question of source of auxin synthesis and mechanism for auxin trans-
port in relation to fruit inhibition has not been adequately answered.
Muir (31) determined that the endogenous auxins of pollen grains is
insufficient to stimulate fruit set. It has been shown that the pollen
tubes secrete an enzyme which synthesize auxin from tryptophane, the
suggested precursor for indole-3-acetic acid (IAA;33), in the style,
which subsequently stimulates ovary growth. Fuller and Leopold (14)
found that fruit set occurred within 18 hours after pollination, but
fertilization occurred 30 to 36 hours after pollination. Hence, pollina-
tion was a requirement for fruit set, but fertilization may not be
required which corroborated the suggestion of Muir (31).

The possibility that ethylene plays a role in cucumber fruit inhi-
bition has not been mentioned in the literature. The decrease in auxin

content of the ovary shortly before anthesis may be signaled by ethylene.

Figure 4.

31

Percentages of fruit inhibition (—-—) and fruit set (---) in
the cucumber plant during a 5-day pollination period (MP is
multiple-pistillate flowers and SP is single—pistillate flowers
per node). The correlations of r = 0.98 are significantly
different at the 1% level and r = 0.94 are significantly dif-
ferent at the 5% level.

 

°/o Fruit Inhibition

l00

N|
0|

0|
0

25

 

32

 

 

 

Time (Days)

I00

5.
01

01
0

°/. Fruit Set ---—-

N
01

33

High auxin concentrations stimulate ethylene synthesis (2); and con-
versely, high ethylene concentrations lower the level of auxin and
inhibit auxin transport (2,22). Furthermore, very high auxin concen-
trations may make tissues insensitive to ethylene. We speculate that
fruit inhibition occurs as follows: shortly before anthesis the de-
crease in auxin concentration is caused by ethylene production which
blocks fruit growth. Then, at pollination, the pollen carrying the
enzyme stimulates new auxin synthesis for fruit set which occurs within
18 hours of pollination (14). During this period, due to high auxin
concentration, the ovary tissues become insensitive to ethylene, but
ethylene production continues due to new auxin synthesis and its
capacity for autocatalysis (2). Now, a large source of hormone which
can be translocated throughout the plant inhibits (1) cell division

or enlargement, (2) DNA synthesis, and (3) meristematic division of
roots, shoots and auxillary buds, but without influencing RNA synthesis
(2,22) is available from the "first-set" developing ovary.

This coincides with the results of Fuller and Leopold (15) regard-
ing the necessity for RNA synthesis for fruit set. The inhibitory effect
is removed by fruit harvest or maturation until a new fruit is set: and
then, the inhibitory cycle is repeated. This agrees with our findings
on fruit inhibition and those reported by Collison and Martin (7).
Fruit inhibition occurred within 24 hours of pollination in our experi-
ments, which coincided with the time for fruit set after pollination,
18 hours (15). Furthermore, fruit inhibition increased dramatically
within 48 hours of pollination, which is the time required for fertiliza-

tion and resultant higher auxin production rates and accumulation. This

34

hypothesis might help explain the mechanism responsible for the con-
trast between the auxin content of the ovary before and shortly after
pollination. More importantly, it could explain the well-known "first-
fruit“ inhibition effect so prevalent in cucumber plants. This idea

merits further research regarding its validity.

CONCLUSION

Lines of pickling cucumber with multiple-pistillate flowers per
node provide a significant potential for the development of new pickling
cucumber hybrids for once-over harvest. The increased numbers of flowers
per plant increases the number of flowers available for pollination
which subsequently increases the number of fruits per plant by decreas-
ing the percentage of fruit inhibition. There are more pistillate
flowers per plant per day resulting in more possible pollinations with
a more concentrated fruit set. This circumvents a portion of the "first-
set" fruit inhibition, and produces more fruits per plant or yield for

once-over mechanical harvest systems.

35

LITERATURE CITED

Baker, L.R., J. Rudich, J.W. Soctt, and J. E. Wilson. 1975.
Pickling cucumber breeding research. 1N; Pickle Research at
Michigan State University-l973-1974. Mich. Agr. Expt. Sta. Res.
Rpt. 277.
Burg, S.P. 1973. Ethylene in plant growth. Proc. Nat. Acad.
Sci. 70:591-597.
Cantliffe, D.J. 1974. Promotion of fruit set and reduction of
seed number in pollinated fruit of cucumber by chlorflurenol.
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1974. Sex expression in cucumbers. Min. Agr. and
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., and S. C. Phatak. 1975. Use of ethephon and chlor-
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1977. The induction of fruit set in cucumbers by chlor-
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inhibition with optimum pollination conditions. 1N: Pickle
Research at Michigan State University-l975-1976. Mich. Agr. Sta.
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36

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37

Cunninghan, C. R. 1940. Fruit setting of watermelons. Proc.

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Denna, D. W. 1973. Effects of genetic parthenocarpy and gynoecious
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Cucumis sativus. L., J. Amer. Soc. Hort. Sci. 98:602-604.

 

Elassar, 0., J. Rudich, D. Palevitch, and N. Kedar. 1974. Induc-
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1977. The role of nucleic acid synthesis in cucumber
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1939. The cause of natural parthenocarpy. Amer. J.
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1939. Auxin distribution in fruits and its significance
in fruit development. Amer. J. Bot. 26:189-194.
Hibbard, A. D. 1940. Fruit thinning the watermelon. Proc. Amer.
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38

Jensen, J. L. 1969. Eengangshost i drueagurker (Once-over harvest
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Key, J. L. 1969. Hormones and nucleic acid metabolism. Ann.
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Laibach, F. 1933. Pollen hormon und Wuchsstoff. Ber. Dtsch. Bot.
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Martin, E. C., and C. Collison. 1975. Honey bee activity in pick-
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McCollum, J. P. 1974. Vegetative and reporductive responses
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