Source sink relationships in the cucumber plant (Cucumis sativus) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Science at Massey University

SOURCE- SINK RELATIONSHIPS

IN THE CUCUMBER PLANT (Cucumis sativus L.)

A thesis presented in partial fulfilment of the requirements for the degree or

Master of Science in

P J an t Sci c n c e at

Massey University

Chapter

1 • 1 1 • I • 1

1. 1. 2

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2. 1

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Abstract.

Acknowledg~ents .

List of Tables.

List of Figures.

Introduction.

Review of Literature - The cucumber plant.

The young cucumber plant.

Contribution of cotyledons and leaves

to gro1>1th.

Factors influencing Lhe growth of the young cucumber plant.

Sex expression.

Types of sex expression.

Sex differentiation of flowers .

Factors influencing sex expression. Summary.

Fruit set.

Fertilised fruit .

Parthenocarpic fruit

_,,

Review of Literature - Source- sink r elationships.

Termi·nology.

Sink strength.

Page vii x xi xv xvi 2 8 8 9 10 1 6 1 6

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Chapter

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2. 2. 1

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Sink or source limitation.

Sink strength and the photosyntheLic

rate .

E.f.fect on the photosynL11cLic raLc.

Control mechanism.

Source or sink limitation.

Change with selection.

Identifying limitation.

Summary.

The c.f.fect of two auxin transport

inh.ibl tors on growtl1 and

development.

Introduction.

Materials and methods.

Hesults.

InLroduction.

Total planL dry weight and dry wci~1L

of component organs.

Partitioning of' dry weight.

Fruit set.

Fruit size.

Distribution of fruit dry weight on

various nodes.

Misshapen fruit.

Discussion.

Dry weight of component organs and

partitioning between them.

Fruit data.

i i i

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Effect of growth substance.

Relationship between stage of flower development and fruit set.

Summary.

The effect of leaf removal on growth and development.

Introduction.

Materials and methods.

Results.

Introduction,

Number of nodes per plant, total plant

dry weight and dry weight of compo -nent organs.

Number and mean dry weigl1 t of fruit .

Partitioning of the dry weight between

the component organs.

Fruit data.

Sex expression.

Discussion.

Dry weight and partitioning of the dry

weight between the component organs.

Fruit data.

Influence of leaf removal treatments on the sex expression.

Conclusion.

Chapter

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Materials and methods.

Results.

Introduction.

Dry weight and partitioning.

Absolute growth and partitioning of this growth over period two .

Fruit data.

Discussion.

Dry weight and partitioning of the dry weight,

Distribution of fruit dry weighL on

various nodes. Conclusion.

The effect of carbon dioxide enrichment

on growth and development.

Introduction.

Materials and methods.

Results.

Introduction.

Absolute growth rate.

Partitioning of the absolute growth .

Fruit data. Leaf data.

Stem data.

Redistribution of assimilates.

Discussion.

Absolute growth rate and partitioning.

Chapter

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Fruit data.

Leaf data.

Summary.

Source- sink relationships in the

Cucumber plant.

Partitioning of dry weight.

Source or sink limitation.

Fruit set.

Distribution of fruit growth on various

nodes.

Conclusion.

Appendices.

Bibliography.

Page

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123

125

ABSTRACT

In an attempt to increase the sink strength of the

fruit , two auxin transport inhibitors were sprayed on

to the whole plant or applied to the fruit , four days

after first anthesis. Application to the plant

i ncreased fruit set , reduced the dry weight of all the

component organs, but had l i t t l e effect on the

partitioning of the dry weight. With application to

the fruit chlorflurenol had l i t t l e effect, but TIBA at

200 ppm reduced fruit set on the lower nodes where _i_ t

was applied. This reduction in fruit set r educed

fruit dry weight and partitioning to the fruit.

As neither o1 these grO\vLlL ~ulJsLan es increa~ccl

sink strength i t was decided to investigate source sink

relationships by altering the source strength. With

increasing degree of leaf removal total plant dry

weight was reduced but the parLitioning was l i t t l e

affected. However with the severest leaf removal

treatment a greater proportion was partitioned into

the stem and less into the fruit , but the proportion

partitioned into the l eaves was not altered.

Deleafing as a method of reducing source strength

has been criticised due to i t s effect on the distribu

-tion of hormones. For this reason the effect of

shading was investigated. The partitioning of the

sized fruit was not affected by up to

58%

However with an increase in shading from

58%

70%

the partitioning to the :fruit was reduced. Below a

critical level of assimilate supply the competitive

ability o:f the vegetative organs seemed to be higher

than tlle :fruit.

As delea:fing and shading reduced source strength

the e:f:fect of increasing source strength by carbon

dioxide enrichment was investigated. Enrichment was

applied from :first anthesis and increased the growth

rate of the plant in the following five weeks. The

partitioning was not differenL to the control plants

in the first week folloHing anthesit:>. However in week

bvo the partition i_ng to -Lhe fruit was less wi tlt enr_i.ch

-ment. There appeared to be an accwnulaLion of assirni

-lates jn the leaves due Lo -Lile mo hi LisinG ahi 1 i ty of the

growing regions being i11sufficienL .for Lhc hie;lter raLe

of assimilation. In week three and four the mobilising

ability of the growing regions increased and there

appeared to be a redistribution of stored assimilates as

there was a loss o.f l eaf and petiole dry weight. The

accumulation of assimilates inhibited the NAR but

:following the redistribution o:f stored assimilates the

NAR recovered. In the :fifth week the partitioning was

very similar with or without enrichment, and these

partitioning :figures were very similar to that obtained

ix

experiment. I t appears that once the plant develops

several medium sized fruit i t partitions about 70% of

the absolute growth into the fruit,

2J%

6%

1%

range of assimilation rates.

With higher raLes of assimilation l'ruit set and

fruit size increased. This cuJ l i var has many po Len ti al

fruit si tes as i t produces few rna·1 c flowers and o.ften

several flowers per node. With greater raLes of'

assimilation fruit set will increase and should be

capable of utilising L.hc greater supply.

the plant appears to 1.Jc s ourc t~ l i..mj_ t t!cl.

Grateful acknowledgements are made to Dr K.J . Fisher

and Dr D.J . Woolley for their encouragement and guidance

in this project. I would also like to acknowledge the

assistance given by Dr D.R.K. llarcllng, L. Gould and

F. Anderson in harves ting the plants, and H.M. Gordon who

typed this thesis . Finally I would like to thank my

wife , El 1 ie , and 111y t wo daugh tc re;, Fri tlta and Morwenna,

for their encouragement and patience whilst I completed

Table

3

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3.2

3

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3

3

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4

3

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5

3

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6

3

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7

3,8

3

,

9

3

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3

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3

.

LIST OF TABLES

The treatments.

Effect of site of application on fruit

dry weight (g/pl).

Interaction between site of application

and rate on total plant dry weight

and weight of component organs (g/pl).

Effect of growth substance on fruit and

stem dry weight (g/pl) .

Effect of site of application on percent

total dry weight in roots

₍

_%

_{) •}

Effect of growth substance on percent

total dry weight in fruit, leaves and

st em (

%

)

•

Interaction between growth substance and

site of application on percent

total dry weight in leaves (%).

Interaction between site

or

and rate on percent

weight in stem(%) .

total dry

Interactions between site and rate, and

site and growth substance on fruit

set on nodes 1- 8.

Effect of treatments on fruit set on

nodes

3

-

5

.

Effect of treatments on fruit set on

nodes

6-8

.

Effect of treatments on the fruit set

on nodes

9

-

16

.

Page

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50

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54

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Table

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14

3

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5

3

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6

4

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4

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2

4

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3

4

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4

4

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5

4

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6

4

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7

4

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8

5

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Effect of site of application on mean

fruit dry weight (g).

Percent total fruit dry ,.,reigh t on

nodes

1-

8

9-16

(

%)

.

Effect of treatments on percent

total fruit dry weight on nodes

3

-

5

and nodes

6-

8

(%)

.

Percent fruit dry weight that was

in misshapen fruit.

Leaf removal treatments.

Effects of treatments on number of nodes,

total plant dry weight and dry we.ight

of component organs (g/pl) .

Number and mean dry weight of fruit with

various leaf removal treatments (per

plant) .

Percent total dry wci~1t in the

component organs

(%

)

.

Association between a fruit and a node

with a leaf.

Distribution of fruit dry weight on the

various nodes

(%)

.

Effect of treatments on fruit numbers

on various nodes (per plant).

Number of nodes with male flowers, on

various nodes numbered from the

base of the plant.

Mean dry weight of the leaves with the

different shading treatments (g/

plant).

Page

57

58

59

69

70

71

72

73

74

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Table

5

,

2

5

,

3

5

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4

5

,

5

5

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6

5

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7

5

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8

5.9

5

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6

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6

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2

6

.

3

6

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4

6

,

5

Mean dry weight of the leaves at the

two harvests (g/plant) .

Significant interactions on the dry

weight of the component organs

(g/plant).

Percent dry weight in the roots with the various shading treatments .

Percent dry weight in the roots at the two harvests.

Significant interactions on percent

dry weight in the component organs.

The absolute growth between Ill and H2

and the partitioning of this between the component organs.

Effect of shading on fruit set.

Percentage of fruit dry weight on

various nodes

(%

).

Distribution of the absolute fruit

growth over period two on the

various nodes

(

%

).

Absolute growth rate of total plant and

t r (g.pl -1 . day -1).

componen o gans

Partitioning of the absolute growth

(%

).

Relative growth rate of the fruit.

Per cent absolute fruit growth in week

5

Number and mean dry weight of fruit at

harvest six.

Table

6

.

6

6.7

6

.

8

6

.

9

6

.

Dry weight and per cent total fruit dry

weight in aborted fruit at liarves t

six.

Leaf area and number of l eaves per

plant.

Leaf area of individual l eaves at

harvest six (cm2/plant) .

Net assimilation rate (g/m2/day).

Stem length and stem weight per length

for each harvest .

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107

Figure

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5

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6

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6

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4

LIST OF FIGURES

Stage of flower development at t ime of

growth substance application.

Partitioning of dry weight with the leaf

removal treatments.

Dry weight of component organs at two

harvests and with different

shading treatments.

Per cent absolute growth partitioned into

fruit and leaves in each week.

Per cent absolute growth partitioned into

petioles, stem and roots in each

week.

Distribution of aborted fruit dry weight

at harvest six.

Net assimilation rate in each week.

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86

100-101

101-102

10J-1 0 Li