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THE INFLUETCE 0F DEFOLIATION AND FRUIT 'IHINNING
(N THE GROWTH OF TOMATOIS

BY

ALTCN MILLETI' PORTER

A Thesis

submitted to the faculty of the Michigan State
College of Agriculture and Applied science in partial
fulfillment of the requirements for the dogma of
Master of Science

Department of Horticulture

East Lansing, Michigan

1938

THESig

ACKNOWIEDW T8

The writer wishes to express appreciation for the assist-
ance of Professor V. R. Gardner for the original planning and
developing of the investigation and for constructive criticism
of the manuscript; to Professor H. L. Seaton for assistance
in planning and carrying on the work; to Professor W. 0. Dutton
for his help in making the photographs and to Professor F. 0.
Bradford, Dr. C. H. Mahoney and Dr. I. W. Grist for the many
helpful suggestions and criticians in connection with the work

and writing the manuscript.

’TABLE OF CONTENTS

Introduction ....................................
Review of Literature ............................
Objectives ......................................
Methods .........................................
Results

Foliage Growth ................................

Fruit Growth ..................................
Discussion ......................................
summary .
Bibliography ....................................

App.nd1x .0.0.0....OOOOOOOOOOOOOOOOOOOO0.0.0.0...

Page

12

16

30
31

33

INTRODUCTICN

The tomato is probably grown under a greater diversity of
conditions than any oiher vegetable crop. Furthermore, it is sub-
mitted to a greater variety of cultural treatments. It is but
natural that it should show widely varying responses to those re-
spective conditions and treatments. There is very little information,
though obviously the matter is of fundamental importance, as to the
mount of foliage that is required under different conditions for the
developing and maturing of a given quantity of fruit. Unless there
is some answer to this question, such practices as pruning, dis-
budding and fruit thinning cannot be employed understandingly.

Review of Literature

The advantages claimed for pruning tomatoes (Stuckey l3),
(Olney 11), (Lloyd and Brooks 5), (Rose 12) are: (a) earlier ripen-
ing, (b) larger fruits, (c) less disease, (d) larger yields, (e)
cleaner fruit, (f) more convenient harvesting and (g) more effective
spraying of the plants. The disadvantages are: (a) greater mount
of labor and expense, (b) less total yield, (c) greater loss from
blossan and rot, (d) more sunscald on the fruit and (a) a greater
mount of cracking of the fruits. sue of these claimed advantages
are more or less the Opposite of the claimd disadvantages. The
pruning of tomatoes increased the quality and size of ripe tomatoes
according to Whipple and Schemerhorn (16), olney (11) and Stuckey
(13), but Lloyd and Brooks (5) found a very sligit, if any, effect
on the size of tomatoes from pruning. The yields of tomatoes were

reduced about one third by pruning according to Stuckey (l3),

Olney (11), Lloyd and Brooks (5), Rose (12), Whipple and
Schemerhorn (l6) and Hoffman (4).

The rate of food manufacture by the leaves of the plant
is determined by the rate of photosynthesis. This in turn is
influenced by the length of day or light intensity, according to
Tincker (15). The factors that govern the effect of light on the
tomato leaves are: (a) intensity of light, (b) quality of the
wave length of radiation and (c) duration of the eXposure (3).

Magness and Heller (7) found that the maximum size was
reached in apples when they had forty leaves per fruit. It de-
creased when there were more or less than forty leaves per fruit.
They found that the fruits with a large leaf area had a higher
percentage of dry weight and ripened earlier than the fruits with
a relatively small leaf area.

Winkler (17) working with grapes under the same light
conditions for all the vines found that about sixteen leaves were
required for the best development of size and quality of about
forty berries. Increasing or decreasing this leaf area per forty
berries reduced the size and quality of the berry.

Magness and Overlay (6) working with Qples and pears
found the amount of leaf surface necessary to synthesize the or-
ganic foods utilized in the developnent of apples and peers.

They explained the decrease in fruit volume as partly due to the
greater concentration of carbohydrates in fruit growth with
larger leaf area. There is a possibility that a greater accumula-

tion of synthesized materials when a large leaf area is available

3.

tends to inhibit synthesis of organic fOOds in the leaves.

In Murneek's (10) experimental wcrk on tomatoes careful
observations were made for the purpose of finding the effects of
fruiting on vegetative growth of both nitrogen-high and nitrogen-
low plants. By defruiting plants grown during long-or short-day
periods he found the foliage became darker in color, grew rapidly
and the stms were larger and more firm than in normally fruiting
plants. The long-day plants increased in heighth 13 to 20 per
cent faster than the short-day plants. The developing of fruit
on the normal and vegetative growth on the defruited short-day
plants was leading;to rapid exhaustion of the stored carbohydrates
because the current synthesis was inadequate. Under such circum-
stances the carbohydrates would act as limiting factors in the
normal development of the fruits. In every case a maximum crop
of fruit had a strikingly retarding effect on the vegetative
growth and development of the plant, but it was not as rapid on
the defoliated plants. The less fruit that was permitted to
develOp the more the leaves, stem and fruit grew. The height
growth of’the plant declines in prOportion to the amount of fruit
set.

MacDougal (8) in Arizona feund that cloudy weather caused a
uniformly high rate of growth in foliage and fruit of the tanato,
and that high temperatures did.not accelerate growth unless they
were accompanied with high relative humidity. This showed that
there must be a balance between the water supply and transpiration

of a highly succulent fruit to produce an increase in its volume.

North
F C H
G D A
H E B
A F C
B G D
C H E
D ‘L P
E B G
Figure I.

Arrangement of’plants in the

1 leaf par fruit E
2 leaves per fruit F
3 leaves per fruit G
4 leaves par fruit H

plOte

- 5 leaves per fruit

6 leaves per fruit

7 leaves per fruit

Check plants

4.

leaf area in square centimeters.

5.

527 .
496 . .
465 .
434 ,
403 . .
372 .
341 - ' '

310 »

2'79 . .

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186
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2.5 5 7.5 1012.5 1517.5 20 22.5 25 27.5 30 32.5 55 37.54
Length

Figure 2. Showing relation between leaf area and length
from basal leaflet to tip of leaf.

 

6.

The rate at which the water is received is so little in excess of

transpiration that a rise of 10 - 15°C may destroy the balance and

stop fruit growth.

Objectives

The object of this investigation was to throw some light on
the following questions:

1. The effects of defoliating and fruit thinning on the rate
of tomato growth and total size of matured fruits.

2. The effects of defoliating and fruit thinning on the per-
centage of dry matter in the plants and fruits.

3. The difference between the leaf area required in the
winter'months to develop a certain quantity of fruit and that re-
quired by the same variety in the spring or summer under different
light conditions.

Methods

tnt the outset it was necessary to devise a method of measur-
ing leaf area. This method was developed from the correlation be-
tween the area and length of the leaf measured fronxthe first basal
leaflet to the tip. This correlation was found by taking one hundred
thirty-four tomato leaves at random.and outlining each on paper.
These tracings were the: measured with a planimeter to find the exact
area of each leaf in square centimeters. The area of each of these
leaves was then plotted against the length. (Figure 2). The equation

for fitting a line to (Figure 2) was found to be y = -3.l6+»4.l7x +

.30712. The correlation between area and length was found to be

7.

Table 1. The number of leaves and fruits on the treated plants.

Average Average Total fruits

Plants leaves per fruits per per lot of‘plants
fruit plant
Fall Spring Fall Spring
A, 1 2.7 2.2 16 13
B 2 2.5 2.7 l5 16
c 3 2.8 8.3 17 14
D 4 2.3 2.0 14 12
E 5 2.0 2.0 '12 12
F 6 1.8 2.0 11 12
G 7 1.7 1.5 10 9

Table 2. The number of leaves and fruits on the check plants.

Average Average Tbtal fruits
Week leaves per fruits per per lot of plants
fruit plant
Fall Spring Fall Spring Fall Spring
1 8.5 10 2 1.2 12 6
2 4.8 7.5 3.8 2.0 23 10
3 4.0 2.9 5.5 5.8 33 29
4 2.7 1.8 9.0 9.8 54 49
5 2.2 1.4 12.1 13.2 73 66
6 2.1 1.5 13.0 13.8 78 69

7 2.1 1.5 13.8 14.4 83 72

.968 1' .0018. Accordingly length was used as the unit of measure-
ment from.which leaf area was canputed. Length measurements were
taken every seven days.

In order to control conditions as much as possible the ex-
perimental studies were made in the greenhouse, one crop being
started at such a time that flower and fruit development took place
during the short cloudy days of’November'end December; another crop
was started at such a time that flower and fruit development took
place during the long sunny days of April and May.

The Grand Rapids Fbrcing variety of tomatoes was used. The
plants were trained to a single stem and grown two feet apart each
way in a loam.soil that was treated in the fall with 0-20-20 com»
mercial fertilizer at the rate of 1500 lbs. per acre. These plants
were watered by an overhead sprinkling system, except during the
cloudy weather in the fall when a hose was used so as not to spread
leaf diseases. There were no insect or disease attacks during the
experiment to interfere with the progress of the work.

The fall crop was defoliated and defruited on.November 21,
1931; the spring crap on llmrch 20, 1932, and measurements of the
leaf areas were taken every seven days for seven weeks in each case.
The various lots of plants were set in the plot, as illustrated
in figure 1 and all plants were defoliated and defruited, as shown
in table 1. In table 2 is illustrated the natural deve10pment of
the check plants. ‘All the leaves were measured and their areas

computed every seven days by the use of the equation developed for

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measuring leaf area. The volune of the fruit was found every
seven days by the water displacement method. This consisted in
putting water in a cylinder calibrated in cubic centimeters and
placing the tomato in it to find the number of cubic centimeters
of water displaced.

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of charing the absorbed and reflected energy. This was done by
recording the difference every two hours between the readings on
a black centigrade and a standard centigrade thermometer. (Table
12.)

‘lhe sunshine data were obtained from the United States
Weather Bureau at East Lansing. (Table 12).

The methods used to determine the percentages dry matter in

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plants and fruits was by drying than in an oven at 90 C for 48 hours.

Results
Foliage growth.

Both the fall and spring plants showed a rapid rate of
foliage growth following either defoliation or defruiting. This
rate decreased each week on all the plants except the F and G lots,
where it increased for three weeks and then decreased the last four,
and the H lot where it remained rather constant. As the leaves be-
cmne more mature the total leaf area per tomato did not increase as
rapidly except on the check plants where young leaves were contin-
ually forming and older ones maturing more rapidly than on the de-

foliated and defruited plmts. (Tables 3, 4 and Figure 3).

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The removal of the leaves had a stimulating effect on the
rate of growth of all the plants, and the more foliage was re-
moved the greater was the stimulus. (Tables 3 and 5). The leaves
on the defoliated plants developed to much greater size and were
much darker in color in both crops than they were on the check
lot of plants. The leaves on the defoliated plants of the spring
crop developed severe curling, but this did not seem to affect the
foliage or fruit growth. (This is illustrated by the plates in
the appendix.) since the check plants did not develOp this curling,
it was believed to be due to the defoliating and defruiting of the
plants. The increase in leaf area after defoliating or defruiting
or both was much greater on the spring than on the fall plants, and
this is true when figured either in tenns of absolute area increase
week by week or in terms of percentage increase. The percentage
increase in leaf area week by week did not seem to be influenced
materially by the number of leaves per fruit. That is, the per-
centage increase in leaf area was Just about the same for a one-

leaf-per-fruit plant as for a five-leafbper-fruit plant.

Fruit growth.
The rate of fruit volume increase are presented in data
on table 7. These show that the fruits in the fall reached their
peak of volume increase one week later than those of the spring
crop although the fruits on the spring plants were actually gaining
in absolute weight faster throughout the entire growing period.

The fall crop had a small increase in size just before maturity and

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21.

the fruits ripened very slowly, while in the spring the tomatoes
increased in volume right up to maturity and ripened rapidly. All
the fruits produced on the defoliated and defruited plants made a
much larger size and matured earlier than the fruits on the check
plants. (Table 10 and Figure 4).

In table 8 it will be noted that the plants with a large
amount of foliage have a more constant increase, (on the percentage
increase scale) of fruit over the period of seven weeks than any of
the other plants considered in the experiment. The fruits on the
E and F'plants increased much more rapidly and reached a larger size
on the fall crop than any of the other plants. on the spring crop
the fruits on all the plants defoliated and defruited were larger
than the maximun sized fruits on any of the fall crop, but the fruits
an the A, B, and 0 plants were much larger than on any of the other
plants. The fruits on the G plants were smaller than others on both
crops. The fruits on the check:plants did not grow large and they
ripened at about one-third the size of those on the other plants.
They were slow in growing 81d maturing, and due to the large number
of fruits in a cluster and the small amount of leaf area per fruit
they were small. (Tables 7, 8 and 10).

There was a steady rise in the rate of increase of fruit
volume per unit of leaf area from the beginning to the and or the
seven week period. This took place in both the fall and spring
crop and is especially noteworthy in connection with the fall crep,

for the period during which that crop was developing was characterized

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by a steadily decreasing light intensity and an even more striking-

 

ly decreasing percentage of sunlight. This would seem to indicate
either that (1) during the latter part of the period of deve10pment
of the fruit when the fruits were growing most rapidly the leaves
were functioning more efficiently, or (2) that during this same
period the fruits were able to obtain a larger percentage of the
products of photosynthesis. That this latter hypothesis is closer
to the condition that actually existed is indicated by the fact
that during this period of relatively slow growth of the fruits the
leaf area was increasing rapidly, while later when the fruits were
growing the more rapidly the leaves were growing but little. It

is also significant that the volume of fruit per unit of leaf area,
and likewise the increase in volune of fruit per unit of leaf area,
was essentially the same in the fall as in the spring. The spring
crop apparently should have a greater absolute increase in fruit
size and fruit development fran week to week then the fall crop
because the plants developed larger leaves in the spring. The
fact that maximum amount of fruit was produced by the unpruned and
unthinned plants (table 11) and that the volume increase per unit
of leaf area each week was greatest on these same plants in the
case of both fall and spring crops indicate that fran the stand-
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efficient when there is a very limited leaf area per individual fruit.
on the other hand, when too many fruits set and start to develop for
the leaf area possessed by the plant; the individual fruits are

unable to attain commercial size. Therefore, some fruit thinning is

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advisable, butJmore than enough to insure the minimum size or
sizes that are satisfactory commercially is reasonably certain
to reduce the efficiency of the plants.

The light intensity and per cent of sunlight are shown
in table 12. The fruits do not ripen as evenly during the dark
cloudy days of low light intensity in the fall as they do during
the longer days of a higher light intensity in the spring.

The dry matter content of the tomatoes on the plants of
different treatments is presented in table 13. It seems that the
larger the tomato develops in size the more concentrated the
nutrient material in the tomato becomes.

The foliage, stuns and fruits of the fall crop have a lower

percentage of dry matter than is true of the spring crop. (Table 13).

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DISCUSSION

In tomato growing under glass it is generally considered
that tanato plants maturing their fruit during the long brighter
days of spring will set fruits more freely and they will grow to
larger size than plants maturing their fruit during the shorter
duller days of late fall and early winter. The differences in
light intensity and percentage of sunshine correspond closely with
the above differences. This variation in light supply may be the
cause of the efficiency of the foliage per unit area, but it de-
pends more on the total anount of foliage possessed by the plant
at any time. This is indicated by the close correlation between
rate and amount of fruit developnent and rate and amount of leaf
development. From this information it seems that there must be a
seasonal balance between the fruit number and leaf area in order
to get maximun production of relatively large sized fruit. In
the fall or early winter months of dull days and low light intensity
it is evidently necessary to have a larger number of leaves per
fruit than in the brighter days of late winter and early surmner.
When the fruit sets sparingly, this balance can be brought about
by defoliating or pruning, but when the fruits set heavi ly, the
proper balance can be more easily brought about by defruiting or
fruit thinning.

The evidence presented also indicates that there must be a
fairly definite ratio between leaf area and number of developing

fruits in order to have most efficient foliage and maximum develop-

.ment of fruit of good size. This ratio will vary somewhat with
different varieties, size of leaves and size of fruits that are
desired.

The data presented suggests why directly opposite results

were found in some of the investigations on pruning of tomatoes,

cited in the Review of Literature.

SUMMARY

1. When various amounts of defoliating and defruiting were
practiced, there was a distinct difference in rate of foliage and
fruit growth and in total foliage and fruit growth.

a. The season of the year had a direct effect on the rates
and totals in foliage and fruit growth. The light intensity and
length of day had the greatest influence on this direct effect on
the plants grown in the fall or early winter and late spring or
early summer.

3. It was indicated that when the preper balance between
leaf area and fruit volume was reached, the fruits developed more
rapidly and became of a larger size than otherwise.

4. The percentages dry matter in the fruits and plants is
regulated by the anounts of foliage developed and sunlight re-
ceived in both crops.

5. It is evident that the light intensity'and amount of
sunlight had a greater effect on the growth of foliage and fruits

than any other factor considered in the growth of a crop of tomatoes.

l.

3.

4.

5.

6.

7.

9.

11.

12.

13.

14.

BIBLIOGRAPHY

auchter, E. 0. Md. Agr. mp. Sta. Bull. 257 (1923)

Bailey, L. H. and W. M. Munson, Tomatoes, Cornell Univ.
,Agr. Expe Stae Bulle 21 (1890)e

Garner, w. W. and H. a. Allard, Effect of Relative Length
of Day and Night and other Factors of Environment on
Growth and Reproduction in Plants. Jour. Agr. Res.
XVIII pp. 553.

Hoffman, I. 0. Effect of loaf Pruning upon the Yield of
Greenhouse Tomatoes. Proc. anor. Soc. Hort. Sci.
pp. 360-363, 1930.

Lloyd, John W. and I. 8. Brooks, Growing Tomatoes for
Early Market, 111. Agr. Exp. Sta. Bull. 144 (1910).

Megness, J’. R. and F. L. Overlay, Relation of Leaf Area to
size and Quality of Apples (1929). and Pears. Amer. Soc.
Harte 8010, ppe 160-163e

Magiess, I. R. and M. H. Heller, The Relation of Leaf Area
to the Growth and Composition of Apples. Amer. Soc.
Hort. Sci., pp. 189-196 (1925).

MacDougal, D. T., mdration and Growth, Carnegie Inst.
Washington, Pub. 297, pp. 166-172 (1920).

MacDougal, D. T., The Physical Factors in the Growth of the
Tomato, Torrey Bot. Club, Bull. 47, pp. 261-271 (1920).

Murneek, Andrew E. Effects of correlat ion between Vegetative
and Reproductive Junctions in the Tomato, Plant Physiol-
ogy Vol. I, pp. 3-56 (1925).

01ney, L. 1., Some Experiments with Tomatoes. Ky. Lgr. Exp.
Sta. Bull. 218 (1918).

Ross, J’. T. Jr., Better Methods of Tomato Production, Mo.
Agr. Exp. St.e Bulle 19‘ (1928)e

StUCkny, He Pe Tomatoelg Gae Agr..EIp. Stle Bulle 118 (1915)e
Tincker, M. A. H., The Effect of length of Daily Period of

Illunination upon the Growth of Plants. Jour. Roy. Hort.
Soc., pp. 354-379 (1929).

15. Whipple, 0. B. and 1.. G. Schemerhorn, Tomato Tests,
Mbnt. Agr. Exp. Sta. Bull. 104 (1915).

16. Winkler, A. .T. The Relation of Number of leaves to Size
and Quality of Table Grapes, U. of Calif., Davis,
Calif. Proc. Amer. Soc. Hort. Sci., pp. 158-161,
(1930).

Plate

Plate

Plate

Plate

Plate

Plate

Plate

Plate

Plate

I.

II.

III.

IV.

V.

VII.

VIII.

APPENDIX
Explanation of Plates

Comparative average size of tomatoes that were grown
on the fall crop of plants. The letters at the side
indicate the lot of plants each tomato represents.

Comparative average size of tomatoes that were grown
on the spring crop of plants. The letters at the side
indicate the lot of plants each tomato represents.

A plant of fall crOp on left and A plant of spring crop
on right. Note severe curling of foliage on the spring
crop but there is more leaf area on the spring plant
than on the fall plant.

B plant of fall crOp on left and B plant of spring crOp
on the right. The fall crop had thicker stems but
smaller leaves and fruit.

0 plant of fall crop on left and 0 plant of spring crop
on the right. The large tomato second from the top on
the left is the largest produced on the fall crop of

0 plants.

D plant of fall crop on left and D plant of spring crop
on the right. Note the big difference of heighth of
these two plants. This holds true on all lots of
plants.

E plant of fall crop on left and E plant of’spring crop
on right. The tomatoes on the fall plant were the
largest produced on the fall crop. ‘Note how the plants
differ in leaf curling.

1" plant of fall crop on left and F plant of spring crop
on right. The results of a large amount of foliage in
fall and spring is well illustrated in this plate.

G plant of fall crop on left and G plant of spring crop
on right. This shows how small the tomatoes appear
when there is an excess of foliage per fruit. EVident-
ly the effect is greater in the spring than in the
fall.

Plate Xe

H plant of fall crop on left and.H plant of spring
crop on right. This will give one an idea of the
sturdy natural growth of the plants with a high
light intensity and the spindly natural growth of
the plants that have a low light intensity. It
will be noted that there was very little curling
on the plants that were allowed to grow naturally.

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