Directory UMM :Data Elmu:jurnal:S:Scientia Horticulturae:Vol86.Issue3.Nov2000:
Scientia Horticulturae 86 (2000) 197±210
Effect of frequency of axillary bud pruning
on vegetative growth and fruit yield in
greenhouse tomato crops
M. Navarretea,*, B. Jeannequinb
a
Institut National de la Recherche Agronomique, Station d'EcodeÂveloppement,
Site Agroparc, 84-914 Avignon Cedex 9, France
b
Institut National de la Recherche Agronomique, Domaine horticole du Mas Blanc,
66-200 AleÂnya, France
Accepted 12 February 2000
Abstract
In greenhouse tomato crops, several manual operations are performed each week to keep the
plants in optimal growth conditions. But growers are trying to reduce labour costs by spacing out
the manual operations. An experimental study was conducted on one particular operation, axillary
bud deshooting. The aim is to determine the effect of the deshooting frequency on vegetative growth
and fruit yield, in order to help growers to determine the optimal frequency. The trials were
conducted in an experimental station in AleÂnya (south France). Four deshooting frequencies were
compared on two cultivars: every 7 (control), 10, 14 and 21 days. Deshooting frequency affected
both vegetative growth and yield: when deshooting was performed seldom (every 21 days), the stem
diameter and the vigour scored by experts were decreased; the number of fruits per m2 was also
reduced, leading to a signi®cantly lower yield. Moreover, the harvest started later than on the
control. When the axillary buds were eliminated frequently (7 days), even those located near the
apex, it reduced vegetative growth, but not yield. Therefore, from a biological point of view, the
optimal deshooting frequency lies between 7 and 14 days, probably depending on climate, season
and cultivar vigour. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Tomato; Fruit yield; Vegetative growth; Deshooting; Lycopersicon esculentum Mill.
*
Corresponding author. Tel.: 33-4-32-72-25-86; fax: 33-4-32-72-25-62.
E-mail address: navarret@avignon.inra.fr (M. Navarrete).
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 0 0 ) 0 0 1 4 7 - 3
198
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
1. Introduction
Greenhouse tomato production is very intensive and requires a high amount of
input, particularly energy and manpower. For example, labour costs amount to
about 30% of production costs. Several manual operations are performed very
steadily: removing the axillary shoots and training the main stem keeps the crop
in optimal conditions as regards light interception; delea®ng consists in removing
the oldest leaves, which are no longer photosynthetically active, in order to avoid
plant diseases and facilitate harvesting; truss pruning aims at adapting the fruit
load to assimilate production, in order to improve fruit grade and quality. For a
long time, growers and technical advisors thought that manual operations had to
be carried out about once a week to maximise the yield of tomato crops. But
drastic changes have occurred in the last 10 years. As competition among
production areas throughout Europe and the Mediterranean area is increasing and
tomato prices are decreasing, growers are trying to reduce production costs, in
particular labour costs. Some operations have been suppressed or replaced by
alternative less time-consuming methods (e.g. pollination, previously carried out
manually, is now done by bumblebees). For most of the other operations, growers
are trying to reduce the frequency at which they are carried out. For example,
delea®ng and training are sometimes performed only twice a month. At the same
time, several experiments have indicated that manual operations on tomato plants
stress them because they bring about frequent movements of the leaves and stems.
Buitelaar (1988) even found a reduction in the yield of 9% when tomato plants
were shaken every day and 17% when they were shaken twice a day. On sweet
pepper plants, a decrease in height, leaf area and yield was also observed when
plants were submitted to frequent mechanical measurements on leaves and fruits
(length, diameter) in comparison with plants which were never measured
(KlaÈring, 1999). This phenomenon, known by scientists as mechanically induced
stress (Biddington, 1986), also incites to reduce the frequency of manual
operations.
Nevertheless, the precise agronomic consequences of the various manual
operations are not yet known. They depend on several phenomena: when
reducing the frequency, plants are stressed less often, but each operation may be
more stressful (e.g. more leaves or axillary shoots are removed each time).
Moreover, plants should be in worse conditions between two successive
operations, as regards light interception, air circulation or disease risks.
This study deals with one particular operation: deshooting. This operation
consists in removing regularly lateral (or axillary) shoots, since it has been
established that the one-stem system is the simplest to conduct. The aim of this
study is to quantify the effect on vegetative growth and yield of reducing the
frequency of deshooting, in order to help to determine which is the optimal
frequency on an agronomical point of view.
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
199
No studies were found in the literature on the effect of deshooting frequency,
but one can say that it determines the age of the axillary shoots remaining on the
plant and therefore the carbon demand of these organs. A young axillary shoot, as
any young organ, is a sink and uses the assimilates produced by the leaves of the
main stem; when reducing the frequency, each axillary shoot grows longer and
becomes a stronger competitor for assimilates for the main stem, the roots and
fruits. Finally, the axillary shoot becomes a carbon source. But the relation
between the carbon status of the axillary shoot and the deshooting frequency is
not known. In a greenhouse trial, Hartmann (1977) compared 12 cultivars varying
in vigour. Plant vigour is a qualitative characterisation of vegetative growth, in
close correlation with leaf area, leaf dry weight and stem diameter (Hall, 1983;
Navarrete et al., 1997). The various cultivars produced varying amounts of
axillary shoots over the same period. Hartmann (1977) found a negative
correlation between the weight of axillary shoots collected and yield, which
con®rms that the axillary shoots are in competition with fruits. According to this
trial, reducing the frequency of deshooting may affect the yield.
In order to determine the effects on plants of reducing the frequency of
deshooting, two experiments were conducted in 1996 and 1998, which made it
possible to test four deshooting frequencies.
2. Materials and methods
2.1. The plants and cropping conditions
Both experiments were conducted in a high greenhouse located at the INRA
station of AleÂnya (south France). The double-rows were aligned SE±NW. There
was no carbon dioxide enrichment. The mean temperatures were 168C at night
and 198C at day in winter, and 188C at night and 238C at day in spring and
summer. The temperature was adapted weekly to the external climate and to the
vigour of the plants. The climatic conditions are summarised in Table 1. Plant
nutrition followed commercial practices.
Experiment 1 (1996). Seeds of Lycopersicon esculentum Mill. (cv. Synergie)
were sown in a nursery on 15 November 1995, and transferred onto a rockwool
substrate in the greenhouse on 21 December. They were planted on 12 January
1996 at 2.4 plants/m2. The trusses were pruned to ®ve fruits. The plants were
grown in the greenhouse until 23 August 1996, but the harvest stopped on 15 July
because at that time most of the fruits were affected by blossom-end-rot.
Experiment 2 (1998). Seeds (cv. Egeris) were sown on 22 October 1997,
transferred into the greenhouse on 26 November and planted on 16 December at
2.2 plants/m2. As in Experiment 1, the trusses were pruned to ®ve fruits. The crop
was stopped on 7 September 1998.
200
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Table 1
Climatic conditions of the two trials
December January
February March April
May
June
July August
Global radiationa (MJ/m2)
Experiment 1
140
Experiment 2
159
149
259
269
416
356
450
471
628
655
622
695
699
669
Mean temperatureb (8C)
Experiment 1
18.0
Experiment 2
17.3
18.2
18.2
17.4
19.2
17.9
19.2
19.0
21.1
19.4
22.9
20.9
24.9
23.8 23.0
a
b
589
504
The global radiation was measured outside the greenhouse.
The temperature was measured inside the greenhouse.
The major difference between the two cultivars was that Egeris is more
vigorous than Synergie.
2.2. The treatments and experimental design
As space is limited in experimental greenhouses, only a small number of
treatments could be compared in the same place. In this case, three out of four
deshooting frequencies were compared each year.
In Experiment 1, deshooting was carried out every 7, 10 or 14 days (the
treatments were called 7D, 10D and 14D, respectively). The 7D treatment was
considered as a control, since it is the frequency observed most often in
commercial holdings in France. In Experiment 2, the 7D and 14D treatments
were repeated. The third treatment (21D) consisted in deshooting every 14 days
till 31 March, and from then on every 21 days; this treatment was supposed to
better suit the variations of vegetative growth during the cropping cycle: as plants
are getting older, their growth rate is reduced (de Koning, 1994), and we
hypothesised that deshooting could be done less often in the last part of the cycle.
Moreover, the 21D treatment was also justi®ed by labour organisation trends in
greenhouse holdings: when harvest begins, the other manual operations are
performed less frequently through lack of time.
All the treatments consisted in removing all the axillary shoots of the plant by
hand, as is done in greenhouse holdings. For the 7D treatment of the ®rst experiment, even the smaller axillary shoots located near the apex were removed. As this
appeared to be too stressful for the plants, only the axillary shoots over 2 cm were
removed in Experiment 2. The 14D treatments were identical in both experiments.
The greenhouse was divided into six blocks in Experiment 1 and four blocks in
Experiment 2, to take into account the climatic heterogeneity of the greenhouse.
In each block, the three treatments were applied randomly. The plots in
Experiments 1 and 2 contained nine and eight plants, respectively, in one row.
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
201
2.3. Scores and measurements
The main aim of the trials was to determine the effects of deshooting on yield.
But several other variables were measured to characterise the deshooting
treatments and analyse their consequences on vegetative growth.
Each time the axillary shoots were removed from the plants, they were dried in
an oven at 908C for 2 days and weighed. The total weight per plot was recorded.
This made it possible to quantify and compare the treatments.
The vegetative growth of the main shoot was estimated visually by vigour
scores and by stem diameter measurements. Both notations are useful: the
vigour score is an accurate estimation of the vegetative growth of plants and is
more comprehensive than stem diameter; but stem diameter is an objective
indicator of the vegetative dry weight and leaf area of a plant (Hall, 1983;
Navarrete et al., 1997). The vigour was scored plant by plant by two experts on a
scoring scale ranging from 1 to 3, according to the protocol de®ned by Navarrete
et al. (1997). The stem diameter was measured using a calliper. As it evolved
along the plant, it was measured at several levels along the stem, between trusses
2 and 14 in Experiment 1 and trusses 10 and 28 in Experiment 2, every two
trusses. At one particular level, the measurement was made 1 cm above the truss,
when the stem had reached its maximum width, i.e. when the third truss above
had ¯owered.
The fruits were harvested once to twice a week, depending on the season and
internal climate of the greenhouse. We recorded the number and weight of mature
fruits on each plot, separating the marketable and unmarketable fruits. The
harvest stopped on 15 July in Experiment 1, and 7 September in Experiment 2. In
Experiment 1, the number of set fruits was also recorded on each truss, in order to
detect possible defaults of fruit setting.
The ¯owering stage was estimated every 2 weeks by the number of the last
truss in bloom and the number of open ¯owers on it, and the duration of
development was expressed in degree-days from the sum of mean daily
temperature (with a base temperature equal to 08C).
3. Results
3.1. Characterisation of the experimental treatments
The cumulated dry weight of the removed axillary shoots is shown in Fig. 1.
In Experiment 1, from the ®rst measurements, the 14D treatment clearly
differed from 7D treatment; the 10D treatment began to differ from the 7D
only 150 days after sowing, that is about mid-April. From a technical point
of view, this indicates that before mid-April it was not necessary to remove
202
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Fig. 1. The dynamics of cumulative dry weight production of axillary shoots in Experiment 1 (a)
and Experiment 2 (b) when axillary shoots were removed every 7 (), 10 (&), 14 (&) or 21 days
(*). The vertical bars represent the con®dence intervals at P0.05 at two dates.
the axillary shoots on a weekly basis, every 10 days being suf®cient. After
mid-April, light and temperature in the greenhouse increased, and deshooting
only every 10 days led to increasing losses of dry matter. The curves were similar
in Experiment 2: the 14D treatment clearly differed from that of 7D from the ®rst
measurements; the dry weight of shoots produced in the 21D treatment was
greater than in the 14D treatment as soon as the deshooting frequency increased
from 14 to 21 days, i.e. from 31 March (160 days after sowing). At the end of the
experiments, the dry weight of axillary shoots produced in the 14D treatment was
3.8 and 2.5 times as much as in the 7D treatment, in Experiments 1 and 2,
respectively.
203
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Table 2
Effects of deshooting frequency on vegetative growtha
Treatments Vigour scores
Mean stem diameter (mm)
Experiment 1 Experiment 2 Experiment 2
(truss 21)
(truss 14)
(truss 27)
Experiment 1 Experiment 2 Experiment 2
(trusses 2±14) (trusses 10±16) (trusses 22±28)
7D
10D
14D
21D
2.8
2.7
2.8
±
3.4a
±
3.0b
2.8b
2.7
±
2.7
2.4
13.15a
13.50b
13.45b
±
14.10
±
13.87
13.55
14.50a
±
13.99b
13.47c
P
0.7740
ns
0.0083
0.6925
ns
0.0227
0.1085
ns
0.0005
**
*
***
a
For each experiment, the level at which measurements were made is indicated in brackets. The trusses
indicated for vigour scores are those in ¯ower when vigour was recorded. Figures followed by the same letter are
not signi®cantly different at 5% level.
nsnon-signi®cant.
*
Signi®cant at 5% level.
**
Signi®cant at 7% level.
***
Signi®cant at 10% level.
3.2. Effect of the treatments on development and vegetative growth
The number of trusses appeared per day varied from 0.10 in winter to 0.16 in
summer (Experiment 1), depending on the temperature in the greenhouse. In
south France, the temperature under the greenhouse in winter mainly depends on
the heating system, whereas in summer, it increases because of the outside
temperature (Table 1). On the whole season, the mean values were 0.121 and
0.123 trusses per day in Experiments 1 and 2, respectively, i.e. 5.9910ÿ3 and
6.0410ÿ3 truss per degree-day. Therefore, there was no signi®cant difference on
development rate between the two cultivars. The deshooting frequency had no
signi®cant effect on development rate (not shown).
Vegetative growth was estimated by two kinds of measurements: vigour scores
and stem diameter measurements (Table 2). The diameter and vigour evolved
along the stem, on a similar way for all the treatments (Fig. 2). In Experiment 1
(Fig. 2a), the higher values were observed on the lower part of the plant (i.e.
during the ®rst part of the cropping cycle, when fruit load was small). Then, stem
diameter decreased until harvest began, i.e. at the level of truss 8. Stem diameter
tended to increase later on (Fig. 2b), depending on the reproductive/vegetative
balance on the plant.
Only the mean values per plant are indicated in Table 2. In Experiment 1, the
7D treatment had a lower stem diameter (measured between trusses 2 and 14)
than the other two treatments, which were not signi®cantly different. There was
no difference in vigour scores, probably because it was recorded much later than
204
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Fig. 2. The effect of deshooting treatments on stem diameter in Experiment 1 (a) and Experiment 2
(b) when axillary shoots were removed every 7 (Ð Ð), 14 (Ð & Ð) or 21 days (± * ±). The
10D treatment is not shown as it never signi®cantly differed from the 14D treatment. Trusses are
numbered in their order of appearance.
stem diameter, at the level of truss 21. On the contrary, in Experiment 2, the 7D
treatment had a larger stem diameter than that of 14D, which was in turn higher
than that of 21D. The differences were very signi®cant on the higher part of the
plants (at the level of trusses 22±28) and nearly signi®cant in the middle part of
the plants (trusses 10±16). As regards vigour scores, the 7D treatment was more
vigorous than the other two at the ¯owering of truss 14, and the differences were
signi®cant. The vigour of the 14D and 21D treatments was similar, which is
consistent with the fact that, when plant vigour was noted (on 5 April), the plants
of the 21D treatment were still deshooted every 14 days, as in the 14D treatment.
On 20 July, at the ¯owering of truss 27, the vigours of the three treatments were
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
205
no longer signi®cantly different, although plants had been subjected to the
different treatments for a long time. This was probably due to increased
heterogeneity among plants of a same plot (diseases, broken plants), which was
all the higher as the size of the samples was rather small.
The results observed on vigour and stem diameter are consistent: the treatments
which had the most vigorous plants (higher values of vigour) also had the plants
with the largest stem diameter, when it was measured at the level of trusses which
had ¯owered at the time of vigour scoring. This result had also been observed in
previous trials (Navarrete et al., 1997). But the stem diameter data from the two
experiments seem contradictory at ®rst sight. In fact, it is likely that the small
diameters measured on the 7D treatment of Experiment 1 is due to the deshooting
practice: the ®rst year of experimentation, the axillary shoots were removed
whatever their size, even if they were very young and near the apex, which may
have stressed the plant and decreased stem diameter of the 7D treatment. Except
for this treatment, it seems that vegetative growth decreases when the period
between two successive deshooting increases a lot (i.e. over more than 14 days).
The stem diameters measured at the same level on the plant (i.e. at the level of
trusses 10±14 for Experiment 1, and 10±16 for Experiment 2) on the 14D
treatment were 13.0 and 13.9 mm, respectively, which con®rms that Experiment 2
cultivar (Egeris) was more vigorous than Experiment 1 cultivar (Synergie).
3.3. Effect of the treatments on yield
In Experiment 1, harvesting began 130 days after sowing (2305 degree-days),
i.e. a bit later than in Experiment 2 (120 days, 2146 degree-days). As no
difference was observed on the duration of the vegetative phase, it means that the
period of fruit development was longer on Synergie cultivar than on Egeris. After
a few weeks of harvesting, the total yield (marketable and unmarketable yield) in
Experiment 1 was higher than in Experiment 2 and this phenomenon was
observed throughout the cropping cycle, though the Experiment 1 cultivar was
weaker (Fig. 3). The most probable explanation is that the crop of Experiment 2
was sowed 3 weeks earlier and therefore, grew in worse light conditions (the
cumulated radiation on the ®rst 8 months was 3078 MJ/m2 in Experiment 1 and
2730 MJ/m2 in Experiment 2, i.e. 11% less). Unmarketable yield in Experiment 1
amounted to about 13% of the total yield and was due to blossom-end-rot. In
Experiment 2, it amounted only to 4%.
The total yield of the 21D treatment in Experiment 2 was about 7% lower than
that of the 7D treatment (Table 3). The difference was not signi®cant, but the
probability was rather low (P0.12). Therefore, deshooting rarely tended to
reduce yield. This result was identical on the marketable part, since unmarketable
yield was independent of the deshooting frequency. This slight reduction in yield
was due to a signi®cant decrease in the number of harvested fruits (Table 3),
206
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Fig. 3. The comparison of yield in the two experiments. The total (&) and marketable (&) yields
are compared 8 months (exactly 242 days) after sowing, i.e. at the end of the crop for Experiment 1
and on 21 July for Experiment 2. The vertical bars represent the con®dence intervals at P0.05.
whereas mean fruit weight was not affected. As we have no information in
Experiment 2 on the number of fruits per truss, it is impossible to determine
whether deshooting frequency affected fruit setting or the duration of the growing
period. The yields in the 7D and 14D treatments were nearly equal as regards
Table 3
Effects of deshooting frequency on yield componentsa
Treatments
Yield components on 3 August (Experiment 2)
Earliness of harvesting
Total yield
(kg/m2)
Experiment 1
Marketable yield
No. fruits
per m2
Mean fruit
weight (g)
No. fruits per m2 on
9 April
5 March
15.2a
12.9b
13.1b
±
9.5
±
8.1
7.4
0.0436
0.1041
ns
7D
10D
14D
21D
32.2
222a
141
31.6
30.1
224a
211b
138
140
P
0.1193
ns
0.0142
*
0.6007
ns
a
Experiment 2
*
The earliness of harvesting is estimated by the amount of fruits collected within the ®rst 15
days of harvest. Figures followed by the same letter are not signi®cantly different at 5% level.
nsnon-signi®cant.
*
Signi®cant at 5% level.
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
207
total or marketable yield. In Experiment 1, the yield of the 14D treatment was
slightly lower than that of the 7D one, but the difference was not signi®cant.
These results show the effects of deshooting frequency on the ®nal yield. But
growers are also interested in the time course of production, particularly in the
®rst months of production, because the prices are higher in winter than in spring.
Therefore, the number of fruits harvested during the 15 ®rst days was also
analysed. In both experiments, the 7D treatments produced a greater number of
fruits 15 days after the beginning of harvesting (Table 3) and was therefore earlyfruiting. The difference was signi®cant in Experiment 1 and nearly signi®cant in
Experiment 2.
4. Discussion
Four deshooting frequencies were compared in a 2-year trial, and their effects
on development, vegetative growth and yield were compared.
The axillary shoots left on the plants until the next deshooting operation
consisted of a few young leaves (each one being shorter than 15 cm) and were
removed before the ®rst truss ¯owered on them. Their dry weight was all the
higher as the deshooting was performed less often (from 0.03 g per plant per day
for the 7D treatment to 0.19 for the 21D one). This result is consistent with the
dynamics of dry weight accumulation in shoots, which is exponential: the longer
the shoots are left on the plants, the higher their growth rate. In Experiment 2, on
3 August, the weight of the axillary shoots was compared to the total dry weight
of the plants, which was estimated. Assuming that 23 of the assimilates are diverted
to fruits and that fruit water content is 94% (Ho and Hewitt, 1986), and
considering the total yield of each treatment on 3 August, the axillary shoots
represented at that date 0.6, 1.7 and 3.3% of the estimated plant's dry weight
production for the 7D, 14D and 21D treatments, respectively. The data from
Experiment 1 lead to the same conclusion. These fractions are rather low and
nevertheless, the frequency at which axillary shoots are removed appear to have
several consequences on vegetative growth and yield.
When deshooting was performed only every 21 days, the vigour and diameter
of the main stem was signi®cantly lowered in comparison with a deshooting
every 7 days, which indicates a decrease in vegetative growth and leaf area
(Navarrete et al., 1997). This phenomenon led to a small decrease in yield and in
particular in the number of fruits harvested. These results are consistent with
those of Hartmann (1977) although they have been observed in different
conditions: Hartmann (1977) tested the vigour effect and not the deshooting
operation effect; he demonstrated that yield was decreased when the weight of
axillary shoots remaining on the plant was heavy: one explanation is that, until
the axillary shoots are removed, a part of the assimilates produced by the main
208
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
stem is diverted to them, at the expense of vegetative and fruit growth on the main
stem. The same phenomenon may explain the present results on the 21D
treatment although no study was found in the literature on dry matter partitioning
between the main stem and the axillary shoots. Yet, experimental measurements
of dry matter partitioning on tomato plants have been always made on plants
whose axillary shoots have been removed, as in commercial crops (e.g. Khan and
Sagar, 1967; Heuvelink and Marcelis, 1989). When axillary shoots are left on
plants to increase crop density (to ®t better the increase in radiation in spring), dry
matter production and partitioning are observed only when plants already bear
fruits (Cockshull and Ho, 1995; Delambre, 1998), and not in the transitional
phase.
In our experiment, the harvest started later on plants of the 21D treatment than
on those of the 7D treatment. Kazanovich (cited by Aung and Kelly, 1966)
compared deshooted plants and plants which were never deshooted; he also found
a positive effect of deshooting on early ripening of tomato fruits. In the present
trials, when plants were deshooted every 14 days, the effects were qualitatively
similar to the case of deshooting every 21 days, but rather limited.
In the 7D treatment of Experiment 1, the plants were deshooted weekly and
even the smaller shoots located near the apex were removed. Therefore, the
weight of axillary shoot collected each time was low. In that case, the stem
diameter was smaller than that in the 14D treatment, but yield was not affected.
This phenomenon could be due to the mechanical stress caused by the high
frequency of deshooting operations performed during the season. Tomato is
known to be a species which is rather sensitive to mechanical stress (Heuchert
and Mitchell, 1983). Biddington (1986) and Mitchell and Myers (1995) reviewed
several studies on mechanical stress, on several species. On tomato, most of the
mechanical stresses tested reduce leaf area and leaf dry weight, stem diameter
and even sometimes yield. But usually, the experimental treatments tested differ
greatly to the reality of greenhouse production, and the effects of involuntary
plant movements have not been tested. The studies which most closely resemble
greenhouse tomato crop conditions are those of Buitelaar (1988): the
experimental treatments consisted in taking the head of each plant between the
thumb and fore®nger, and lifting the plant vigorously up and down three or four
times. This movement reduced the mean weight of the fruits and provoked a
magnesium de®ciency, which also had a negative effect on fruit yield. The effects
were all the greater as the plants were moved frequently. This could explain why,
in Experiment 1, the stem diameter of the 7D treatment was the lowest of all the
treatments experimented.
Anyway, as not enough is known about the phenomena involved in deshooting,
we cannot determine which, out of dry matter partitioning and mechanical stress,
is the main phenomenon and how their effects were combined for each frequency
of deshooting. But these trials make it possible to determine the upper limit that
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
209
should not be passed to prevent a yield decrease, which is about 2 weeks.
Deshooting every 3 weeks must be avoided, since vegetative growth and yield are
affected. Within 1±2 weeks, no signi®cant trend on yield or vegetative growth
was observed, and the choice of the deshooting frequency will depend on labour
organisation in the horticultural holding. In particular, a deshooting operation
performed after 14 days takes more time than that after 7 days because a larger
number of shoots must be removed, but the labour cost calculated over the whole
cropping cycle is reduced. Yet, in some holdings, growers prefer to go on
deshooting weekly for practical reasons, because this operation is performed at
the same time as truss pruning, which is necessarily done weekly. Moreover, it
appears that deshooting every week enables earlier harvest, which is rather
interesting from an economical point of view.
Acknowledgements
The authors are grateful to L. Pares (INRA AleÂnya) for technical assistance.
References
Aung, L.H., Kelly, W.C., 1966. In¯uence of defoliation on vegetative, ¯oral and fruit development
in tomatoes (Lycopersicon esculentum Mill.). Am. Soc. Hort. Sci. 89, 563±570.
Biddington, N., 1986. The effect of mechanically induced stress in plants Ð a review. Plant growth
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Buitelaar, K., 1988. Are your tomatoes a little shaky? Grower, February 4, 1988, pp. 32±33.
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quantitative approach. Thesis. Agricultural University, Wageningen, the Netherland, 240 pp.
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l'effet de la charge en fruits et de la densite de peuplement. ConseÂquences pour le modeÁle
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Hall, D., 1983. The in¯uence of nitrogen concentration and salinity of recirculating solutions on the
early season vigour and productivity of glasshouse tomatoes. J. Hort. Sci. 58, 411±415.
Hartmann, H.D., 1977. In¯uence of axillary shoots on growth and yield of tomato varieties.
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Effect of frequency of axillary bud pruning
on vegetative growth and fruit yield in
greenhouse tomato crops
M. Navarretea,*, B. Jeannequinb
a
Institut National de la Recherche Agronomique, Station d'EcodeÂveloppement,
Site Agroparc, 84-914 Avignon Cedex 9, France
b
Institut National de la Recherche Agronomique, Domaine horticole du Mas Blanc,
66-200 AleÂnya, France
Accepted 12 February 2000
Abstract
In greenhouse tomato crops, several manual operations are performed each week to keep the
plants in optimal growth conditions. But growers are trying to reduce labour costs by spacing out
the manual operations. An experimental study was conducted on one particular operation, axillary
bud deshooting. The aim is to determine the effect of the deshooting frequency on vegetative growth
and fruit yield, in order to help growers to determine the optimal frequency. The trials were
conducted in an experimental station in AleÂnya (south France). Four deshooting frequencies were
compared on two cultivars: every 7 (control), 10, 14 and 21 days. Deshooting frequency affected
both vegetative growth and yield: when deshooting was performed seldom (every 21 days), the stem
diameter and the vigour scored by experts were decreased; the number of fruits per m2 was also
reduced, leading to a signi®cantly lower yield. Moreover, the harvest started later than on the
control. When the axillary buds were eliminated frequently (7 days), even those located near the
apex, it reduced vegetative growth, but not yield. Therefore, from a biological point of view, the
optimal deshooting frequency lies between 7 and 14 days, probably depending on climate, season
and cultivar vigour. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Tomato; Fruit yield; Vegetative growth; Deshooting; Lycopersicon esculentum Mill.
*
Corresponding author. Tel.: 33-4-32-72-25-86; fax: 33-4-32-72-25-62.
E-mail address: navarret@avignon.inra.fr (M. Navarrete).
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 0 0 ) 0 0 1 4 7 - 3
198
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
1. Introduction
Greenhouse tomato production is very intensive and requires a high amount of
input, particularly energy and manpower. For example, labour costs amount to
about 30% of production costs. Several manual operations are performed very
steadily: removing the axillary shoots and training the main stem keeps the crop
in optimal conditions as regards light interception; delea®ng consists in removing
the oldest leaves, which are no longer photosynthetically active, in order to avoid
plant diseases and facilitate harvesting; truss pruning aims at adapting the fruit
load to assimilate production, in order to improve fruit grade and quality. For a
long time, growers and technical advisors thought that manual operations had to
be carried out about once a week to maximise the yield of tomato crops. But
drastic changes have occurred in the last 10 years. As competition among
production areas throughout Europe and the Mediterranean area is increasing and
tomato prices are decreasing, growers are trying to reduce production costs, in
particular labour costs. Some operations have been suppressed or replaced by
alternative less time-consuming methods (e.g. pollination, previously carried out
manually, is now done by bumblebees). For most of the other operations, growers
are trying to reduce the frequency at which they are carried out. For example,
delea®ng and training are sometimes performed only twice a month. At the same
time, several experiments have indicated that manual operations on tomato plants
stress them because they bring about frequent movements of the leaves and stems.
Buitelaar (1988) even found a reduction in the yield of 9% when tomato plants
were shaken every day and 17% when they were shaken twice a day. On sweet
pepper plants, a decrease in height, leaf area and yield was also observed when
plants were submitted to frequent mechanical measurements on leaves and fruits
(length, diameter) in comparison with plants which were never measured
(KlaÈring, 1999). This phenomenon, known by scientists as mechanically induced
stress (Biddington, 1986), also incites to reduce the frequency of manual
operations.
Nevertheless, the precise agronomic consequences of the various manual
operations are not yet known. They depend on several phenomena: when
reducing the frequency, plants are stressed less often, but each operation may be
more stressful (e.g. more leaves or axillary shoots are removed each time).
Moreover, plants should be in worse conditions between two successive
operations, as regards light interception, air circulation or disease risks.
This study deals with one particular operation: deshooting. This operation
consists in removing regularly lateral (or axillary) shoots, since it has been
established that the one-stem system is the simplest to conduct. The aim of this
study is to quantify the effect on vegetative growth and yield of reducing the
frequency of deshooting, in order to help to determine which is the optimal
frequency on an agronomical point of view.
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
199
No studies were found in the literature on the effect of deshooting frequency,
but one can say that it determines the age of the axillary shoots remaining on the
plant and therefore the carbon demand of these organs. A young axillary shoot, as
any young organ, is a sink and uses the assimilates produced by the leaves of the
main stem; when reducing the frequency, each axillary shoot grows longer and
becomes a stronger competitor for assimilates for the main stem, the roots and
fruits. Finally, the axillary shoot becomes a carbon source. But the relation
between the carbon status of the axillary shoot and the deshooting frequency is
not known. In a greenhouse trial, Hartmann (1977) compared 12 cultivars varying
in vigour. Plant vigour is a qualitative characterisation of vegetative growth, in
close correlation with leaf area, leaf dry weight and stem diameter (Hall, 1983;
Navarrete et al., 1997). The various cultivars produced varying amounts of
axillary shoots over the same period. Hartmann (1977) found a negative
correlation between the weight of axillary shoots collected and yield, which
con®rms that the axillary shoots are in competition with fruits. According to this
trial, reducing the frequency of deshooting may affect the yield.
In order to determine the effects on plants of reducing the frequency of
deshooting, two experiments were conducted in 1996 and 1998, which made it
possible to test four deshooting frequencies.
2. Materials and methods
2.1. The plants and cropping conditions
Both experiments were conducted in a high greenhouse located at the INRA
station of AleÂnya (south France). The double-rows were aligned SE±NW. There
was no carbon dioxide enrichment. The mean temperatures were 168C at night
and 198C at day in winter, and 188C at night and 238C at day in spring and
summer. The temperature was adapted weekly to the external climate and to the
vigour of the plants. The climatic conditions are summarised in Table 1. Plant
nutrition followed commercial practices.
Experiment 1 (1996). Seeds of Lycopersicon esculentum Mill. (cv. Synergie)
were sown in a nursery on 15 November 1995, and transferred onto a rockwool
substrate in the greenhouse on 21 December. They were planted on 12 January
1996 at 2.4 plants/m2. The trusses were pruned to ®ve fruits. The plants were
grown in the greenhouse until 23 August 1996, but the harvest stopped on 15 July
because at that time most of the fruits were affected by blossom-end-rot.
Experiment 2 (1998). Seeds (cv. Egeris) were sown on 22 October 1997,
transferred into the greenhouse on 26 November and planted on 16 December at
2.2 plants/m2. As in Experiment 1, the trusses were pruned to ®ve fruits. The crop
was stopped on 7 September 1998.
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M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Table 1
Climatic conditions of the two trials
December January
February March April
May
June
July August
Global radiationa (MJ/m2)
Experiment 1
140
Experiment 2
159
149
259
269
416
356
450
471
628
655
622
695
699
669
Mean temperatureb (8C)
Experiment 1
18.0
Experiment 2
17.3
18.2
18.2
17.4
19.2
17.9
19.2
19.0
21.1
19.4
22.9
20.9
24.9
23.8 23.0
a
b
589
504
The global radiation was measured outside the greenhouse.
The temperature was measured inside the greenhouse.
The major difference between the two cultivars was that Egeris is more
vigorous than Synergie.
2.2. The treatments and experimental design
As space is limited in experimental greenhouses, only a small number of
treatments could be compared in the same place. In this case, three out of four
deshooting frequencies were compared each year.
In Experiment 1, deshooting was carried out every 7, 10 or 14 days (the
treatments were called 7D, 10D and 14D, respectively). The 7D treatment was
considered as a control, since it is the frequency observed most often in
commercial holdings in France. In Experiment 2, the 7D and 14D treatments
were repeated. The third treatment (21D) consisted in deshooting every 14 days
till 31 March, and from then on every 21 days; this treatment was supposed to
better suit the variations of vegetative growth during the cropping cycle: as plants
are getting older, their growth rate is reduced (de Koning, 1994), and we
hypothesised that deshooting could be done less often in the last part of the cycle.
Moreover, the 21D treatment was also justi®ed by labour organisation trends in
greenhouse holdings: when harvest begins, the other manual operations are
performed less frequently through lack of time.
All the treatments consisted in removing all the axillary shoots of the plant by
hand, as is done in greenhouse holdings. For the 7D treatment of the ®rst experiment, even the smaller axillary shoots located near the apex were removed. As this
appeared to be too stressful for the plants, only the axillary shoots over 2 cm were
removed in Experiment 2. The 14D treatments were identical in both experiments.
The greenhouse was divided into six blocks in Experiment 1 and four blocks in
Experiment 2, to take into account the climatic heterogeneity of the greenhouse.
In each block, the three treatments were applied randomly. The plots in
Experiments 1 and 2 contained nine and eight plants, respectively, in one row.
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
201
2.3. Scores and measurements
The main aim of the trials was to determine the effects of deshooting on yield.
But several other variables were measured to characterise the deshooting
treatments and analyse their consequences on vegetative growth.
Each time the axillary shoots were removed from the plants, they were dried in
an oven at 908C for 2 days and weighed. The total weight per plot was recorded.
This made it possible to quantify and compare the treatments.
The vegetative growth of the main shoot was estimated visually by vigour
scores and by stem diameter measurements. Both notations are useful: the
vigour score is an accurate estimation of the vegetative growth of plants and is
more comprehensive than stem diameter; but stem diameter is an objective
indicator of the vegetative dry weight and leaf area of a plant (Hall, 1983;
Navarrete et al., 1997). The vigour was scored plant by plant by two experts on a
scoring scale ranging from 1 to 3, according to the protocol de®ned by Navarrete
et al. (1997). The stem diameter was measured using a calliper. As it evolved
along the plant, it was measured at several levels along the stem, between trusses
2 and 14 in Experiment 1 and trusses 10 and 28 in Experiment 2, every two
trusses. At one particular level, the measurement was made 1 cm above the truss,
when the stem had reached its maximum width, i.e. when the third truss above
had ¯owered.
The fruits were harvested once to twice a week, depending on the season and
internal climate of the greenhouse. We recorded the number and weight of mature
fruits on each plot, separating the marketable and unmarketable fruits. The
harvest stopped on 15 July in Experiment 1, and 7 September in Experiment 2. In
Experiment 1, the number of set fruits was also recorded on each truss, in order to
detect possible defaults of fruit setting.
The ¯owering stage was estimated every 2 weeks by the number of the last
truss in bloom and the number of open ¯owers on it, and the duration of
development was expressed in degree-days from the sum of mean daily
temperature (with a base temperature equal to 08C).
3. Results
3.1. Characterisation of the experimental treatments
The cumulated dry weight of the removed axillary shoots is shown in Fig. 1.
In Experiment 1, from the ®rst measurements, the 14D treatment clearly
differed from 7D treatment; the 10D treatment began to differ from the 7D
only 150 days after sowing, that is about mid-April. From a technical point
of view, this indicates that before mid-April it was not necessary to remove
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M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Fig. 1. The dynamics of cumulative dry weight production of axillary shoots in Experiment 1 (a)
and Experiment 2 (b) when axillary shoots were removed every 7 (), 10 (&), 14 (&) or 21 days
(*). The vertical bars represent the con®dence intervals at P0.05 at two dates.
the axillary shoots on a weekly basis, every 10 days being suf®cient. After
mid-April, light and temperature in the greenhouse increased, and deshooting
only every 10 days led to increasing losses of dry matter. The curves were similar
in Experiment 2: the 14D treatment clearly differed from that of 7D from the ®rst
measurements; the dry weight of shoots produced in the 21D treatment was
greater than in the 14D treatment as soon as the deshooting frequency increased
from 14 to 21 days, i.e. from 31 March (160 days after sowing). At the end of the
experiments, the dry weight of axillary shoots produced in the 14D treatment was
3.8 and 2.5 times as much as in the 7D treatment, in Experiments 1 and 2,
respectively.
203
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Table 2
Effects of deshooting frequency on vegetative growtha
Treatments Vigour scores
Mean stem diameter (mm)
Experiment 1 Experiment 2 Experiment 2
(truss 21)
(truss 14)
(truss 27)
Experiment 1 Experiment 2 Experiment 2
(trusses 2±14) (trusses 10±16) (trusses 22±28)
7D
10D
14D
21D
2.8
2.7
2.8
±
3.4a
±
3.0b
2.8b
2.7
±
2.7
2.4
13.15a
13.50b
13.45b
±
14.10
±
13.87
13.55
14.50a
±
13.99b
13.47c
P
0.7740
ns
0.0083
0.6925
ns
0.0227
0.1085
ns
0.0005
**
*
***
a
For each experiment, the level at which measurements were made is indicated in brackets. The trusses
indicated for vigour scores are those in ¯ower when vigour was recorded. Figures followed by the same letter are
not signi®cantly different at 5% level.
nsnon-signi®cant.
*
Signi®cant at 5% level.
**
Signi®cant at 7% level.
***
Signi®cant at 10% level.
3.2. Effect of the treatments on development and vegetative growth
The number of trusses appeared per day varied from 0.10 in winter to 0.16 in
summer (Experiment 1), depending on the temperature in the greenhouse. In
south France, the temperature under the greenhouse in winter mainly depends on
the heating system, whereas in summer, it increases because of the outside
temperature (Table 1). On the whole season, the mean values were 0.121 and
0.123 trusses per day in Experiments 1 and 2, respectively, i.e. 5.9910ÿ3 and
6.0410ÿ3 truss per degree-day. Therefore, there was no signi®cant difference on
development rate between the two cultivars. The deshooting frequency had no
signi®cant effect on development rate (not shown).
Vegetative growth was estimated by two kinds of measurements: vigour scores
and stem diameter measurements (Table 2). The diameter and vigour evolved
along the stem, on a similar way for all the treatments (Fig. 2). In Experiment 1
(Fig. 2a), the higher values were observed on the lower part of the plant (i.e.
during the ®rst part of the cropping cycle, when fruit load was small). Then, stem
diameter decreased until harvest began, i.e. at the level of truss 8. Stem diameter
tended to increase later on (Fig. 2b), depending on the reproductive/vegetative
balance on the plant.
Only the mean values per plant are indicated in Table 2. In Experiment 1, the
7D treatment had a lower stem diameter (measured between trusses 2 and 14)
than the other two treatments, which were not signi®cantly different. There was
no difference in vigour scores, probably because it was recorded much later than
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M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Fig. 2. The effect of deshooting treatments on stem diameter in Experiment 1 (a) and Experiment 2
(b) when axillary shoots were removed every 7 (Ð Ð), 14 (Ð & Ð) or 21 days (± * ±). The
10D treatment is not shown as it never signi®cantly differed from the 14D treatment. Trusses are
numbered in their order of appearance.
stem diameter, at the level of truss 21. On the contrary, in Experiment 2, the 7D
treatment had a larger stem diameter than that of 14D, which was in turn higher
than that of 21D. The differences were very signi®cant on the higher part of the
plants (at the level of trusses 22±28) and nearly signi®cant in the middle part of
the plants (trusses 10±16). As regards vigour scores, the 7D treatment was more
vigorous than the other two at the ¯owering of truss 14, and the differences were
signi®cant. The vigour of the 14D and 21D treatments was similar, which is
consistent with the fact that, when plant vigour was noted (on 5 April), the plants
of the 21D treatment were still deshooted every 14 days, as in the 14D treatment.
On 20 July, at the ¯owering of truss 27, the vigours of the three treatments were
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
205
no longer signi®cantly different, although plants had been subjected to the
different treatments for a long time. This was probably due to increased
heterogeneity among plants of a same plot (diseases, broken plants), which was
all the higher as the size of the samples was rather small.
The results observed on vigour and stem diameter are consistent: the treatments
which had the most vigorous plants (higher values of vigour) also had the plants
with the largest stem diameter, when it was measured at the level of trusses which
had ¯owered at the time of vigour scoring. This result had also been observed in
previous trials (Navarrete et al., 1997). But the stem diameter data from the two
experiments seem contradictory at ®rst sight. In fact, it is likely that the small
diameters measured on the 7D treatment of Experiment 1 is due to the deshooting
practice: the ®rst year of experimentation, the axillary shoots were removed
whatever their size, even if they were very young and near the apex, which may
have stressed the plant and decreased stem diameter of the 7D treatment. Except
for this treatment, it seems that vegetative growth decreases when the period
between two successive deshooting increases a lot (i.e. over more than 14 days).
The stem diameters measured at the same level on the plant (i.e. at the level of
trusses 10±14 for Experiment 1, and 10±16 for Experiment 2) on the 14D
treatment were 13.0 and 13.9 mm, respectively, which con®rms that Experiment 2
cultivar (Egeris) was more vigorous than Experiment 1 cultivar (Synergie).
3.3. Effect of the treatments on yield
In Experiment 1, harvesting began 130 days after sowing (2305 degree-days),
i.e. a bit later than in Experiment 2 (120 days, 2146 degree-days). As no
difference was observed on the duration of the vegetative phase, it means that the
period of fruit development was longer on Synergie cultivar than on Egeris. After
a few weeks of harvesting, the total yield (marketable and unmarketable yield) in
Experiment 1 was higher than in Experiment 2 and this phenomenon was
observed throughout the cropping cycle, though the Experiment 1 cultivar was
weaker (Fig. 3). The most probable explanation is that the crop of Experiment 2
was sowed 3 weeks earlier and therefore, grew in worse light conditions (the
cumulated radiation on the ®rst 8 months was 3078 MJ/m2 in Experiment 1 and
2730 MJ/m2 in Experiment 2, i.e. 11% less). Unmarketable yield in Experiment 1
amounted to about 13% of the total yield and was due to blossom-end-rot. In
Experiment 2, it amounted only to 4%.
The total yield of the 21D treatment in Experiment 2 was about 7% lower than
that of the 7D treatment (Table 3). The difference was not signi®cant, but the
probability was rather low (P0.12). Therefore, deshooting rarely tended to
reduce yield. This result was identical on the marketable part, since unmarketable
yield was independent of the deshooting frequency. This slight reduction in yield
was due to a signi®cant decrease in the number of harvested fruits (Table 3),
206
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
Fig. 3. The comparison of yield in the two experiments. The total (&) and marketable (&) yields
are compared 8 months (exactly 242 days) after sowing, i.e. at the end of the crop for Experiment 1
and on 21 July for Experiment 2. The vertical bars represent the con®dence intervals at P0.05.
whereas mean fruit weight was not affected. As we have no information in
Experiment 2 on the number of fruits per truss, it is impossible to determine
whether deshooting frequency affected fruit setting or the duration of the growing
period. The yields in the 7D and 14D treatments were nearly equal as regards
Table 3
Effects of deshooting frequency on yield componentsa
Treatments
Yield components on 3 August (Experiment 2)
Earliness of harvesting
Total yield
(kg/m2)
Experiment 1
Marketable yield
No. fruits
per m2
Mean fruit
weight (g)
No. fruits per m2 on
9 April
5 March
15.2a
12.9b
13.1b
±
9.5
±
8.1
7.4
0.0436
0.1041
ns
7D
10D
14D
21D
32.2
222a
141
31.6
30.1
224a
211b
138
140
P
0.1193
ns
0.0142
*
0.6007
ns
a
Experiment 2
*
The earliness of harvesting is estimated by the amount of fruits collected within the ®rst 15
days of harvest. Figures followed by the same letter are not signi®cantly different at 5% level.
nsnon-signi®cant.
*
Signi®cant at 5% level.
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
207
total or marketable yield. In Experiment 1, the yield of the 14D treatment was
slightly lower than that of the 7D one, but the difference was not signi®cant.
These results show the effects of deshooting frequency on the ®nal yield. But
growers are also interested in the time course of production, particularly in the
®rst months of production, because the prices are higher in winter than in spring.
Therefore, the number of fruits harvested during the 15 ®rst days was also
analysed. In both experiments, the 7D treatments produced a greater number of
fruits 15 days after the beginning of harvesting (Table 3) and was therefore earlyfruiting. The difference was signi®cant in Experiment 1 and nearly signi®cant in
Experiment 2.
4. Discussion
Four deshooting frequencies were compared in a 2-year trial, and their effects
on development, vegetative growth and yield were compared.
The axillary shoots left on the plants until the next deshooting operation
consisted of a few young leaves (each one being shorter than 15 cm) and were
removed before the ®rst truss ¯owered on them. Their dry weight was all the
higher as the deshooting was performed less often (from 0.03 g per plant per day
for the 7D treatment to 0.19 for the 21D one). This result is consistent with the
dynamics of dry weight accumulation in shoots, which is exponential: the longer
the shoots are left on the plants, the higher their growth rate. In Experiment 2, on
3 August, the weight of the axillary shoots was compared to the total dry weight
of the plants, which was estimated. Assuming that 23 of the assimilates are diverted
to fruits and that fruit water content is 94% (Ho and Hewitt, 1986), and
considering the total yield of each treatment on 3 August, the axillary shoots
represented at that date 0.6, 1.7 and 3.3% of the estimated plant's dry weight
production for the 7D, 14D and 21D treatments, respectively. The data from
Experiment 1 lead to the same conclusion. These fractions are rather low and
nevertheless, the frequency at which axillary shoots are removed appear to have
several consequences on vegetative growth and yield.
When deshooting was performed only every 21 days, the vigour and diameter
of the main stem was signi®cantly lowered in comparison with a deshooting
every 7 days, which indicates a decrease in vegetative growth and leaf area
(Navarrete et al., 1997). This phenomenon led to a small decrease in yield and in
particular in the number of fruits harvested. These results are consistent with
those of Hartmann (1977) although they have been observed in different
conditions: Hartmann (1977) tested the vigour effect and not the deshooting
operation effect; he demonstrated that yield was decreased when the weight of
axillary shoots remaining on the plant was heavy: one explanation is that, until
the axillary shoots are removed, a part of the assimilates produced by the main
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M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
stem is diverted to them, at the expense of vegetative and fruit growth on the main
stem. The same phenomenon may explain the present results on the 21D
treatment although no study was found in the literature on dry matter partitioning
between the main stem and the axillary shoots. Yet, experimental measurements
of dry matter partitioning on tomato plants have been always made on plants
whose axillary shoots have been removed, as in commercial crops (e.g. Khan and
Sagar, 1967; Heuvelink and Marcelis, 1989). When axillary shoots are left on
plants to increase crop density (to ®t better the increase in radiation in spring), dry
matter production and partitioning are observed only when plants already bear
fruits (Cockshull and Ho, 1995; Delambre, 1998), and not in the transitional
phase.
In our experiment, the harvest started later on plants of the 21D treatment than
on those of the 7D treatment. Kazanovich (cited by Aung and Kelly, 1966)
compared deshooted plants and plants which were never deshooted; he also found
a positive effect of deshooting on early ripening of tomato fruits. In the present
trials, when plants were deshooted every 14 days, the effects were qualitatively
similar to the case of deshooting every 21 days, but rather limited.
In the 7D treatment of Experiment 1, the plants were deshooted weekly and
even the smaller shoots located near the apex were removed. Therefore, the
weight of axillary shoot collected each time was low. In that case, the stem
diameter was smaller than that in the 14D treatment, but yield was not affected.
This phenomenon could be due to the mechanical stress caused by the high
frequency of deshooting operations performed during the season. Tomato is
known to be a species which is rather sensitive to mechanical stress (Heuchert
and Mitchell, 1983). Biddington (1986) and Mitchell and Myers (1995) reviewed
several studies on mechanical stress, on several species. On tomato, most of the
mechanical stresses tested reduce leaf area and leaf dry weight, stem diameter
and even sometimes yield. But usually, the experimental treatments tested differ
greatly to the reality of greenhouse production, and the effects of involuntary
plant movements have not been tested. The studies which most closely resemble
greenhouse tomato crop conditions are those of Buitelaar (1988): the
experimental treatments consisted in taking the head of each plant between the
thumb and fore®nger, and lifting the plant vigorously up and down three or four
times. This movement reduced the mean weight of the fruits and provoked a
magnesium de®ciency, which also had a negative effect on fruit yield. The effects
were all the greater as the plants were moved frequently. This could explain why,
in Experiment 1, the stem diameter of the 7D treatment was the lowest of all the
treatments experimented.
Anyway, as not enough is known about the phenomena involved in deshooting,
we cannot determine which, out of dry matter partitioning and mechanical stress,
is the main phenomenon and how their effects were combined for each frequency
of deshooting. But these trials make it possible to determine the upper limit that
M. Navarrete, B. Jeannequin / Scientia Horticulturae 86 (2000) 197±210
209
should not be passed to prevent a yield decrease, which is about 2 weeks.
Deshooting every 3 weeks must be avoided, since vegetative growth and yield are
affected. Within 1±2 weeks, no signi®cant trend on yield or vegetative growth
was observed, and the choice of the deshooting frequency will depend on labour
organisation in the horticultural holding. In particular, a deshooting operation
performed after 14 days takes more time than that after 7 days because a larger
number of shoots must be removed, but the labour cost calculated over the whole
cropping cycle is reduced. Yet, in some holdings, growers prefer to go on
deshooting weekly for practical reasons, because this operation is performed at
the same time as truss pruning, which is necessarily done weekly. Moreover, it
appears that deshooting every week enables earlier harvest, which is rather
interesting from an economical point of view.
Acknowledgements
The authors are grateful to L. Pares (INRA AleÂnya) for technical assistance.
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