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*Corresponding author. 21
Agricultural and Marine Sciences, 8(1):21-26 (2003)
© 2003 Sultan Qaboos University
Influence of Pollination Technique on
Greenhouse Tomato Production
Y.Z. Al-Attal
1
, M.A. Kasrawi
2
and I.K. Nazer
2
*
1
Integrated Pest Management Project, GTZ, Amman, Jordan.
2
Department of Horticulture and Plant Protection, Faculty of Agriculture,
University of Jordan, Amman 11942, Jordan.
ABSTRACT: An experiment was carried out to study the effects of four pollination techniques; Bumblebees (Bombus
terrerstris L.), plant growth bioregulator (PGB) (Parachlorophenoxy acetic acid), hand vibration, and control (natural
pollination) on tomato (Lycopersicon esculentum Mill) production in greenhouses. Bumblebees showed no problem in
visiting flowers at a temperature range of 17-42°C during the day and 2-14°C at night. Bumblebee pollinated plants
produced a yield per plant which was significantly higher than plants treated with PGB, vibration and the control,
respectively. Fruit set of tomato flowers over 10 clusters was 99.1, 96.7, 76.7, and 65.7% for bumblebee treatment,
PGB application, vibration and the control, respectively. In the bumblebee pollinated flowers, the quality of fruits was
superior. The fruits were hard, with more seeds, and had a high specific gravity and better appearance. The average
fruit weight was 100.3, 80.5, 84.1, and 70.6 g for the bumblebee, PGB, vibration and the control, respectively. The
PGB treatment produced bigger sized but puffy fruits (108.4 ml). While fruit size in the vibration treatment was the
highest (126.8 ml), followed by the bumblebee and the control which were 99.3 and 98.5 ml, respectively. Fruit
specific gravity in the bumblebee treatment was significantly higher than other treatments, with no significant
differences between the PGB and the vibration treatments. The least dense fruits were in the control treatment.
Regarding the firmness of fruits, the bumblebee treatment gave the hardest fruits, while the PGB and the vibration
treatments were intermediate and the control was the least. Average seed number per fruit was 177.0, 86.5, 61.8, and
89.8 for bumblebee, vibration, PGB and the control, respectively.
Keywords: Bumblebees, tomato, pollination, Jordan, plastichouse, greenhouse.
o maximize fruit set in tomatoes and other crops,
plant growth bioregulator (PGB) (Pak and
Kim,1999), plant or truss vibration, honeybees
(Kremen, 2001) and bumblebees (Paydas et al., 2000)
are frequently used. Nelson and Richard (1989) found
that electrical vibration is not practical and also tedious.
Recently, a worldwide trend is to use the bumblebee as
a pollinator on many crops including tomatoes due to
yield increase and enhancement of fruit quality
(Delaplane, 1995). Proporato et al. (1993) used bumblebees
for the pollination of tomatoes under polyethylene
tunnels and found that plants gave better yield and
quality fruits. In France, bumblebees colonies were
used in tomato pollination and gave more effective
pollination than mechanical vibration (Caudal and
Trapateau, 1992). Ikeda and Tadauchi (1995) found
that tomato fruits obtained by bumblebee pollination
were more uniform and contained more seeds, flesh,
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AL-ATTAL, KASRAWI, AND NAZER
22
acids and vitamin C contents than that obtained by
plant growth bioregulator application.
Tomato (Lycopersicon esculentum Mill) is planted in
the Jordan valley under plastichouses (i.e. greenhouses)
during the months of October, November and December
(Anonymous, 1998). Therefore, fruit set, fruit
development and even maturity of several clusters
occur during the cool climate in winter. Efficient
pollination and successful fertilization of greenhouse
tomato is needed to ensure maximum fruit set and the
proper development of high quality fruits, specially
during cool conditions (Dogterom et al., 1998; Ravestijin
and Sande, 1991).
Although tomato flower is self fertile, the structure
of the anther core, it’s mode of dehiscence and the
position of the style make some form of disturbance
necessary to ensure adequate pollination in cool winter
or in high summer temperatures (Raymond, 1985;
Rylski et al., 1994). Banda and Paxton (1991) found
that fruit setting of tomatoes grown in greenhouses is
frequently poor and fruit set is very dependent on the
use of mechanical aids.
The objective of this research was to compare
three pollinating techniques, bumblebee, PGB and
vibration, with respect to fruit set, yield, and fruit
quality in greenhouse tomatoes.
Materials and Methods
All treatments were performed in two neighboring
greenhouses in the Abu-Ubiedah area in the Jordan
valley. No control on light, temperature or relative
humidity inside the greenhouses was performed.
“Argenta”, a common long shelf life cultivar of
greenhouse tomatoes used for exporting purposes was
transplanted on the 10
th
of November 1996.
Both greenhouses were identical and were 60 m
long, 8 m wide, grown with 5 raised beds of tomatoes.
The width of each bed was 0.5 m. Two rows were
planted in each bed and the distance between the beds
was 1m. The space within rows in beds was 30 cm and
between rows was 20 cm. Beds were covered with
black polyethylene plastic mulch and plants were
irrigated by drip irrigation system.
The first 20 m, the last 20 m of raised beds, and
beds on both sides of the greenhouse were excluded
from the experimental area to decrease variation among
plots. A randomized complete block design with three
replicates was used.
Each bed (which includes two rows) was divided
into three plots and each plot was randomly assigned to
each treatment. In greenhouse B, the PGB, the vibration
and control treatments were conducted, while in
greenhouse A, the treatment was only bumblebee. In
both greenhouses, the number of plants in each plot was
10. At random, from the 10 plants in each plot, 4 plants
were labeled for yield measurement (productivity
plants), three plants were used for quality parameter
evaluation (quality plants) and three for substitution.
Temperature and relative humidity were recorded each
day by a thermo-hygrograph and minimax thermometer.
A bumblebee hive, with an estimated 80 workers,
was placed inside the greenhouse (A) on 10 December
and removed on 1 April with the termination of
flowering clusters. The hive was placed for 24 hrs in
the experimental greenhouse, then removed and
returned after 48 hrs.
The PGB (para-chlorophenoxyacetic acid 7 gm/l.
4-CPA) was used in the PGB application treatment.
The PGB was diluted by taking the proper amount from
the stock solution in one liter of tap water according to
the label instructions. Three ml from the stock were
applied when the temperature was lower than 20°C and
2 ml when the temperature was more than 20°C. The
application was done by using a hand sprayer of 1 L
volume. One spray was applied on each flower cluster.
Spraying was carried out in synchronization with
flower anthesis. Twenty-one sprays were applied
between 10 December 1996 and 1 April 1997.
In the vibration treatment, plants were hand
vibrated each day in the morning between 10-11 a.m.
for 3-5 seconds. The control plants were not treated.
Vibration was performed between the 10
th
of December
and the 1
st
of April.
Fruit set percentage was calculated in each flower
cluster in the productivity labeled plants in each plot
until the end of fruit set on the 11
th
cluster. At maturity,
fruits of the first nine flower clusters were harvested
and average fruit weight and total yield for each cluster
were recorded.
At harvesting, size, weight, specific gravity,
firmness of fruit, and number of seeds per fruit were
measured. For fruit quality, fruit numbers 1, 3, and 5
from cluster number 1,3, and 5 on each of the three
quality labeled plants were assigned. Fruit size was
determined by the water replacement method, then the
specific gravity of the fruit was computed, the total of
81 fruits was measured.
Seed extract was made from fruit number 3 of
cluster numbers 1, 3, and 5 for each quality labeled
plants. The number of seeds inside each fruit was
counted. A total of 27 fruits was used to measure this
parameter in each treatment.
A fruit pressure tester was used to measure flesh
firmness in fruit number 1 of clusters 1,3, and 5 of
quality plants. Testing began by removing the
epidermal layer of tomato fruit with a sharp knife on
the two opposite sides, then flesh firmness was
measured and the average of two readings was
calculated. A total of 27 fruits was tested in each
treatment.
Results and Discussion
Y
IELD
: Bumblebee pollinated tomato flowers produced
significantly the highest average fruit weight and yield per
INFLUENCE OF POLLINATION TECHNIQUE ON GREENHOUSE TOMATO PRODUCTION
23
TABLE 1
Yield per plant, fruit weight, fruit size, seed number, firmness, and specific gravity in the bumblebee, plant growth
bioregulator (PGB), vibration and control treatments of greenhouse tomatoes.
Treatment
Parameter Bumblebees PGB Vibration Control
Average yield per plant (g) 5132.20a* 4116.80b 3591.00c 2818.50d
Average fruit weight (g) 100.30a 80.50b 84.10b 70.60c
Average fruit size (cm
3
) 99.30b 108.40ab 126.80a 98.50b
Average seed number per fruit 177.00a 61.80c 86.10b 89.80b
Firmness (Kg/cm
2
) 3015.80a 2690.00ab 2846.10ab 2464.40b
Average fruit specific gravity (g/ml) 1.03a 0.96b 0.983b 0.95c
* Numbers having same letters in the same row are not significantly different at p = 0.05 according to Duncan Multiple Range Test.
plant than the other treatments. The lowest average fruit
weight and the lowest yield per plant were produced from
the control tomato plants (Table 1) (Figure 1). Paxton and
Banda (1991) found that the bumblebee pollination is the
best means of pollination regarding the tomato yield per
plant. Ikeda and Tadauchi (1995) reported that the use of
bumblebees gave a higher yield than the application of
PGB. However, Fiume and Parisi (1994) found that PGB
application is slightly better than bumblebee pollination
in tomato. This yield increase is due to higher number of
pollen grains that fertilize the ovules and consequently
the higher number of seeds per fruit that contributed to a
higher fruit weight.
The temperature throughout the flowering, growth
and fruit development stages ranged from 2-14
o
C at
night to 17-42
o
C during the day. This high fluctuation
in temperature, the low night temperature at the stage of
flower formation, in addition to stigmatic elongation on
hot days will lead to poor fruit set in both vibration and
control treatments. This could be related to poor
pollination or poor fertilization. In the bumblebee
treatment, buzz-pollination will overcome stigmatic
elongation. Bumblebees visit a high number of flowers
each day. This increases the possibility of transferring
viable pollen. Also, a high relative humidity in winter
days makes pollen clump. As a result no transfer of
pollen grain to the stigma occurs in both the control and
vibration treatments. In several clusters in the PGB
treatment many fruits were seedless indicating that
PGB application induces fruit set. This takes place
regardless of the climatic conditions. Consequently
these fruits will have a lower density. One or more of
these factors may play a role in the difference between
the effect of the treatments over each cluster.
A
VERAGE
Y
IELD AND
F
RUIT
S
ET
(C
LUSTER
W
ISE
A
NALYSIS
): In general, the average cluster yield and
fruit weight were significantly higher in the bumblebee
treatment than the other treatments. However, in some
clusters there were no significant differences via the
treatments or the significance was between the
treatments and the control only.
Figure 1. Average number of greenhouse tomato flowers per plant during the flowering period.
AL-ATTAL, KASRAWI, AND NAZER
24
TABLE 2
Average fruit weight and yield per tomato plant in the bumblebee, plant growth bioregulator (PGB), vibration and control
treatments cluster wise analysis.
Bumblebee PGB Vibration Control
Cluster Average
fruit Average
yield Average
fruit Average
yield Average
fruit Average
yield Average
fruit Average
yield
1 93.0a* 619.6a 88.2a 428.7b 91.4a
278.7bc
70.8a 192.0c
2 111.1a 630.3a 78.9ab 495.0ab 89.8ab
351.2bc
75.6c 244.1c
3 97.1a 652.3a 84.7a 463.7b 88.2a
374.2bc
71.1a 312.3c
4 93.3a 578.8a 80.0ab 483.3ab 79.8ab
516.0ab
70.3c 399.0c
5 110.0a 607.8a 82.5b 534.5ab 85.6b
590.8ab
78.3b 445.0c
6 108.2a 689.3a 76.3b 489.5ab 90.8bc
495.0b
66.2c 374.3b
7 100.6a 633.0a 73.3b 434.3b 85.6c
345.0b
64.4d 271.5b
8 94.5a 650.0a 73.6b 418.0b 70.5b
316.9b
66.8b 287.0b
9 95.1a 650.0a 86.6a 369.8b 75.6b
323.0b
71.5b 283.3b
Average fruit (g) 100.3a - 80.5b - 84.1b
-
70.6c -
Average plant yield (g) - 5132.2a - 4116.8b -
3591.0c
- 2818.5d
* Numbers having same letters in rows for the same parameter are not significantly different at P=0.05 according to Duncan Multiple Range Test.
According to the climatic conditions throughout the
flowering period, as in cluster four, the vibration
treatment was significantly higher than the PGB (Table 2)
(Figure 2).
The overall average fruit set by the bumblebee
treatment was (99.1 %) with no significant difference
with that of PGB treatment (96.7 %). Both bumblebee
and PGB treatments gave significantly higher fruit set
percentage than the vibration (76.5 %) and the control
(65.3 %) (Table 3).
In the first, second, seventh, and eighth clusters,
the average fruit set in all clusters was similar in the
bumblebee and PGB treatments. Both were
significantly higher than vibration and control
treatment. In the third cluster, there was no significant
difference in fruit set among treatments, but all were
higher than the control. In the fourth and ninth clusters,
fruit set in all treatments was not significantly different,
but the bumblebee and the PGB application gave
significantly higher fruit set than the control. In the fifth
and sixth clusters, there were no differences in fruit set
percentage between the treatments and the control. In the
tenth cluster, the bumblebee treatment and the
bioregulator application were not significantly different
but they gave higher fruit set than the vibration. Also,
the vibration was higher than the control. In the eleventh
cluster, bumblebee treatment ranked first in fruit set
percentage, than the PGB application and vibration
while the control was the least with no significant
difference between all treatments. The low fruit set in
the vibration and the control treatments in the first and
the second cluster may be due to poor pollination and to
poor fertilization in cool nights (2-14
o
C) and to high
day temperature (31-42
o
C). During the fruit set period
of cluster three, the average night temperature was 12
o
C
and day temperatures was 31
o
C. This gave good
pollination in all treatments and the control resulting in
good fruit set. In the seventh and eighth clusters the day
temperature had risen to 38
o
C and induced stigmatic
elongation. In the ninth, tenth and eleventh clusters fruit
set in the vibration treatment, decreased significantly
due to a high day temperature (38
o
C), and to the fact
that in this period of growth, the plants were near the
plastic sheets which cause stigmatic elongation.
Figure 2. The date of anthesis of tomato clusters 1-11 in 0.5 dunum greenhouse in 1996.
INFLUENCE OF POLLINATION TECHNIQUE ON GREENHOUSE TOMATO PRODUCTION
25
TABLE 3
Average fruit set percentage in greenhouses tomato pollinated bumblebees, plant growth bioregulator (PGB), vibration and
control treatment.
Treatment
Cluster Bumblebee
(%) Plant Growth Bio
Regulator (%) Vibration
(%) Control
(%)
1
100.0a* 97.8a 73.9b 63.1b
2
100.0a 98.1a 73.3b 64.6b
3
98.7a 94.0a 89.6a 70.9b
4
100.0a 98.0a 91.2ab 75.3b
5
100.0a 99.3a 89.8a 82.6a
6
100.0a 93.0a 74.1a 78.0a
7
99.5a 94.3a 54.8b 51.0b
8
94.4a 94.9a 63.9b 52.0b
9
98.5a 99.3a 75.6ab 54.1b
10
99.7a 97.8a 78.7b 61.5c
11
95.1a 86.6ab 75.6bc 71.5c
Average 99.1a 96.7a 76.5b 65.3c
* Numbers having same letters are not significantly different at P=0.05 according to Duncan Multiple Range Test.
In the bumblebee treatment, it seems that the
bumblebee individual usually carries viable pollen
grains which gives better yields than the PGB under
temperature between (2-14
o
C) at night and (17-42
o
C)
during the day.
Q
UALITY
P
ARAMETERS
: There was a significant
difference in the average fruit weight between the
different treatments (Table 1). Regarding fruit size,
there was no significant difference between the fruit
size in the bumblebee, PGB and the control treatment.
The largest fruit size was in the vibration treatment,
126.8 ml, followed by PGB, 108.4 ml. The bumblebee
and control treatment gave the least fruit size, 99.3 ml,
and 98.5 ml, respectively (Table 1).
Fruit density in the bumblebee treatment was
significantly higher than other treatments. There was no
significant difference between the PGB and vibration
treatments. The least dense fruits were in the control.
PGB does not increase cell division in tomato, but the
increase in size is related to cell elongation, that
resulted in many cavities and lighter fruits. In the
vibration and control treatments density was correlated
with the number of seeds (Table 1).
Regarding the firmness of the fruits, the bumblebee
treatment gave the hardest fruits, while the PGB
treatment and vibration gave intermediate results. The
control fruits were the least firm (Table 1).
Seed number per fruit was significantly higher in
the bumblebee treatment (177.0). The lowest seed
number was in the PGB treatment (61.8). There was no
significant difference in the number of seeds between
the control and the vibration treatments 89.8 and 86.1,
respectively (Table 1).
The large tomato fruit size from PGB treatment
was related to the effect of the bioregulator on cell
elongation but with very low seed number inside the
fruit. The vibration treatment produced low fruit set and
lower number of fruits per cluster and plant, which may
be compensated for by the larger size.
The lower number of seeds per fruit was for the
vibration and control treatments. The bumblebee
individual has a special buzzing pollination tactic. This
ensures more contact between the pollen grains on the
stigma. In the control, apparently the same number of
pollen grains will fertilize the ovule due to deliberate
vibration to increase fruit set and to workers movement
and wind circulation. This of course was not as efficient
as the buzzing effect of bumblebees. Paxton and Banda
(1991) have similar results, i.e, that bumblebees
resulted in fruits with higher number of seeds, and
higher weight than the vibration or the control. Vecchio
et al. (1996) found that the application of PGB will
speed up the ripening of fruits by about one week.
S
HAPE OF THE
F
RUITS
: Flowers pollinated by
bumblebees gave fruits that looked better in shape and
were plump without puffiness, had more seeds, and a
higher specific gravity, were harder, and were uniform
color. These characteristics make fruits more preferable
for local and export markets. Plants that were treated
with PGB produced puffy, soft fruits, with relatively
lower specific gravity than other treatments, and the
color some times is not uniform. In the vibration
treatment, the fruits are plump but usually the size was
larger than the others with a lower number of seeds as
compared to the fruits from the bumblebee treatment.
Fruits of the control were smaller than those in the
other treatments.
Conclusions
The results indicated that bumblebees could be
used successfully in greenhouses for tomato plant
AL-ATTAL, KASRAWI, AND NAZER
26
pollination. Bumblebee-pollinated tomatoes gave
higher yield, higher number of seeds, better weight-size
correlation, higher specific gravity and higher fruit
firmness than other pollinating agents; plant growth
bioregulator and plant vibration.
Acknowledgement
The authors express their gratitude to the Deanship
of Scientific Research at Jordan University for the
partial financial support of this research. Sincere thanks
are extended to Mr. Khalil Abu-Ghannam for his offer
to conduct this research at his farm and for his valuable
suggestions and help through out the study. The
comments and the revision of the article by Dr.
Valkmar Hasse is greatly acknowledged.
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_______________________________________________________
Received July 2002.
Accepted Jan 2003.
