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SEX EXPRESSION AND FRUIT SET MODIFICATION OF PICKLING CUCUMBER (Cucumis sativus L.) BY GIBBERELLIC ACID
Joan F. Agustin and Dr. Justo G. Canare Jr
ABSTRACT
The study was conducted to determine the growth and yield response of pickling
cucumber to GA3 concentration ,with emphasis on sex expression and fruit set.
The experiment was set up following RCBD with four replications. The
treatments were T1-0 ppm (control), T2-50 ppm, T3-100 ppm, T4-200 ppm, T5-300 ppm.
Treatment 2 (50 ppm) produced the highest average number of female flower,
female flower to male ratio and average number of ruits. Lowest number of female
flower, female flower to male flower ratio and average number of fruits were produced in
untreated plants (T1-control).
INTRODUCTION
The cucumber (Cucumis sativus L.) belongs to family Cucurbitaceae. It is an
annual herbaceous crop with a vining type of growth, which results from the branching of
the main stem into several trailing laterals. It is a monoecious plant that is cultivated for
its immature fruits. The male flowers have very short stems borne in clusters of three to
five. These are located mostly on the main stem, while female flowers are located on the
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laterals as well as the main stem and can be recognized by the ovary at the base of the
flower, which will develop into fruit.
Cucumber, a monoecious crop, produces more male flowers than female flowers,
which affects the yield of cucumber. If the female to male flower ratio and the fruit set
can be increased, the chance of more fruits being produced would also be increased. This
advantage is more pronounced in pickling cucumber than in table cucumber because the
fruits are harvested when still small and harvesting is more frequent.
Gibberellic acid occurs naturally in the seeds of many species and is produced
commercially by growing Gibberella fujikoroi fungus cultures in vats, then extracting
and purifying the GA3. Gibberellins were discovered by Japanese plant pathologists
studying “bakanae” disease (“foolish seedling”) of rice, in which seedlings grow
elongated and die. In 1998, Shotoro Hori demonstrated that it was caused by a fungus,
now known as Gibberella fujikoroi. In 1935 Teijiro Yabuta first isolated a non-crystalline
solid and named it Gibberellin. In 1938, Yabuta and Yusuke Sumiki first isolated a
crystalline compound from the cultured fungus (Takahashi et al., 1991).
Objective of the Study
The objective of the study is to determine the growth and yield response of
pickling cucumber to GA3 concentration, with emphasis on sex expression and fruit set.
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METHODOLOGY
Cultural Management Practices
The cucumber variety Ambassador seedlings were raised in seedling trays with
mixture of 1:1:1 ratio of garden soil, organic fertilizer.
The experimental area was prepared using a rotavator until the soil was
pulverized. After thorough land preparation, the area was divided into four blocks
representing the replications. Each block was further subdivided into five plots, each
measuring 3 meters long and 1 meter wide. Seedlings were transplanted at the age of 13
days at a distance of 50 cm.
A GA3 commercial product with a concentration of 10% was sprayed at 14 days
after transplanting. Plants were sprayed up to point of runoff. Other plants in adjacent
plots were covered by plastic while spraying to prevent contamination.
Pruning was done 16 days after transplanting removing leaves 50 cm above the
ground (mostly 3-5 leaves). At 20 days after transplanting, unproductive branches were
also removed. Pruning of branches was done regularly leaving only the main branch.
Training was done vertically using string at 12 days after transplanting.
For fertilizer management, three granules of complete fertilizer covered with soil
were applied in each hole before sowing one seed per hill. At 6 days after sowing, 3
grams of potassium nitrate was applied each seedlings. For transplanted seedlings,
Potassium Nitrate was applied following the rate of 116kg/ha at 7 days, 21 days, 28,35,
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42, 49, and 63 days after transplanting and complete fertilizer at a rate of 300kg/ha at 7
days, 14 days, 21 days, 28, 35 and 42 days after transplanting
For proper growth and development, irrigation was done when the plants showed
sign of wilting or at five days interval depending upon the occurrence of rainfall.
Hand weeding was done regularly to keep the area clean and to prevent weed
competition.
Cucumbers were protected from the attack of pests like leaf miners and aphids by
spraying hot pepper with water. Application was done 30 and 40 days after transplanting.
Gherkins 3 inches long were harvested every day in the morning and late
afternoon and everyday thereafter for a period of one month.
Data Gathered
The following data were gathered in this study: days to flowering, days to first
harvest, average number of flowers per plant, average number of male flowers per plants,
average number of female flowers per plant, female flower to male flower ratio, average
number of fruits per plant, percent fruit set and weight of fruits in grams.
The data collected were organized, tabulated and analyzed using the Analysis of
Variance (ANOVA) of Randomized Complete Block Design (RCBD). Treatment means
were compared using Duncan’s multiple range test (DMRT).
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RESULTS AND DISCUSSION
Days to Flowering and Days to First Harvest
The untreated plants flowered significantly earliest at 32 days compared to all
plants treated with GA3, which flowered from 38 to 43 days (Table 1). Plants sprayed
with 50 ppm GA3 flowered significantly earlier than those sprayed with 200 ppm and 300
ppm GA3, while plants sprayed with 100 ppm GA3 flowered significantly earlier than
those sprayed with 300 ppm GA3. Other pairs of means were not significantly different.
Table 1. Days to flowering and days to first harvest as influenced by different
concentrations of GA3.
TREATMENT DAYS TO FLOWERING DAYS TO FIRST HARVEST
T1 – Control 32 a 51 a
T2 – 50 ppm 38 b 57 b
T3 – 100 ppm 39 bc 60 bc
T4 – 200 ppm 40 c 63 c
T5 – 300 ppm 43 d 68 d
Means followed by the same letter are not significantly different using DMRT at 5% level
The general trend was that flowering was delayed as GA3 concentration increased.
This agrees with the findings of Levitt (1969) that application of GA3 delayed flowering
due to continuous cell enlargement and stem elongation.
The number of days to first harvest as influenced by different concentrations of
GA3 shows that untreated plants exhibited the shortest days to first harvest with a mean
of 51 days. This was followed by plants from Treatments 2, 3, and 4 with means of 57,
60, and 63 days, respectively. Plants from Treatment 5 (300 ppm) were observed to have
the longest days to first harvest with a mean of 68 days.
Comparison among means shows that T1 (control) had the significantly shortest
number of days to first harvest (51 days), while plants treated with highest concentration
of GA3, T5 (300 ppm), had the significantly longest days to first harvest ( 68 days).
This is similar to the findings of Castañeda (1998) that application of different
concentrations of GA3 prolongs the growth of the crops, resulting to late harvesting.
Furthermore, the trend of days to first harvest was exactly similar to the trend of
days to flowering. This indicates that days to flowering is related to days to first harvest.
Average Number of Flowers per Plant
Table 2 shows the average number of flowers per plant as influenced by different
concentrations of GA3. It shows that untreated plants have the highest average number of
flowers per plant with 44 flowers, followed by T2 (500 ppm), T3 (100 ppm) and T4 (200
ppm) with means of 38, 36, and 36, respectively. T5 (300 ppm) had the lowest average
number of flowers per plant with 33.
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Comparison among means shows that untreated plants produced significantly
more flowers per plant than those treated with 100 ppm, 200 ppm, and 300 ppm GA3,
which had comparable number of flowers per plant. However, plants treated with 50 ppm
GA3 had comparable number of flowers as the control plants.
Table 2. Average number of flowers per plant as influenced by different concentrations of GA3
TREATMENTS
AVERAGE NUMBER OF
FLOWERS PER PLANT
AVERAGE NUMBER OF
MALE FLOWERS PER PLANT
AVERAGE NUMBER OF FEMALE
FLOWERS PER PLANT
T1 – Control 44 a 40 a 3.8 b
T2 – 50 ppm 38 ab 31 b 6.5 a
T3 – 100 ppm 36 b 28 b 8.0 a
T4 – 200 ppm 36 b 28 b 7.2 a
T5 – 300 ppm 33 b 26 b 6.8 a
Means followed by the same letter are not significantly different using DMRT at 5% level
The results indicate that the concentration 50 ppm of GA3 was too low to have an
effect on number of flowers. However, GA3 concentrations of 100 ppm and above
depressed flowering of cucumber.
The average number of male flowers per plant as influenced by different
concentrations of GA3 revealed that untreated plants obtained the highest number of
male flowers per plant followed by T2 (50 ppm), T3 (100 ppm), and T4 (200 ppm) with
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means of 31, 28, and 28, respectively. Meanwhile, T5 (300 ppm) obtained the fewest male
flowers per plant with 26.
Comparison among means revealed that plants treated with GA3 had significantly
fewer male flowers than untreated plants, while they had comparable numbers of male
flowers.
The results imply that GA3 reduces both the total number of flowers and the
number of male flowers. It can also be noted in both average number of flowers and
number of male flowers per plant, that numerically, the results showed a decreasing
number of male flowers relative to increasing concentration of GA3.
The reduction in male flowers was brought about by an increase in femaleness as
will be shown in the next section. Riley (1990) reported that formation of the male flower
is generally promoted by concentrations of 10-20 ppm and female flowers by
concentrations of 200-300 ppm, while Bautista et al. (1983) reported that GA3 used at
concentrations from 100-240 ppm were found adequate to effect a shift in sex expression
to femaleness.
It is apparent in this study that femaleness was promoted at the expense of male
flowers.
The average number of female flowers per plant as influenced by different
concentrations of GA3 shows that 100 ppm obtained the highest number of female flower
with a mean of 8.0 flowers followed by 200 ppm with a mean of 7.2 flowers and 300 ppm
(6.8 flowers). The lowest number of female flower was noted from the untreated plant
with a mean of 3.8 flowers.
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Comparison among means revealed that plants treated with GA3 produced
significantly more female flowers than untreated plants. Meanwhile, all GA3-treated
plants had number of female flowers that were comparable.
The results corroborated previous findings (Bautista, et al, 1983; Riley, 1990;
Leopold and Kriedemann, 1990) that GA3 can induce femaleness. However, the
concentrations at which femaleness is promoted differed. While Bautista et al (1983) and
Riley (1990) said that formation of female flowers is promoted at GA3 concentrations of
100-300 ppm, this study showed that even the low concentration of 50 ppm promoted
femaleness.
Furthermore, the low number of female flowers per plant was brought about by
pruning out of lateral branches leaving only the main stem to avoid shading effect.
Female Flower to Male Flower Ratio
Table 3 presents the female flower to male flower ratio as influenced by different
concentrations of GA3. Observation revealed that untreated plants had the lowest female
to male flower ratio with a mean of 0.09, followed by T2-50 ppm, T4-200 ppm, and T5-
300 ppm and T3-100 ppm with means of 0.21, 0.25, 0.26, and 0.28, respectively.
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Table 3. Female flower to male flower ratio as influenced by different concentrations of GA3
TREATMENT MEAN
T1 – Control 0.09 b
T2 – 50 ppm 0.21 a
T3 – 100 ppm 0.28 a
T4 – 200 ppm 0.25 a
T5 – 300 ppm 0.26 a
Means followed by the same letter are not significantly different using DMRT at 5% level
Comparison among means revealed that GA3 treatment significantly increased
female to male flower ratio. However, the female to male flower ratio of the GA3-treated
plants with concentrations of 50 ppm to 300 ppm were not significantly different.
The increase in female to male flower ratio in the GA3-treated plants was brought
about by the combination of reduced number of male flowers and increased number of
female flowers.
The female to male flower ratio of the control plants was comparable to that
reported by Tiedjens (1928) who stated that the ratio between staminate and pistillate
flowers in cucurbits is 10:1. On the other hand, the female to male flower ratio of the
GA3-treated plants was 2 to 3 times that of the control plants.
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Percent Fruit Set
Presented in Table 4 is the percent fruit set as influenced by different
concentrations of GA3. Results revealed that (T5) 300 ppm and T4 (200 ppm) gave the
highest fruit set with a mean of 99 %, followed by T3 (100 ppm) and T2 (50 ppm) with
means of 98 % and 94 %, respectively. Untreated plants were observed to have the lowest
percent fruit set of 90 %.
Table 4. Percent fruit set as influenced by different concentrations of GA3
TREATMENT MEAN
T1 – Control 90
T2 – 50 ppm 94
T3 – 100 ppm 98
T4 – 200 ppm 99
T5 – 300 ppm 99
Although GA3 is known to promote fruit set (Taiz and Zeiger, 1998; Riley, 1990),
the effect was not demonstrated in this study. This could be due to the low number of
female flowers per plant produced in the study. It can be noted, however, that there was a
numerical increase in percent fruit set as GA3 concentration increased.
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Average Number of Fruits per Plant
Table 5 shows the average number of fruits per plant as influenced by different
concentrations of GA3. Observation revealed that plants sprayed with 100 ppm of GA3
gave the highest number of fruits per plant with a mean of 7.9 fruits, while the untreated
plants (T1) produced the lowest number of fruits with a mean of 3.1 fruits. This was
followed by T2 (50 ppm), T4 (200 ppm) and T5 (300 ppm) with means of 6.1, 6.9, and 6.9
fruits, respectively.
Comparison among means revealed that GA3-treated plants had significantly more
marketable fruits per plant than untreated plants. Among the GA3-treated plants, numbers
of marketable fruits per plant were comparable.
Table 5. Average number of fruits per plant as influenced by different concentrations of GA3
TREATMENT MEAN
T1 – Control 3.1 b
T2 – 50 ppm 6.1 a
T3 – 100 ppm 7.9 a
T4 – 200 ppm 6.9 a
T5 – 300 ppm 6.9 a
Means followed by the same letter are not significantly different using DMRT at 5% level
Small number of deformed fruits was observed in which out of 20 plots, only 7
had deformed fruits.
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The trend of number of marketable fruits per plant was similar to that of number
of female flowers per plant. Since fruits develop from female flowers, this suggests that
the increase in number of marketable fruits per plant of GA3-treated plants was brought
about by the increase in number of female flowers per plant.
Again, same with the results in the number of female flowers per plant, the low
response to GA3 was attributed to the pruning out of lateral branches leaving only the
main stem to avoid shading effect.
Weight of Fruits Per Plant (g)
Table 6 shows the weight of fruits per plant as influenced by different
concentrations of GA3. It can be noted that plants treated with GA3 produced the heaviest
fruit. Application of 100 ppm of GA3 gave the heaviest fruit with a mean of 217 grams
followed by 200 ppm (T4), 300 ppm (T5), and 50 ppm (T2) with means of 194, 189, and
168 grams, respectively. Untreated plants have the lightest weight with a mean of 84
grams.
Table 6. Weight (g) of fruits per plant as influenced by different concentrations of GA3
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TREATMENTREPLICATION
MEANI II III IV
T1 – Control 103 69 72 94 84 b
T2 – 50 ppm 156 145 193 179 168 a
T3 – 100 ppm 195 259 236 177 217 a
T4 – 200 ppm 225 168 180 204 194 a
T5 – 300 ppm 223 142 167 224 189 a
Means followed by the same letter are not significantly different using DMRT at 5% level
Treatments 2 to 5 had means that were comparable. Results revealed that
application of GA3 significantly increased the weight of fruits compared to control plants.
The results could be attributed to the number of fruits from each treatment since the fruits
were harvested when they reached a certain length.
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SUMMARY AND CONCLUSION
This study was conducted to determine the response of pickling cucumber (cv
Ambassador) to different concentrations of GA3. The different concentrations were
applied at 14 days after transplanting with the following treatments: T1-0 ppm (control),
T2-50 ppm, T3-100 ppm, T4-200 ppm and T5-300 ppm. The study was conducted in a
greenhouse using randomized complete block design (RCBD) with four replications.
The study revealed that GA3 increased number of female flowers, female to male
flower ratio, number of fruits and weight of fruits. It delayed flowering and first harvest
and reduced number of flowers per plant and number of male flowers per plant. Finally, it
had no effect on percent fruit set.
Vine length at first and final harvest increased with GA3 concentration up to 200
ppm but was reduced to the 50 ppm level at 300 ppm. Number of flowers per plant was
reduced by GA3 concentrations of 100 ppm and above, but not by 50 ppm. However,
number of male flowers was reduced by all GA3 concentrations, although the reduction
was comparable in all GA3 concentrations.
Number of female flowers, female to male flower ratio, number of fruits, and
weight of fruits were increased by GA3 concentration in the same way. The four GA3
concentrations had comparable effects.
The desirable response to GA3 concentration was up to the lowest concentration
of 50 ppm only. Under the conditions of this study, the higher concentrations of 100 ppm
to 300 ppm did not give any advantage over 50 ppm.
LITERATURE CITED
AUDUS, L.J. 1965. Plant growth substances. Interscience Publisher, New York. 125p.
BAUTISTA,O.K., H.V. VALMAYOR, P.C. TABORA, JR., R.V. C. ESPINO.1983 Introduction to tropical horticulture. Department of Horticulture, College of Agriculture, UPLB. 220p.
CASTAÑEDA, W.P.1998. Gibberellic Acid Increases Garlic Yield. D.A. PCCARD. 60p.
LEVITT, K.J. 1969. Gibberellic acid in plants. McGraw-Hill Book Company, New York.170p.
LEOPOLD, A.C and P.E. KRIEDEMAN. 1990. Plant growth and development. 3 rd ed. McGraw-Hill Book Company, New York, USA. 545p.
RILEY, E. H. 1990. Introductory horticulture . Denmar Publisher, New York .320p.
TAIZ, L. and E. ZEIGER. 1998. Plant Physiology. Sinauer Associates, Inc., Massachusetts, U.S.A.
TAKAHASHI, P. and J. MACMILLAN. 1991. Gibberellins. SpringerVerlag, New york.220p.
TIEDJENS, V.A. 1928. Sex ratios in cucumber flowers as affected by different conditions of soil and light. McGrawHill Book Company, New York
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