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

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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