Abstract: The experiment was conducted to study the effect of plant growth regulators and their time of spray on morphology, yield and yield contributing characters of soybean. Plants of soybean Cv. PB-1 were sprayed three times (T1 = spray at 15 DAS, T2 = spray at 30 DAS and T3 = spray at 45 DAS) with two concentrations (100 and 200 ppm) of gibberellic acid (GA3) and maleic hydrazide (MH). Significant variations exist among the concentrations of growth regulators and with their time of application in respect of morphological, yield and yield contributing characters of soybean. T2 followed by T3 produced the tallest plant with the highest number of branches, leaves, flowers, pods per plant, number of seeds per pod, seed yield per plant, 100-seed weight and seed yield (t ha-1). T1 produced the least of them. GA3 was more effective than MH. GA3 at 100 ppm followed by GA3 at 200 ppm produced the highest number of branches, leaves, flowers, pods per plant, number of seeds per pod, seed yield per plant, 100-seed weight and seed yield (t ha-1) while 200 ppm MH was least effective to produce them. The present study clearly shows that almost all the plants treated with growth regulators performed better than control. However, interaction effect indicated that 100 ppm GA3 treated plants sprayed at 30 DAS (T2C3) showed the best performance.
INTRODUCTION
Soybean is one of the most important economic food legumes cultivated world wide because of its higher nutritional and industrial values. It is an introduced crop in Bangladesh and usually used as ingredient of poultry, dairy and fish feeds. The multipurpose use of soybean is gradually increasing in our country. Besides oil, soybean seeds are used for producing many of the foods like soya-milk, soya-dal, soya-curd, soya-flour, soya-khichuri, soya-chatni, baby food, confectioneries and roasted soybean snacks which are becoming familiar to the people of Bangladesh. Soybean contributes more than 41% of the total oil seed production of the world[1]. According to the planning commission of the People's Republic of Bangladesh, about 1,82,000 tons of edible oil is necessary every year whereas the indigenous production is only 54,990 tons[2]. Under this circumstances, a large amount of foreign currency is being spent every year for buying the deficit amount of oil. So, it is essential to increase soybean cultivation in Bangladesh.
In Bangladesh, among all the oil seed crops, mustard tops the list in terms of area, while soybean is treated as such a very minor pulse and oil crop concentrated only in few districts and locations that the reference of soybean does not appear in the regular national statistics. The statistical information is rare regarding production and acreage of soybean in Bangladesh. It was estimated to cover about 5000 hectares with approximately 7500 tons of production all over the country in 1997[3]. Research and extension works on soybean have been started in 1972-73 by Mannonite Central Committee and subsequently by Bangladesh Agricultural Research Council. But still the yield of soybean here is very discouraging compared to other soybean producing countries. This is mainly due to the use of low yield potential varieties and poor cultivation techniques, especially due to lack of knowledge about modern production technique i.e., lack of judicious application of irrigation water, fertilizer, growth regulators etc. GA3 and MH are two plant growth regulators which can manipulate a variety of growth and developmental phenomena in various crops. Foliar application of GA3 has been found to increase stem diameter, promote stem elongation and leaf formation, accelerated flowering, increase the length of the flower stalk and number of flowers or inflorescence[4] as well as total yield[5-7]. It was also reported that soybean yield was increased by the application of MH[8].
Studies in other countries of the world provided useful information regarding the use of growth regulators on soybean. Unfortunately, very limited works have been carried out in Bangladesh in this regard. Studies on the effects of growth regulators in our climatic condition could provide useful information. Therefore, the present work was designed to study the influence of GA3 and MH on the morphological and yield contributing characters of soybean and to know the most suitable time of spraying of growth regulators to improve its production.
MATERIALS AND METHODS
The experiment was conducted at the field laboratory of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, during the period from December, 2001 to March, 2002. A single variety of soybean (Glycine max L. Cv. PB-1) was used in the present study. The two-factor experiment {Factor A (growth regulators): C0 = Control, C1 = 100 ppm MH, C2 = 200 ppm MH, C3 = 100 ppm GA3, C4 = 200 ppm GA3 and Factor B (time of spray): T1 = 15 days after sowing (DAS), T2 = 30 DAS, T3 = 45 DAS} was laid out in split plot design with 4 replications. The size of the unit plot was 1x1 m and the distance between plots was 0.5 m. The plots were raised up to 15 cm from the soil surface.
The plots were fertilized with cowdung, urea, triple super phosphate (TSP), muriate of potash (MP) and gypsum @ 6 t ha-1, 50, 150, 100 and 80 kg ha-1, respectively. Total amount of cowdung, urea, TSP, MP and gypsum were applied as basal dose during land preparation. The seeds of soybean were sown on December 11, 2001 with a spacing of 20x10 cm and 2 seeds were placed in each point at 2-3 cm depth from the soil surface. At 15 DAS, seedlings were thinned to one per point. Intercultural operations were done as and when required.
Preparation and application of growth regulators: Plant growth regulators were prepared following the procedure mentioned below and spraying was done at noon by using a hand sprayer.
Gibberellic acid: A 100 ppm solution of GA3 was prepared by dissolving 100 mg of GA3 in a small quantity of ethanol prior to dilution with distilled water. Then distilled water was added to make the volume of 1 L to get 100 ppm solution. In a similar way, solutions of 200 ppm were prepared. An adhesive namely, tween 20 @ 0.01% was added (2 drops/100 mL) to each solution[9].
Maleic hydrazide: Solutions of MH were prepared in a similar process followed for the preparation of GA3 solutions.
Distilled water (control): A corresponding amount of ethanol was added to distilled water making the final volume 1 L for application to the control plants. The adhesive, tween 20 @ 0.01%, was added to the control one.
Crop sampling and data collection: The first crop sampling was done on 20 DAS and it was continued at an interval of 20 days till physiological maturity at 100 DAS. At the time of each harvest, three plants were selected randomly from each plot. The height of the plants was ascertained by measuring with a graduated scale placed from ground level to top of the leaves. Number of branches and leaves per plant were recorded separately at each harvest. Total leaf area of individual sample was measured by an electronic leaf area meter (LI 3000, USA). Yield and yield contributing characters like number of flowers, pods per plant, number of seeds per pod, seed yield per plant, 100-seed weight and seed yield (t ha-1) were also recorded. Data of the experiment were analyzed statistically and the differences between pairs of means were compared by DMRT.
RESULTS AND DISCUSSION
Morphological characters
Plant height: The effect of time of spray on plant height was found
significant at all sampling dates except at 20 and 100 DAS (Fig.
1). At all growth stages, T2 produced the tallest plant and the
shortest by the T1. T3 was intermediately effective to
enhance the height of the plant. Application of growth regulators influenced
the plant height significantly at all stages of growth except 20 DAS (Fig.
2). GA3 applied @ 100 ppm produced the tallest plants and the
shortest by control at all growth stages. The interaction effect between time
and growth regulators on plant height was significant at all growth stages (Table
1). The tallest plant was produced by T2C3 followed
by T2C4 and the shortest plant was found in T1C0.
100 ppm MH was found better to enhance plant height than 200 ppm.
The increase in plant height due to GA3 application might be due to its effect on elongation of internodes[10]. GA3-induced highest plant height was observed in soybean[6], okra[11], rice[12] and groundnut[13].
Number of branches per plant: Different times of spray showed significant differences in number of branches per plant except at 80 DAS (Fig. 3).
| Table 1: | Interaction effect of plant growth regulators and their time of spray on plant height of soybean at different days after sowing |
| Table 2: | Interaction effect of plant growth regulators and their time of spray on number of branches per plant of soybean at different days after sowing |
| Table 3: | Effect of time of spray on number of leaves per plant of soybean at different days after sowing |
| Table 4: | Effect of plant growth regulators on number of leaves per plant of soybean at different days after sowing |
| Table 5: | Interaction effect of plant growth regulators and their time of spray on number of leaves per plant of soybean at different days after sowing |
| Table 6: | Effect of time of spray on leaf area per plant of soybean at different days after sowing |
| Table 7: | Effect of plant growth regulators on leaf area per plant of soybean at different days after sowing |
| Table 8: | Interaction effect of plant growth regulators and their time of spray on leaf area per plant of soybean at different days after sowing |
| Table 9: | Effect of time of spray on yield and yield contributing characters of soybean |
| Table 10: | Effect of plant growth regulators on yield and yield contributing characters on soybean |
| Table 11: | Interaction effect of plant growth regulators and their time of spray on yield and yield contributing characters of soybean at different days after sowing |
| NS= Not significant, *,**, significant at 1 and 5% level, respectively. Figures in a column with same letter(s) do not differ significantly as per DMRT | |
At all growth stages, T2 produced the maximum number of branches followed by T3 and T1. However, the effect of T1 was statistically similar to that of T3. Figure 4 shows significant differences among the concentrations of growth regulators at 40, 60 and 80 DAS. 100 ppm GA3 produced the maximum number of branches followed by 200 ppm GA3. Growth regulators had the superiority over control in increasing the number of branches at all growth stages. The interaction effect between times and growth regulators on the number of branches was significant only at 60 DAS (Table 2). Maximum number of branches was found in T2C3 and the minimum was observed in the interaction between T1C0 indicating early spray (spray at 15 DAS) is least effecting to produce branches in soybean plant.
In the present study, both GA3 and MH had stimulatory effect on the number of branches per plant. GA3-induced higher number of branches was found in soybean[6]. MH-induced higher number of branches was also reported in fenugreek by Alagukannan and Vijayakumar[14].
Number of leaves per plant: Number of leaves per plant was recorded from 20 DAS to 100 DAS. Among the times of spray, T2 produced significantly higher number of leaves at 20, 40 and 60 DASs followed by T3 and T1 (Table 3). At 80 and 100 DAS, T2 also produced the maximum number of leaves per plant, however, the result was statistically not significant. The results revealed a significant variation in number of leaves due to the effect of growth regulators applied at different phenophases of soybean (Table 4). The treated plants generated significantly higher number of leaves per plant. At 100 DAS, 100 ppm GA3 induced maximum number of leaves (26.33) followed by 200 ppm (22.92) indicating that GA3 was better at lower level than its higher level. Control plants had the minimum number of leaves. Interaction effect between time of spray and growth regulators on the number of leaves was significant at 40, 60 and 100 DASs (Table 5). Non-sprayed control plants performed worst than the sprayed plants. At all growth stages, T2C3 produced maximum number of leaves followed by T2C4.
In this experiment, the treated plants generated significantly higher number of leaves per plant. Satheeshan and Mohan Kumaran[15] reported that 100 ppm MH increased the number of leaves in Costus speciosus. Similarly, GA3-induced higher number of leaves was reported in wheat[16], soybean[6], faba bean[17] and bell pepper[18].
| Fig. 1: | Effect of time of spray of growth regulators on plant height of soybean at different days after sowing. **, significant at 1% level |
Leaf area per plant: Effect of time of spray on leaf area per plant was significant only at 60 DAS (Table 6). T2 produced the maximum leaf area (268.87 cm2) followed by T3 and T1. However, T1 and T3 were statistically similar in effect. The effect of growth regulators on the leaf area was significant at different growth stages except 20 and 100 DASs (Table 7). All the growth regulators increased leaf area with the advancement of growth stages. At 100 DAS, 100 ppm GA3 produced the maximum leaf area per plant (577.05 cm2) followed by 200 ppm GA3 (556.38 cm2) and the minimum (412.16 cm2) was observed in the control. Interaction effect between the time of spray and growth regulators on the leaf area was significant only at 60 DAS (Table 8). At all growth stages, the maximum leaf area was found in T2C3 and the minimum was observed in the interaction between T1C0.
The results of the present experiment supports the findings of Naidu and Swamy[19]. Leaf area depends on the size and number of leaves. Therefore, the increase in leaf area due to the application of growth regulators might be due the increase in the number of leaves per plant in present experiment.
| Fig. 2: | Effect of plant growth regulators on plant height of soybean at different days after sowing. **, significant at 1% level |
Yield and yield contributing characters
Number of flowers per plant:
The total number of flowers per plant was counted in the field in individual
treatment for each time of application. The difference due to time of application
of growth regulators in relation to the number of flowers formed per plant was
statistically significant (Table 9). The highest number of
flowers was observed in T2 (55.49) and the lowest was in T1
(52.48). T3 produced the intermediate number of flowers per plant
(54.30). Table 10 showed that there was no significant difference
on number of flowers per plant within the treatments although the growth regulators
had positive effect over the control. 100 ppm GA3 produced the maximum
number of flowers (55.65) followed by 200 ppm GA3 (55.38) and the
control had the lowest (52.44). Interaction effect of different levels of growth
regulators and their time of spray showed significant variations on number of
flowers per plant (Table 11). The highest number of flowers
(63.33) was produced by T2C3 followed by T2C4
(60.33). The interaction of T1C0 had the lowest number
of flowers per plant (46.16).
| Fig. 3: | Effect of time of spray of growth regulators on number of branches per plant of soybean at different days after sowing.**, significant at 1% level |
Similar increase of flower number per plant due to the application of 100 ppm of GA3 was reported earlier in groundnut[13] and onion[20].
Number of pods per plant: Different times of application of growth regulators differed significantly in their inherent characters to produce pod per plant (Table 9). The highest number of pods (48.16) was observed in T2 while the lowest (39.24) was in T1. Growth regulators had highly significant effect on the number of pods per plant. Both concentrations of GA3 and lower concentration of MH significantly increased the number of pods over the control (Table 10). The highest number of pods (44.38) was recorded with 100 ppm of GA3 followed by 200 ppm GA3 (43.16) while the control plants had the lowest (35.09). Growth regulators in combination with different times of application showed significant variations on number of pods per plant (Table 11). The highest number of pods per plant (49.33) was obtained by T2C3 followed by T2C4 (48.16) and the lowest (29.62) was observed in the interaction of T1C0.
| Fig. 4: | Effect of plant growth regulators on number of branches per plant of soybean at different days after sowing.**, significant at 1% level |
In present experiment, 100 ppm GA3 significantly increased the number of pods per plant. Similar increase in the number of pods has been reported in groundnut[13] and chickpea[21] by the application of 100 ppm of GA3.
Number of seeds per pod: Different times of application failed to exert a significant influence on the number of seeds per pod. However, T2 had the superiority over T3 followed by T1 (Table 9). Growth regulators exerted highly varied influence on the number of seeds per pod (Table 10). All growth regulators were statistically similar in effect. However, 100 ppm of GA3 produced the highest number of seeds (2.19) and the lowest (1.86) was produced by the control. The interaction effect between different times of application and concentrations of growth regulators were found to be statistically significant (Table 11). The highest number of seeds (2.35) was obtained by T2C3 followed by T2C4 (2.32) and the lowest (1.77) was in T1C0.
In the present study, both GA3 and MH produced higher number of seeds per pod compared to the control. These results are in consistence with the findings of Abdel et al.[22] who noted that number of seeds per pod was increased in flax by 10-5 M GA3.
Seed yield per plant: Different times of application varied differently to produce seed yield per plant (Table 9). The highest seed yield (7.92 g) was obtained by T2 while the lowest (6.60 g) was observed in T1 which was statistically similar to T3 (6.69 g). Growth regulators exerted highly varied influence on seed yield per plant (Table 10). The highest seed yield (7.88 g) was produced by 100 ppm GA3 that is statistically similar to 200 ppm GA3 (7.59 g) and 100 ppm MH (7.45 g) and the lowest (5.68 g) was in the control. The data indicated that the lower concentrations of GA3 and MH were more effective than their higher concentrations. The results of the interaction effect of spraying time and different concentration of growth regulators were found statistically significant (Table 11). The highest seed yield (9.49 g) was obtained by T2C3 followed by T2C4 and the lowest (4.3 g) was in the interaction of T1C0.
Present study clearly shows that GA3 (100 ppm) has the potentiality to increase the seed yield per plant in soybean. Application of 100 ppm GA3 increased seed yield in rice[12,23], okra[11] and tomato[23]. In present experiment, the increase in seed yield might be attributed to the superior values of morphological (viz., plant height, leaf area, number of leaves and branches per plant) and yield contributing characters (viz., number of flowers and pods per plant and the number of seeds per pod) in plants treated with growth regulators.
Hundred seed (100-seed) weight: Hundred seed weight varied significantly with different time of application of growth regulators (Table 9). The highest 100-seed weight (15.86 g) was obtained in T2 while the lowest (14.68 g) was in T1 which is statistically similar to T3 (15.01 g). Application of growth regulators significantly influenced the 100-seed weight in soybean (Table 10). Among the concentrations of GA3 and MH, the significantly highest 100-seed weight (15.92 g) was found with 100 ppm GA3. Though the control produced the lowest 100-seed weight (14.68 g), the effect was statistically similar to the other treatments. Interaction effect showed that the highest 100-seed weight (17.59 g) was obtained by T2C3 followed by T2C4 (16.04 g) and the lowest (13.69 g) was observed by the interaction of T1C0 (Table 11).
Application of 100 ppm GA3 was reported to increase 100-seed weight in groundnut[13]. This result is inconsistence with the findings of our present experiment.
Seed yield (t ha-1): Average seed yield differed significantly with the time of spray (Table 9). The highest seed yield (2.16 t ha-1) was obtained by T3 and the lowest (1.93 t ha-1) by T1. Both GA3 and MH significantly increased seed yield over the control (Table 10). The highest seed yield (2.25 t ha-1) was obtained by 100 ppm GA3 followed by 200 ppm GA3 and the lowest (1.68 t ha-1) was in the control. It is clear from this study that GA3 has more promotive effect on seed yield than MH. Lower concentration of MH was more effective than its higher concentration. The result of the interaction of different concentrations of growth regulators and their time of spray on seed yield was found statistically significant (Table 11). The highest seed yield (2.59 t ha-1) was obtained by T2C3 and the lowest (1.46 t ha-1) was in the interaction of T1C0.
GA3 increased seed yield of soybean in this experiment. GA3-induced increase in seed yield have been reported in rice[12,23], soybean[6,7], bell pepper[22] and onion[25].
In conclusion, experimental results mentioned above revealed that both GA3 and MH brought about an improvement in morphological and yield contributing characters of soybean. Late spray (T3) of both regulators had better performance over the control and early spray (T1). However, interaction effect indicated that 100 ppm GA3 treated plants sprayed at 30 DAS (T2C3) showed the best performance. Further investigation may be undertaken with lower concentrations than 100 ppm and concentrations between 100 and 200 ppm which may contribute better effect in changes the morphological and yield contributing characters of soybean.