Effect of Bioregulators on Growth , Yield and Chemical Constituents of Soybean ( Glycine max )

A three-year study was conducted during 2006-2008 in India (Manipur) to study the response of soybean variety JS 335 to salicylic acid @ 50 ppm, Ethrel @ 200 ppm, Cycocel @ 500 ppm and control (water spray) applied as foliar spray at different stages viz. flower-initiation (40 DAS), pod-initiation (60 DAS) and flower-initiation + pod-initiation. The study revealed that application of Ethrel @ 200 ppm at both flower-initiation (40 DAS) + pod-initiation (60 DAS) gave higher vegetative growth, yield, net returns and B:C ratio as compare to salicylic acid @ 50 ppm, Cycocel @ 500 ppm and control. However, maximum chlorophyll content and carotenoids were obtained from cycocel @ 500 ppm treated plants.


Introduction
Plant growth regulators are known to enhance the source-sink relationship and stimulate the translocation of photo-assimilates thereby helping in effective flower formation, fruit and seed development and ultimately enhance productivity of the crops.Growth regulators can improve the physiological efficiency including photosynthetic ability and can enhance the effective partitioning of accumulates from source and sink in the field crops (Solaimalaiet al., 2001).Salicylic acid (C 7 H 6 O 3 ) is an endogenous growth regulator of phenolic nature, which participates in the regulation of physiological processes in plant, such as stomatal closure, ion uptake, inhibition of ethylene biosynthesis, transpiration and stress tolerance (Khan et al., 2003 andShakiroveet al., 2003).Foliar application of salicylic acid exerted a significant effect on plant growth metabolism when applied at physiological concentration and thus acted as one of the plant growth regulating substances (Kalaraniet al., 2002).Salicylic acid increased the number of flowers, pods/plant and seed yield of soybean (Gutierrez-Coronado et al., 1998); enhanced wheat growth (Shakirovaet al., 2003) and maize growth (Shehetaet al., 2001;Abdel-Wahedet al., 2006;El-Mergawi and Abdel-Wahed, 2007).
Ethylene released from ethrel (2-Chloroethylphosphonic acid) could possibly be utilized for promoting pod growth as Abbas (1991) has shown that early pod development is related to higher ethylene levels, thus decreasing flower and pod shedding and thereby reducing abscission and improving better pod set.Ethrel induced increase in cell division, resulting in increased fruit size and yield have been reported in tomato fruits (Atta -Alyet al., 1999).In cucurbits ethrel application at 250 ppm promoted pistillat flower formation (Robinson et al. 1970).
Cycocel (2-Chloroethyl, trimethyl ammonium chloride) has been used to check the abscission of flower and modify the crop canopy for improving the yield in gram (Bangalet al., 1982), pigeonpea (Vikhiet al., 1983) and soybean (Singh et al., 1987). Grewalet al., (1993) reported that cycocel improves the translocation of photosynthates.More protein content stored in the seeds might be due to improvement of translocation of photosynthates to the seeds.
Agricultural application of vegetal bio-regulators is becoming a useful practice that has improved the yield of beans, corn and soybean (Vieira and Castro, 2004).The aim of present work was to study the effect of the three bioregulators (Salicylic acid, Ethrel and Cycocel) and their stages of application on growth, yield and biochemical constituents of soybean.The soil was clay loam in texture with pH of 5.4.The treatments consisted of three bioregulators viz.Salicylic acid @ 50 ppm, Ethrel @ 200 ppm and Cycocel @ 500 ppm with three different stages of application (flower-initiation, pod-initiation and flower-initiation + pod-initiation).Control treatment was sprayed with distilled water at the same stages.The experiment was laid out in factorial randomized block design with three replications.Recommended dose of NPK for soybean 20 kg N, 60 kg P 2 O 5 and 40 kg K 2 O/ha was applied at the time of sowing through urea, single super phosphate and muriate of potash.The seeds were treated with Bavistin @ 2.5 g/kg seed before sowing.The plot area was 21.6 m 2 (6 x 3.6 m) and seeds of soybean cultivar JS 335 was sown on 8 th June, 10 th June and 8 th June 2006June , 2007June and 2008 respectively in rows 45 cm apart and 10 cm between plants.The crops were harvested on 12 th , 18 th and 15 th October 2006, 2007 and 2008 respectively.

Growth characteristics
Plant height and number of braches/plant were recorded at the time of maturity whereas dry weight/plant and leaf area index were recorded at 75 days after sowing.

Yield and its components characteristics
Yield and its components such as number of pods/plant, number of seeds/plant, seed index, grain yield, straw yield and harvest index were determined at maturity stage.

Chemical analysis
Grain samples were dried at 70 o C for constant weight and ground to determine the chemical constituents such as protein and oil percentage.The oil content of soybean seeds was estimated by adopting Soxhlet Ether Extraction method (Sadasivam and Manickam, 1996).Protein content was determined by the Kjeldahl method (total nitrogen), as recommended by the Association of Official Analytical Chemists (AOAC, 1975), with modifications.Nitrogen contents were multiplied by dry matter-based factor 6.25 to determined total protein content (Gupta &Varshaney, 1994).

Estimation of photosynthetic pigments
The blade of the third leaf from tip (terminal leaflet) was taken at 75 days after sowing to determine photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids) by the spectrophotometic method recommended by Metzneret al. (1965).Taking into consideration the dilution made, it was possible to determine the concentration of the pigment fraction (chlorophyll a, chlorophyll b and carotenoids) as ug/ml using the following equations: Where, E is equal optical density at the given wave length The average data of 3 years were subjected to statistical analysis in factorial randomized block designed as per method of Gomez and Gomez (1984).

Growth parameters
Data presented in Table 1 showed that foliar application of Salicylic acid @ 50 ppm and Ethrel @ 200 ppm significantly increased the plant height over Cycocel @ 500 ppm and control (Table 1).Cycocel is an anti-gibberellin dwarfing agent, and foliar spray of this may induce deficiency of gibberellins in the plant and reduce the growth by blocking and conversion of geranyl pyrophosphate to coponyl pyrophosphate which is the first step of gibberellins synthesis (Moore, 1980).Significantly higher number of branches, dry weight and leaf area index was observed with bioregulators over the control.Ravinchandran and Ramaswami (1991), also indicated that the application of mepiquat chloride, cycocel and TIBA significantly increase the amount of dry matter production in soybean.

Photosynthetic pigments
The data recorded in Table 2 showed that Photosynthetic pigments content were increased significantly with the application of bioregulators at flower-initiation + pod-initiation stages than the other stages.The increased chlorophyll content of Cycocel treated plants could be referred to hormonal effects as it has been noted earlier that ancymidol stimulate chlorophyll biosynthesis through acceleration of chloroplasts differentiation and stimulating photosynthetic enzymes (Chung Jaedonget al., 1999).The present results are in agreement with those obtained by many investigators (Bekheta 2004 andBekhetaet al., 2006).The effect of cycocel in increasing chlorophyll contents may be due to the reduction in cell size resulting in dense cytoplasm (Appleby et al., 1966).
The results are in conformity with early reports in soybean (Bora and Sarma, 2004).

Yield and its components
Data recorded in Table 3 and 4 showed that spraying of bioregulators caused a marked effect on number of pods per plant, seed yield, straw yield and harvest index in comparison to the untreated plants.Application of Ethrel @ 200 ppm gave significantly higher yield (1.75 t/ha) over the other treatments when applied at both flower-initiation and pod-initiation stages.Ethrel has been reported to improve productivity of pulse crops like cowpea, pigeonpea, mungbean and soybean by increasing the number of pods, seed weight and seed yield (Chandra 1985, Bora andBahra 1989).Beneficial effect of Ethrel on increased flowering, fruit size and fruit yield have also been reported in tomato (Atta-alyet al., 1999).Ethylene released from Ethrel could possibly be utilized for promoting pod growth as Abbas (1991) has shown that early development is related to higher ethylene levels, thus decreasing flowering and pod shedding and thereby reducing abscission and improving better pod set.Harvest index was increased due to spraying the plants with bioregulators as compared to control.The increase in the yield recorded in this investigation could be a reflection of the effect of bioregulators on growth and development, it might be due to (a) marked increase in the number of branches per plant (Table 1) which gave a chance to the plant to carry more flowers, pods and hence more seeds (b) marked increase in the photosynthetic pigments content (Table 2), which could lead to increase in photosynthesis, resulting in greater transfer of assimilates to the seeds and causing increase in their weight (Table 3).

Oil and Protein content
Growth regulators also caused an increase on oil and protein content in the seeds (Table 5).Grewaletal., (1993) reported that cycocel improves the translocation of photosynthates.More protein content stored in the seeds might be due to improvement of translocation of photosynthates to the seeds.Afriaet al. (1998) reported that cycocel resulted in a significant increase in protein content in wheat.

Conclusion
From the above findings it can be concluded that application of Ethrel @ 200 ppm as foliar spray at flower-initiation (40 days after sowing) + pod-initiation (65 days after sowing) stages gave higher vegetative growth, yield, net returns and B:C ratio as compare to Salicylic acid @ 50 ppm , Cycocel @ 500 ppm and control.
Table 1.Effect of bioregulators on vegetative growth parameters of soybean (average for three years) wereconducted for 3 consecutive years at the Agricultural Research Station of Central Agricultural University, Imphal during 2006-2008 under All India Coordinated Research Project on Soybean.

Table 2 .
Effect of bioregulators on photosynthetic pigments of soybean (average for three years)

Table 3 .
Effect of bioregulators on yield components of soybean (average for three years)

Table 4 .
Effect of bioregulators on yield of soybean (average for three years)

Table 5 .
Effect of bioregulators on oil and protein content of soybean seed (average for three years)