Author : Musliar Kasim

Summary : Two screenhouse experiments and a field experiment was conducted at the University of the Philippines Los Ba¤os (UPLB) from October 1990 to May 1991. The objective was to determine the influence of different abscisic acid (ABA) concentrations (0, 10 (superscirpt -5) and 10 (superscript -4) M) and times of application (vegetative stage and reproductive stage) on the growth, grain yield, and seed quality of two soybean cultivars (BPI-Sy4 and SJ-2) grown screenhouse conditions (30 percent and 100 percent available water to simulate drought and sufficient water conditions, respectively) and field conditions (irrigated and unirrigated). Grain yield of two cultivars either grown under either drought sufficient water condition were not significantly affected by ABA and its time of application. However, plant maturity was significantly longer when applied with ABA than when untreated, especially those grown condition. Both soybean cultivars had significantly higher yields than when under drought condition. Grain yield of SJ-2 was significantly higher than that of BPI-Sy4 under sufficient water conditions. No significant yield difference, however, was observed under drought condition. ABA application significantly reduced the dry matter, leaf area, and root dry weight of the two cultivars grown in the screenhouse. Compared with the untreated control, these reductions were greater at 10 (superscript -5)M ABA than at 10 (superscript -4)M ABA under sufficient water conditions. Under drought conditions, however, the reverse was observed. Reduction in these parameters were also greater when ABA was applied at the vegetative stage than at the reproductive stage. The two cultivars responded differently to ABA application in terms of stomatal conductance, dry matter, shoot dry weight, number of pods, and maturity. Generally, there were less reduction in these parameters in BPI-Sy4 than in SJ-2, although growth of SJ-2 cultivar was better than BPI-Sy4. On the other hand, ABA application had no significant effect.