Tolerance differences among small seed soybean cultivars against excessive water stress conditions

Objectives of this study are to determine tolerance variability of small seed soybean cultivars against the excessive water stress (EWS) at V4 to V5 stage, and to provide the basic data to the parental selection for breeding. This experiment carried out on a concrete bed filled up with silt loam soil in greenhouse using 22 small seed soybean cultivars. The seed yield of 22 soybean cultivars treated with EWS for 10 days at V4 to V5 stage ranged from 42 g m ^-2 to 179 g m^-2. Sowonkong was the greatest yield 179 g m^-2, and Pureunkong and Sorogkong were the lowest yield 42 g m ^-2. The mean pod numbers of 22 soybean cultivars treated with non-EWS and EWS were 58.6 and 37.1 per plant, respectively. The number of seed of soybeans treated with EWS also decreased about 49% of that with non-EWS. The correlation coefficient was slightly higher in 20 days (r = 0.459, p < 0.05) after the removal of excessive water stress (REWS) treatment than in 10 days (r = 0.428, p < 0.05) after REWS. Also, the relationship between the relative seed yield and the relative number of pods per plant was positive correlation (r = 0.542, p < 0.01) under EWS for 10 days. On the other hand, the relationship between the relative seed yield and the number of seeds per plant was high positive correlation (r = 0.945, p < 0.001) under EWS for 10 days. These results with 22 small seed soybean cultivars indicated significant differences among cultivars for biomass, yield, and yield components. Sowonkong could be thought to be highest possibilities as a cultivar of excessive productivity under EWS conditions. Also, the above data suggest that the variability for flooding tolerance exists among small seed soybean cultivars and could be improved through repeating selection under EWS for 10 days at vegetative stage.