Application of abscisic acid promotes yield in field-cultured soybean by enhancing production of carbohydrates and their allocation in seed

This study investigates the effect of abscisic acid (ABA) and gibberellin (GA(3)) applications on physiological and productive parameters in complementary experiments performed with soybean cultured in the field for 3 crop seasons and in the greenhouse for 1 crop season. ABA300 mg/L was sprayed at the V7 and R2 phenological stages, while GA(3) 300 mg/L was sprayed at R2 and repeated 7 days later. GA(3)-treated plants had longer shoots and ABA-treated plants had greater dry weight of aerial parts. Nodule formation was not affected, but both shoot diameter and root density were greater in ABA-treated plants. ABA increased leaf area and chlorophyll content, while GA(3) diminished them. In ABA-treated plants, there was a significant reduction in leaf conductance 24 h after the hormone had been applied, but then the conductance values started to rise and equalled those of the controls 11 days later. Although there were no differences in number of pods, in GA(3)-treated plants the number of seeds per pod was lower, and in ABA-treated plants, young pods were bigger. ABA application increased soybean yield by enhancing carbon allocation and partitioning to the seed. Exogenous ABA also improved the seed quality since it did not affect protein levels but enhanced oil concentration, while GA(3) spraying increased oil concentration but diminished seed proteins.