Author : Parinya Sebunruang; Lantican, Ricardo M.

Summary : Two sets of graft experiment in soybeans were conducted to determine the individual effects of the long juvenile trait from tropical varieties and the supernodulating characteristics from a Bragg mutant and the joint effect on plants if the two traits were combined in one plant through grafting. Experiment 1, under long-day conditions, showed that grafting tropical varieties onto NTS382, the supernodulating mutant, resulted in delayed flowering (by 2 to 16 days) and maturity and increased vegetative dry weight and seed yield. However, the same graft treatment on NTS382 reduced the number of nodules, but N2-fixation efficiency remained high. Experiment 2, under short-day conditions, showed relatively shorter lengths of vegetative and reproductive period and early maturity. This resulted in lower dry matter accumulation, reduced nodulation and N2-fixation efficiency, and less grain yield. However, vegetative dry weight and seed yield of NTS382 was significantly increased when tropical varieties were grafted unto it due to a prolongation of the vegetative period. This overcame the limitations imposed by short day length, and increased biological nitrogen fixation. Actual hybridization involving the supernodulating mutant, NTS382, and the long juvenile gene sources such as IPBSy91 and UPSy10 may result in genotypes with combined high nodulation, high N2-fixation efficiency, ideal phenological development, and high seed yield under tropical environments.