COMPARISON OF SYMBIOTIC EFFECTIVENESS OF RHIZOBIUM SP WITH POSITIVE HYDROGEN-UPTAKE ACTIVITY COMPARED WITH NEGATIVE MUTANTS IN RELATION TO NITROGEN-FIXATION IN MUNGBEAN (VIGNA-RADIATA L)

H-2 uptake activity was well distributed in Rhizobium sp. strains isol ated from nodules of mungbean (Vigna radiata L.). Two effective strain s, RMP1 und RMP2, exhibiting significantly higher H-2 uptake activity were subjected to mutagenesis with nitrosoguanidine. The respective mu tation frequencies were 0.18 and 0.19%. Three Hup(-) mutants each of R MP1 und RMP2 were compared with the wild-type parent strains under pot culture experiments to evaluate the significance of the H-2 uptake sy stem in biological N-2 fixation. Nodulation capabilities, plant growth characteristics, and the chlorophyll content of the leaves were signi ficantly reduced in the plants treated with Hup(-) mutants. Nitrogenas e activity in Hup(-) nodules was reduced by 8-41%. Similarly, N accumu lation was also reduced significantly.