Symbiotic properties of hypermotile mutants of Bradyrhizobium sp. (Vigna aconitifolia)

An attempt was made to isolate hypermotile mutants of cowpea Rhizobium MR125s 2 -sm r 8 through UV mutagenesis. A "capillary movement" step was involved to trap hypermotile individuals from the mutagenised populations. In one case entrapped cells formed larger swarm as compared to the parent. This swarm was subjected to 3 cycles of peripheral cell enrichment and from that 50 individual isolates were tested both for swarm size and nodulation. Majority of the isolates (74%) showed large stable swarm when compared to the parent. The nodulation was, however, considerably affected. Twenty six isolates lost nodulation ability. The mutants, whose swarm size was larger and produced pinkinsh nodules, were further characterized. On culture medium the parent and mutants preferred KNOB as sole N source over yeast extract and did not grow on media containg glucose or maltose. On the basis of N content in plant, the mutants varied significantly from each other. When coinoculated with the parent, mutant had generally higher nodule occupancy.