Abstract

Rhizobial strains that nodulate Vigna radiata (mungbean) were examined for their resistance to several stress conditions. One strain of mungbean rhizobia was selected to construct a collection of transposon mutants based on resistance to high temperature (40°C), alkalinity (pH 8.0) and several heavy metals. One mutant that is deficient in resistance to high temperature, alkalinity and zinc was selected to estimate the relation between resistance to stress conditions and symbiotic performance. Southern hybridization analysis showed a single transposon insertion in the mutant strain. The impaired symbiotic performance was observed in the host plants inoculated with the mutant strain as compared with the wild-type strain. This result suggested that genes involved in stress resistance affected the symbiotic ability. The 16S rDNA sequence analysis revealed that the strain is a member of Bradyrhizobium with 98% identity.

Key words: Bradyrhizobium, mutant, transposon, stress tolerance, symbiosis.