CORRELATION OF PHYSIOLOGICAL CHARACTERISTICS WITH NODULATING ABILITY IN RHIZOBIUM JAPONICUM

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Abstract
A nodulating soybean strain and a mutant, non-nodulating sister soybean strain, and several strains of Rhizobium japonicum differing in nodulation response on these two plant hosts, were used to study specific biochemical requirements of the nodulation process. Screening of the bacterial strains revealed five physiological properties which correlated with ability or inability to nodulate the mutant soybean. High measurable indoleacetic acid formation, low indoleacetic acid destruction, high capsule formation, failure to metabolize nitrite, and failure to reduce triphenyl tetrazolium chloride were properties associated with ability to nodulate both normal and mutant soybeans. These same properties, opposite in magnitude, were associated with ability to nodulate only the normal soybean. These correlations were tested further by screening additional Rhizobium strains for the same properties. On the basis of the results obtained, nodulation response of the new strains on the mutant soybean was predicted. Only three of the five properties, namely low capsule formation, ability to metabolize nitrite, and ability to reduce triphenyl tetrazolium chloride, were present in all of the new strains. On the basis of these results it was predicted that these strains would not nodulate the mutant soybean. In subsequent nodulation tests, all strains failed to nodulate the mutant soybean. It was concluded from these experiments that high capsule formation, inability to metabolize nitrite, and failure to reduce triphenyl tetrazolium chloride are associated with the increased effectiveness of the rhizobial strains which nodulate both normal and mutant soybeans.