Studies on Induced Variation in the Rhizobia

The rhizobial bacteria can be readily grown on a variety of media containing complex nutrient extracts of microbial, mineral, or plant origin, but growth on nonsupplemented carbohydrate-inorganic salts media is poor for most species. Only a minor part of the extensive research devoted to Rhizobium has dealt with the minimum requirements for cultural growth (Wilson, 1940; Wilson and Wilson, 1942; Allen and Allen, 1950). Establishment of minimal media is prerequisite to the isolation of nutritional mutants, potentially useful in the study of the biochemical basis of nodulation (infectiveness) and nitrogen fixation (effectiveness). Besides establishing a need for media adapted to specific cultural experiments, the induction of such cultural marker characters requires periodic testing of variants for retention of infectiveness and effective-