On the resistance of effectiveness ofRhizobium trifolii to a low pH

Abstract

ThreeRhizobium trifolii strains were subcultured repeatedly on agar medium of pH values ranging from 3.5 to 7.0. Growth was retarded at pH 4.5 and very poor at pH 4.0 and 3.5, although the cells were not killed at the lowest pH. After 12 subcultures during a period of 300 days on these media, the symbiotic effectiveness was estimated by inoculating aseptic seedlings of white clover in test tubes containing Jensen's agar medium at pH 6.5. The number of nodules formed on the plants and the effectiveness of some strains seemed to be affected by growing the rhizobium for a long period at a low pH. All test plants produced nodules with red pigment.