Influence of Soil and Nonsoil Environments on Nodulation by Rhizobium trifolii

Indigenous serotypes 1-01 and 2-02 of Rhizobium trifolii occupied similar percentages (18 to 23%) of root nodules on soil-grown subclover (Trifolium subterraneum L.) and were virtually absent (4.5%) from nodules of soil-grown white clover (Trifolium repens L.). In contrast (with the exception of one dilution [10]), serotype 1-01 occupied a substantial portion of nodules (16 to 40%) on white clover seedlings grown on mineral salts agar and exposed to samples of the same soil in the form of a 10-fold dilution series (10 to 10). Under the latter conditions, occupancy of subclover nodules by 1-01 and of nodules of both plant species by 2-02 was consistent with the results obtained with soil-grown plants.