Variation in the Nitrogen-fixing Property of Rhizobium trifolii

Abstract

WHILE testing a number of strains of Rhizobium trifolii, two cases have occurred (cultures 61 and 91, isolated from Trifolium tomentosum L. and Trifolium glomeratum L. respectively) in which a culture, from a single colony developed from a single nodule, has shown at the time of its first testing on white clover (T. repens L.) the presence of definite 'sub-strains' with distinctly different nitrogen-fixing ability. Culture 91 showed the same behaviour when tested against T. glomeratum. In each case, while some plants were scarcely better than those of the uninoculated control, other plants in the same pot were very much better. The former showed the usual characteristics associated with inefficiency, namely, early yellowing of cotyledons, poor yellow growth and the presence of many small nodules. The healthier plants carried typically large effective nodules, although other smaller nodules, similar to those on the poorly grown plants, also occurred.