PHYSIOLOGICAL VARIATIONS AND HOST PLANT SPECIFICITIES OF RHIZOBIA ISOLATED FROM CARAGANA ARBORESCENS L.

Abstract

The physiological characteristics and host plant relationships of 14 strains of rhizobia, isolated from the nodules of Caragana arborescens L., have been studied. The nodules from which these isolates were obtained came from six widely separated localities in North America. The strains differed markedly in rates of growth, in their ability to reduce nitrate, in their reactions in litmus milk and on 12 carbohydrate media, and in their abilities to fix nitrogen symbiotically. The strains showed uniformity in their abilities to produce nodules on Phaseolus vulgaris, Colutea arborescens, Lespedeza stipulacea, Trifolium pratense, and Lotus corniculatus. Because these species are now included in separate bacterial–plant groups, an assignment of C. arborescens to a cross-inoculation group appears unwise at this time. Thirty strains of rhizobia isolated from 20 species contained in 15 leguminous genera failed to nodulate C. arborescens in greenhouse tests. Various examples of nonreciprocal cross-inoculation were noted. Strains of caragana rhizobia reisolated from nodules formed by them on Trifolium pratense and Colutea arborescens retained their abilities to form nodules on Caragana arborescens.