Characterization of Rhizobia from Ineffective Alfalfa Nodules: Ability to Nodulate Bean Plants [ Phaseolus vulgaris (L.) Savi.]

Publisher Website
Google Scholar
Abstract
This study was initiated to characterize Rhizobium isolates obtained from root nodules of ineffectively nodulated, field grown alfalfa (Medicago sativa L.) plants. The purpose was to determine if these isolates possessed characteristics which would explain either their ineffectiveness in N2 fixation or their apparent ability to tolerate the moderately acid soil conditions from which they originated. Isolates were characterized by analysis of growth rate, 39.degree. C tolerance, acid production on conventional media, and symbiotic performance. All isolates were ineffective in N2 fixation on alfalfa, and they contained one or more anomalous characteristics. These included either slow growth rate, lack of 39.degree. C tolerance, or lack of acid production on conventional media. Infectiveness tests on a broad range of legumes revealed that the isolated formed root nodules on M. sativa, Medicago lupulina L., and Phaseolus vulgaris (L.) Savi. (common bean). These results provide evidence that, in some situations, ineffective nodulation of M. sativa in the field may be due to the presence of promiscuous, native Rhizobium species.