Symbiotic characteristics of Rhizobium meliloti from the brown acid soils of the Macquarie region of New South Wales.

Abstract

Thirty-three isolates of Rhizobim meliloti were obtained from the brown acid soils of the Macquarie region of New South Wales and their symbiotic behaviour in association with 11 species of Merlicago and three species of Melilotus was investigated in the laboratory. In respect of nodule formation, there were two distinct types of Rhizobiurn and the hosts formed three groups. In respect of nitrogen fixation there were six strain types and seven host, groupings. These host and bacterial groups could be arranged in a series. Several of the strains of rhizobia, and one in particular, were found to fix a high level of nitrogen with a number of hosts, but, except for ;Medicago denticulata Willd. and Melilotus indica (L.) All. which behaved identically in all features of the symbiosis studied, no definit'e groupings on this criterion were apparent in either hosts or bacteria. The possible application of the results to the selection of strains of' Rhizobium meliloti suitable for seed inoculation is discussed.