The preference for strains of Rhizobium meliloti by cultivars of Medicago sativa grown on agar

Abstract

Variation in nodulation preference within and between cultivars of Medicago sativa for Rhizobium strains was assessed under axenic conditions using inocula consisting of paired strains of R. meliloti which could be recognized by distinctive colony morphology or antibiotic resistance. The largest variability in host preference for Rhizobium strains was among plants within cultivars and not between cultivars. The implications of such variation are discussed in the context of possible enhancement of symbiotic nitrogen fixation. An isolate of R. meliloti which had been marked with antibiotic resistance and cured of a cryptic plasmid was significantly less successful in nodulation than its wild-type parent strain in all inoculated combinations. The interaction of inoculum and cultivar on yield indicated differential symbiotic effectiveness of strains of R. meliloti on cultivars of M. sativa.