Symbiovar loti genes are widely spread among Cicer canariense mesorhizobia, resulting in symbiotically effective strains

Abstract

Cicer canariense has been shown to be a promiscuous legume. The symbiotic characteristics of several C. canariense mesorhizobial genospecies harbouring similar symbiotic genes are studied. Comparative analysis of nodA and nifH gene phylogenies, and characterization of the symbiotic phenotypes on the basis of nodulation and nitrogen fixation was performed. Phylogenetic analyses of the nodulation gene nodA was in complete agreement with those previously done on nodC in grouping these mesorhizobia within symbiovar loti. In the nifH phylogeny, however, these strains were resolved into two subgroups named nifH-1 and nifH-2. Subgroup nifH-1 contained strains from two genospecies and correlates with symbiovar loti, as it clustered with Mesorhizobium reference strains nodulating Lotus corniculatus. In contrast, subgroup nifH-2 contained strains of the other seven genospecies without reference strains and formed a distant branch on its own. Strains combining symbiovar loti genes in any chromosomal background effectively nodulated C. canariense, although with significant differences in nitrogen fixation capabilities. Symbiovar loti genes are the most widely spread in the mesorhizobia that nodulate C. canariense in its natural habitat. They included two variants of the nifH gene and were found to be associated with nine chromosomal backgrounds (genospecies), resulting in strains showing different symbiotic effectiveness. Mesorhizobium tamadayense symbiovar loti strains were the most effective in this legume.