Genetic diversity and nitrogen fixation of mesorhizobia symbionts of New Zealand endemic Sophora species

Abstract

Forty-four rhizobial isolates from New Zealand endemic Sophora species growing in natural conditions were characterised and the effectiveness of selected isolates with regard to growth and N₂ fixation of different Sophora species was tested. Sequences for the housekeeping genes (concatenated recA, gln11 and rpoB) of the isolates were diverse but sequences for their symbiosis genes (nifH and nodC) were similar. Generally, isolates from the same field site showed similar housekeeping gene sequences. All isolates were Mesorhizobium. Twenty-six of the isolates aligned with Mesorhizobium species previously isolated from New Zealand native Sophora on the basis of their housekeeping gene sequences, but 18 isolates separated into two groups and a pair of isolates clearly separated from all Mesorhizobium type strains. DNA–DNA hybridisations indicated that isolates in the two groups could belong to two novel Mesorhizobium species. Rhizobial isolates with different housekeeping gene sequences (but similar symbiosis gene sequences) gave similar increases in dry weight and total N content of four Sophora species under glasshouse conditions.