Genetic Diversity of Rhizobium Leguminosarum and Mesorhizobium Ciceri From Pea and Chickpea Fields in the Palouse.

Rhizobia bacteria, which fix atmospheric N in the nodules of legume roots, are important members of the soil microbial community of legume-cereal grain cropping systems. An improved understanding of genetic diversity among isolates of Rhizobia will facilitate the identification of strains with greater capacity to fix atmospheric N and improve the understanding of plant-microbe interactions. The objectives of this research were to isolate indigenous Rhizobium leguminosarum and Mesorhizobium ciceri from pea (Pisum sativum L.) and chickpea (Cicer arietinum L.) in the Palouse region of Washington and Idaho and to examine genetic diversity among these isolates and several commercial isolates. A total of 36 M. ciceri isolates were collected from four chickpea fields and 95 R. leguminsarum isolates were collected from five pea fields. Genetic relationships were determined based on DNA sequence analysis across several loci, including 16S rRNA,  nodC,  nifH and recA. Consensus trees based on R. leguminosarum nodC and nifH genes produced distinct clusters with bootstrap support values exceeding 60%, while those for recA and 16S rRNA genes were less discriminatory.  Nearly half of native R. leguminosarum isolates were clustered into a single large clade. A consensus tree based on the M. ciceri recA gene produced distinct clusters with robust bootstrap support values, while trees based on nifH, nodC, and 16S rRNA genes were less discriminatory. Commercial isolates of both species tended to group into clades that were distinct from clades containing the majority of indigenous isolates. Efforts are continuing to sequence other loci, including atpD and glutamate synthetase (GS), to further examine genetic diversity in this collection.