rass pea (Lathyrus sativus L.), belongs to the family Leguminosae, and is the only species widely cultivated as a food crop in the genus Lathyrus. A strong and penetrating root system allows grass pea to grow in a wide range of soil types including very poor soils and heavy clays, while its ability to utilize remnant water and soil nutrients makes the species adapted to low or zero inputs. In addition, it effectively nodulates with Rhizobium leguminosarum, leaving the soil enriched in nitrogen for the following crop. The main objectives of this work included the isolation of rhizobia that nodulate grass pea in different areas of Hamedan and East Azarbayjan provinces of Iran and characterization of the phenotypic and genotypic variability of native rhizobial populations. Rhizobial isolates were obtained from root nodules of L. sativus collected at different locations in two provinces of Iran. The nodulation ability of isolates was tested by inoculation of the host plant. Forty five phenotypic features were used for characterization of isolates. The modified YMA (yeast mannitol agr) medium was used to analyse the ability of isolates to use carbohydrates (1% glucose, adonitol, trehalose, galactose, arabitol, raffinose, lactose, fructose, sucrose, cellobiose and mannose) and amino acids (0.1% Lalanine, L-arginine, L-tyrosine, L-leucine and L-proline) as a sole carbon and nitrogen sources, respectively. Data from all the biochemical and physiological tests were coded using a binary system (1 for positive and 0 for negative). A matrix was generated by numerical analysis and the dendrogram was constructed by the unweighted pair group method with average (UPGMA) clustering method. For genotypic analysis, from 33 strains, fifteen isolates chosen as representatives for patterns of each 16S rDNA, housekeeping genes of atpD, recA and symbiotic genes of nodC and nifH. The results of the genes sequences were analysed for homologies to sequences deposited in the GenBank. The deter
