Diversity within two serogroups ofRhizobium leguminosammnative to soils in the Palouse of eastern Washington*

SUMMARY The effect of plant genotype, soil temperature, and moisture on recovery ofRhizobium leguminosammserogroups WA01 and WA02 from soil, was evaluated in the greenhouse using three plant genotypes (Pisum sativumcv. Alaska,Pisum sativumcv. Paloma andLens culinariscv. Rechief), three temperatures (12, 20 and 24°C) and soil from two different slope positions. The impact of moisture was followed by assessing pea nodulation after incubation of soil at different preplanting moisture levels. Isolates were also evaluated for serogroup, response to low levels of antibiotics and efficacy of symbiotic characters. Of the 33 antibiotic‐strain combinations showing growth, 10 permitted 50% or more of the isolates to grow. Of the 24 clusters obtained, all except one were dominated by isolates in either serogroup. WA01 or WA02. There was no relation between either serogroup or cluster groupings and N2fixation. Serogroup recovery was influenced by plant genotype and temperature. At root temperatures of 12 and 24°C, serogroup WA02 occurred in a significantly lower fraction of the lentil nodules as compared to the pea species. At 12°C, recovery of WA02 was higher for the Paloma than Alaska pea. Recovery of WA02 in pea nodules generally increased as the soil moisture was preconditioned to drier levels of ‐0.5 and ‐1.5 MPa water potential.