The fungicides thiram and captan affect the phenotypic characteristics of Rhizobium leguminosarum strain C1 as determined by FAME and Biolog analyses

We assessed the effects of the fungicides captan and thiram on the survival and phenotypic characteristics of Rhizobium leguminosarum by. viceae, stra in C1. Fungicide was applied to pea seed at rates of 0.25-2 g a.i. kg(-1) s eed, and treated seed was inoculated with strain C1. After 24 h, rhizobia w ere extracted from treated seed and viable numbers determined by plating on to yeast extract mannitol agar. Phenotypic characteristics were assessed us ing FAME (fatty acid methyl ester) profiles and Biolog substrate utilizatio n patterns. Captan and thiram significantly reduced the numbers of rhizobia recovered from seed and altered the FAME and Biolog profiles of recovered rhizobia. However, only the highest concentrations of captan affected nodul ation and plant growth. Contact with some seed-applied fungicides can signi ficantly alter phenotypic characteristics of rhizobia, but these changes mi ght be offset by the presence of host plants.