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, strain C1. Fungicide was applied to pea seed at rates of 0.25-2 g a.i. kg(-1) seed, and treated seed was inoculated with strain C1. After 24 h, rhizobia were extracted from treated seed and viable numbers determined by plating onto yeast extract mannitol agar. Phenotypic characteristics were assessed using FAME (fatty acid methyl ester) profiles and Biolog substrate utilization 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 nodulation and plant growth. Contact with some seed-applied fungicides can significantly alter phenotypic characteristics of rhizobia, but these changes might be offset by the presence of host plants.