Seed treatment with fungicides does not affect symbiosis between common bean and rhizobia

Abstract

Results of the few studies on the symbiosis of rhizobia and common bean (Phaseolus vulgaris L.) that have evaluated the effects of new fungicides applied to seeds have been inconclusive, that is, some showed no effects and others showed harmful effects. This study tested the compatibility between commercial fungicides, currently recommended for treatment of seeds, and symbiosis of common bean with rhizobia. Two field experiments were performed in the 2012/2013 spring–summer crop season in two Brazilian municipalities. A randomized block experimental design with four replicates and a 5 × 2 factorial arrangement was used, consisting of five seed treatments {the fungicides: carboxin(carboxamide) + thiram (dimethyldithiocarbamate) = Vitavax-Thiram (Macdermid Agricultural Solutions Ltda, Sumaré, Brazil); fludioxonil(phenylpyrrol) + metalaxyl-M(acilalaninato) = MaximXL (Syngenta Ltda, São Paulo, Brazil); fluazinam (phenylpyridin-amine) + thiophanate-methyl[benzimidazole(precursor of)] = Certeza (Iharabras S.A., Sorocaba, Brazil), and carbendazim (benzimidazole) = Carbomax (Nufarm S.A., Maracanaú, Brazil) and one control without fungicide} with or without rhizobial inoculation. Seeds from the cultivar BRSMG Madrepérola were treated with the fungicides at manufacturer recommended application rates and then inoculated with Rhizobium tropici strain CIAT899T. The majority of parameters related to nodulation, plant growth, and N nutrition showed significant differences between sites. However, all parameters had values within or above the acceptable ranges. Depending on the site, the fungicide carboxin+thiram decreased the stand of plants, and carbendazim resulted in lower grain N concentration. However, regardless of the site, the fungicides did not influence nodulation, plant growth, shoot N concentration, or grain yield at the application rate recommended by the manufacturers.