Compatibilidade de fungicida via semente e fixação simbiótica em feijoeiro-comum

Abstract

Seed treatment with fungicide is an important strategy for controlling the main pathogens of the common bean culture. However, there are reports concerning its damage to biological nitrogen fixation (BNF). The aim of the study was to determine whether seed treatment with fungicides interferes with the symbiotic effectiveness of the CIAT 899T strain, inoculated via seed and sowing groove, as well as the quality of treated seeds. Three field experiments were conducted: in Lavras, dry/2014 crop in a randomized blocks statistical design with three replicates and a (5x3) + 1 factorial scheme, and in Lavras and Lambari, winter/2014 crop in a randomized blocks design with three replicates and a 6x4 factorial scheme. The fungicides treatments were: 1. Captan, 2. Carboxin + thiram 3. Difenoconazole, 4. Fluazinam + thiophanate-methyl and 5. Fludioxonil + metalaxyl-M, and the first experiment, additional treatment was witness, with no fungicide. In the other experiments, the witness was part of the factor. At first, we used three inoculation levels of CIAT 899T Rhizobium tropici strain (no inoculation, inoculation via seeds and inoculated via groove). Subsequently, we added another level of inoculation (no inoculation, fertilized with 80 kg ha-1 N). Each experimental plot had six lines of 4 m, spaced in 0.60 m, with BRS MG Madrepérola. Laboratory tests were also conducted to determine the physiological and sanitary quality of the seeds used, assessing the survival of strains in direct contact with the fungicides. We concluded that seed treatments with fungicide do not interfere in nodulation, growth and yield of bean grains, also not affecting germination and seed emergence. The Difenoconazole and Captan fungicides promoted high in vitro mortality of inoculated bacteria (strain CIAT 899T ) in seeds. The Carboxin + thiran and Fluazinam + thiophanate methyl fungicides showed decreased seed vigor. Fertilization with 40 kg ha-1 of nitrogen at sowing decreased nodulation and plant stands, but promotes higher nitrogen content and accumulation in plants and grains. The native soil bacteria shows equivalent efficiency to the CIAT 899T strain inoculated via groove and via seed in terms of nodulation, growth, nitrogen nutrition and grain yield. The environment has great influence over nodulation, nitrogen content and accumulation, the grain yield and over occurrence of bean diseases.