Seleção de isolados e métodos de inoculação de Macrophomina phaseolina em soja

Abstract

Soybean gray root rot, caused by the fungus Macrophomina phaseolina, is widespread in crops in Brazil, especially in areas where there is a deficit, causing losses in productivity, quality, and profitability due to deterioration of seeds, roots, and plant collars. In this context, the objectives of this study were: to evaluate the aggressiveness of ten M. phaseolina isolates from different Brazilian states on the cultivars Brasmax Bônus IPRO and Brasmax Desafio R; and to evaluate four inoculation methods: infestation of the seeds in contact with the pathogen for 12, 24 and 48 hours, infestation of the substrate, immersion in mineral oil and “straw-test” and select the best method for the development of the infectious process; and classify three cultivars and two genotypes of soybean, according to the level of resistance to M. phaseolina. All the experiments were conducted in a greenhouse with controlled temperature and irrigation. The results obtained were presented in the form of two chapters. In the first chapter, it was shown that all the isolates were pathogenic to both soybean cultivars and presented variability in terms of aggressiveness. In the second chapter, the seed infestation method with exposure time to the pathogen for 48 hours was the most effective in reproducing the symptoms of the disease and based on the percentage of relative emergence of the seeds, the cultivars Brasmax Origem IPRO, Brasmax Tormenta CE, Brasmax Olimpo IPRO and the genotype B75C92 were classified as susceptible and the genotype BG4786 as moderately susceptible, when exposed to the aggressive isolate of the pathogen MACRO - UFU 2, for 48 hours. This work contributes to the protection of the soybean production chain in Brazil by indicating a reference isolate of the pathogen and an efficient inoculation method for screening and selecting soybean genotypes resistant to M. phaseolina.