Anthracnose has become one of the main threats to soybean production and is considered the most important disease in some soybean-producing areas. Colletotrichum truncatum is the species most commonly associated with anthracnose and produces microsclerotia. However, the role of microsclerotia in the epidemiology of soybean anthracnose disease has not yet been described. The aim of this study was to determine whether C. truncatum microsclerotia can survive and maintain pathogenicity for a period of up to 246 days, corresponding to the off-season period of soybean cultivation in Brazil. Therefore, microsclerotia of two pathogenic isolates of C. truncatum (CMES1059 and LFN0297) were produced and placed in polyester bags, which were kept under field conditions either on the soil surface under maize straw or buried 8-cm deep. The bags were collected monthly for a period of up to 246 days to assess the viability of microsclerotia based on their germination and typical colony growth. The logistic regression model was used for data analysis considering viable and nonviable microsclerotia. In addition, periodic sowing of soybean was done in the soil infested with LFN0297 microsclerotia to test pathogenicity up to 246 days after soil infestation. C. truncatum microsclerotia survived from 92 to 246 days in the field soil, with the highest recovery of viable microsclerotia at 153 days. C. truncatum was reisolated from soybean plants sown in infested soil at 245 days postinoculation. The isolates from the last microsclerotia sampling from the field (246 days) and those obtained from a plant at the last sowing date (245 days) had the same genotypic profile for 12 microsatellite loci as the isolates used to perform the experiments. C. truncatum microsclerotia in soil may serve as the primary inoculum for soybean anthracnose.
Keywords: Brazil; Glycine max; primary inoculum; soybean anthracnose; survival structure.