Survival of Colletotrichum truncatum as Microsclerotia in Soil

Abstract

Anthracnose is becoming 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. The role of these structures in the epidemiology of soybean anthracnose disease has not yet been described. This study intended to determine if C. truncatum microsclerotia can survive and maintain pathogenicity for periods of up to 246 days, corresponding to the off-season period of soybean 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 periods of up to 246 days to assess the viability of microsclerotia using germination and typical colony growth. The logistic regression model was used for data analyses considering viable and non-viable microsclerotia. In addition, periodic sowings of soybean were made in soil infested with LFN0297 microsclerotia to test pathogenicity up to 246 days after soil infestation. Colletotrichum truncatum microsclerotia survived from 92 to 246 days in the field soil, with the highest recovery of viable microsclerotia at 153 days. Colletotrichum truncatum was reisolated from soybean plants sown in infested soil 245 days post-inoculation. 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. Colletotrichum truncatum microsclerotia in soil may serve as the primary inoculum source of soybean anthracnose.