Identification and characterization of Colletotrichum truncatum and C. destructivum causing stem rot of white clover in China

White clover (Trifolium repens L.) is an excellent quality forage legume species with superior planting efficiency, which reduces the cost of artificial weeding and nitrogen fertilizer inputs and has feeding and economic value. However, from June to September 2022, severe stem rot affected the yield and quality of white clover crops in Harbin, Heilongjiang Province, China. The aim of this study was to identify the causative agents of the disease. Overall, Colletotrichum truncatum (6 isolates) and C. destructivum (10 isolates) were obtained from rotten white clover stems and identified according to morpho-molecular characteristics and phylogenetic analyses. Pathogenicity tests of the isolates revealed that C. destructivum had a higher pathogenicity to white clover than C. truncatum. In addition, all isolates were highly pathogenic to broad bean, fodder soybean, soybean, pak choi, and chickpea, pathogenic to mint, and did not infect corn, wheat, or cilantro. C. destructivum and C. truncatum isolates were very sensitive to tebuconazole and pyraclostrobin, with EC50 values of 0.54 to 0.70 µg/ml and 0.42 to 0.62 µg/ml, respectively, efficacies ranging between 93.2 to 94.9% and 90.2 to 95.2% at 600 μg/ml and 450 μg/ml, respectively, and EC90 values of 1.88 to 13.36 µg/ml and 1.32 to 23.39 µg/ml, respectively. Therefore, intercropping of host and non-host plants and chemicals can be considered to control stem rot in white clover. These results provide a basis for controlling C. destructivum and C. truncatum in white clover in China.