Evaluation and fungicide sensitivity of Colletotrichum sojae causing root rot in soybean in Northeast China

Soybean (Glycine max L.) is a globally significant oil crop with a pivotal role in the economic development of nations. In 2023, an unusual outbreak of soybean root rot (SRR) was observed in Harbin, Heilongjiang Province, China. Colletotrichum sojae infects soybean roots, leading to root rot symptoms. Using the tissue isolation method, a total of 22 fungal isolates were obtained, among which five representative pathogenic strains were identified as C. sojae. The remaining 17 strains are common Fusarium oxysporum and Phomopsis species that have been previously reported in the Heilongjiang region. To the best of our knowledge, this is the first report of SRR caused by C. sojae in China. Additionally, C. sojae exhibited a broad host range, causing root rot in most tested legumes, but did not infect maize or mung bean. Fungicide susceptibility assays revealed that C. sojae isolates were most sensitive to prochloraz, with an EC50 value of 0.0031 μg/mL. In two independent greenhouse pot experiments, the average control efficacy of 0.45 mg/mL prochloraz against SRR caused by C. sojae was 81.3%. Our results provide a theoretical foundation for managing SRR in this region and contribute to the development of effective disease control strategies.