Identification and pathogenicity of Clonostachys spp. and its co-inoculation with Fusarium species on soybean root

Soybean is an important protein and oil crop around the world, widely cultivated in Heilongjiang province, China. In the summer of 2021, soybean root rot samples were collected from farms in multiple regions of Heilongjiang province to isolate pathogens. Twenty-seven fungal isolates with similar morphology were found, causing soybean root discolouration and blackness leading to root rot, but which had relatively mild pathogenicity, with an average disease index of 13.69-32.25. Morphological features and multilocus phylogenetic analyses divided these isolates into four species: Clonostachys rosea (48.2%), C. rosea f. sp. rosea (14.8%), C. chloroleuca (29.6%) and Clonostachys sp. (7.4%). Co-inoculation of these four species with two important pathogenic Fusarium species that can cause soybean root rot, F. annulatum and Fusarium sp. 1 in the Fusarium oxysporum species complex (FOSC), showed that C. rosea and Clonostachys sp. significantly reduced the pathogenicity of F. annulatum to soybean root, while C. rosea f. sp. rosea and C. chloroleuca slightly increased the pathogenicity of F. annulatum. C. rosea, Clonostachys sp., C. chloroleuca and C. rosea f. sp. rosea slightly reduced the pathogenicity of Fusarium sp. 1 in the FOSC. Our research is the first to report Clonostachys sp., C. chloroleuca and C. rosea f. sp. rosea causing soybean root rot in Heilongjiang province, China, and that these four Clonostachys species can affect the pathogenicity of Fusarium species, alleviating or aggravating soybean root rot. The findings of this study provide new insights into exploring the interactions between pathogens and thus effectively controlling them.