Characterization of Fusarium species causing soybean root rot in Heilongjiang, China, and mechanism underlying the differences in sensitivity to DMI fungicides

Soybean root rot is a worldwide soil-borne disease threatening soybean production, causing large losses in soybean yield and quality. Fusarium species are the most detrimental pathogens of soybean root rot worldwide, causing large production losses. Fusarium root rot has been frequently reported in Heilongjiang Province of China, but the predominant Fusarium species and the sensitivity of these pathogens to different fungicides remain unclear. In this study, diseased soybean roots were collected from 14 regions of Heilongjiang province in 2021 and 2022. A total of 144 isolates of Fusarium spp. were isolated and identified as seven distinct species: F. scirpi, F. oxysporum, F. graminearum, F. clavum, F. acuminatum, F. avenaceum, and F. sporotrichioide. F. scirpi and F. oxysporum had high separation frequency and strong pathogenicity. The sensitivity of Fusarium spp. to five different fungicides was determined. Mefentrifluconazole and fludioxonil showed good inhibitory effects, and the sensitivity to pydiflumetofen and phenamacril varied between Fusarium species. In particular, the activity of DMI fungicide prothioconazole was lower than that of mefentrifluconazole. Molecular docking showed that mefentrifluconazole mainly bound to CYP51C, but prothioconazole mainly bound to CYP51B. Furthermore, the sensitivity to prothioconazole only significantly decreased in Delta FgCYP51B mutant, and the sensitivity to mefentrifluconazole changed in Delta FgCYP51C and Delta FgCYP51A mutants. The results demonstrated that the predominant Fusarium species causing soybean root rot in Heilongjiang province were F. scirpi and F. oxysporum and DMI fungicides had differences in binding cavity due to the diversity of CYP51 proteins in Fusarium.