Involvement of SIX9 in Growth and Pathogenicity in Fusarium oxysporum f. sp. fragariae

Strawberries, as an important economic crop, are widely planted worldwide. Fusarium oxysporum, belonging to FOSC (Fusarium oxysporum species complex), is widely present in plants. Among them, Fusarium oxysporum f. sp. fragariae (Fof) is one of the most important pathogens on strawberry and has pathogenic specificity toward strawberry hosts. In recent years, diseases caused by Fof have seriously threatened the strawberry industry. Secreted in Xylem (SIX) genes play important and different roles in F. oxysporum. In this study, we knocked out SIX9 in Fof to analyze its functions. The mycelial growth rate of ΔFofSIX9 was significantly lower than that of the wild type, but the difference in spore production was not significant. The pathogenicity of ΔFofSIX9 toward four different representative strawberry varieties was significantly reduced, manifested by the decrease in the severity of plant wilt, root rot, and crown rot. In addition, compared to the wild type, the activities of superoxide dismutase (SOD) and catalase (CAT) in ΔFofSIX9-infected plants were significantly increased, while the content of malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O2−) were significantly decreased. So ∆FofSIX9 could reduce the pathogenicity of the wild type by affecting the host plant’s defense response against infection of Fof.