The FoPLT Gene of Fusarium oxysporum Affects Conidial Development and Pathogenicity

Apple replant disease (ARD) is a soil-borne disease that severely restricts root development in orchards, impedes tree growth, and leads to reduced yields and decreased fruit quality, and thus significant economic losses. Previous studies identified Fusarium oxysporum as a major pathogenic agent. In this study, a T-DNA insertion mutant library of 13,000 F. oxysporum HS2 strains was utilized to screen for mutants with impaired pathogenicity. Nine mutants exhibiting reduced virulence were obtained, and the insertion sites of five mutants were successfully identified. Among them, we selected the HS2-29 strain, which exhibited the most significant decrease in conidial production, for further investigation. Its T-DNA was inserted into the FoPLT gene. RT-qPCR analysis revealed that the expression of the FoPLT gene rapidly increased during the early infection stage, followed by a decline and eventual stabilization. After the deletion of the FoPLT gene, the production of aerial hyphae, conidial yield, conidial length, and conidial diameter all significantly decreased. Stress tolerance assays indicated that FoPLT does not affect cell wall integrity in F. oxysporum. The deletion of the FoPLT gene significantly reduced the pathogenicity of F. oxysporum, and inoculating Malus robusta seedlings with the FoPLT knockout mutant led to significant increases in plant height, root length, fresh weight, and dry weight. These results suggest that the FoPLT gene plays a critical role in the pathogenicity of F. oxysporum.