Biocontrol activity in a nonpathogenic REMI mutant of Fusarium oxysporum f. sp. conglutinans and characterization of its disrupted gene

Abstract

A nonpathogenic mutant (REMI10) of Fusarium oxysporum f. sp. conglutinans (FOC) was generated by restriction enzyme-mediated integration (REMI). REMI10 penetrated the cabbage root cortex much slower than FOC and never invaded the xylem through the endodermis. Previous treatment of cabbage seedlings with REMI10 reduced the disease incidence of yellows caused by FOC, suggesting that REMI10 has biocontrol activity. FOC invasion into root tissues was restricted when the seedling was treated with REMI10. The gene disrupted in REMI10 genome by plasmid insertion was identified, and designated sap1, which encodes a putative secreted aspartic proteinase. The sap1 disruptants showed no reduction in virulence toward cabbage, suggesting that SAP1 is not essential for pathogenicity in FOC.