Abstract:Tricyclazole (5-methyl-1,2,4-triazol[3,4]benzothiazole), a specific inhibitor of DHN melanin biosynthesis, was used to clarify its effects on the pathogenicity of Setosphaeria turcica. Melanin content, pore size, turgor pressure of appresoria and pathogenicity were analyzed with poison media. The results showed that tricyclazole under 5μg/mL had no inhibiting ability on hyphal growth and conidial production, but melanin biosynthesis and infection ratio were dropped to 43% and 37.5%, respectively. Appressorium pore was enlarged to 2.7-3.3nm, while turgor pressure of appresorium was decreased to 3.75MPa, resulting in lesions on susceptible host reduced greatly. Those results indicated that tricyclazole reduced the pathogenicity of S.turcica by inhibiting DHN melanin biosynthesis and turgor pressure of appresoria.