Antifungal activity of the combination of thifuzamide and pyraclostrobin against Rhizoctonia solani and its indoor control efficacy against tobacco target spot

Tobacco target spot (TTS) caused by Rhizoctonia solani is one of the major leaf diseases in tobacco in recent years, which significantly reduces the yield and quality of tobacco. However, only validamycin has been registered for TTS control to date, however, its curative activity in fields is relatively low. To screen chemical fungicides with high antifungal activity against R. solani, the sensitivity baseline of R. solani to thifuzamide and pyraclostrobin was established by the mycelium growth inhibition assay, respectively. When tested alone, both thifuzamide and pyraclostrobin exhibited high antifungal activity against R. solani mycelial growth. The allied toxicity assays showed that the combinations of thifuzamide and pyraclostrobin have either additive or synergistic effects. A mixture of thifuzamide and pyraclostrobin (m/m, 1 : 1) exhibited the best synergistic inhibition of mycelial growth with a synergistic coefficient of above 2.5 and significantly inhibited the formation of sclerotium. The spray inoculation method was used to evaluate the protective and curative activities of the mixture to TTS and the result showed that the mixture has excellent indoor control efficiency. Taken together, these results indicated that a mixture of thifuzamide and pyraclostrobin (m/m, 1 : 1) had good potential in TTS control in the fields.