In vitro sensitivity of Sclerotium rolfsii and four species of Trichoderma to common-use fungicides on the potato (Solanum tuberosum) crop

Background/Objective. Soft rot of potato tubers, caused by Sclerotium rolfsii, is a disease that occurs in soils with high levels of humidity and temperatures above 30 °C. Synthetic fungicides are primarily used for its control. The objectives of this study were to determine the biological efficacy of synthetic fungicides at different concentrations against the pathogen and the sensitivity of four species of Trichoderma to commonly used fungicides in potato in Sinaloa. Materials and Methods. The in vitro efficacy of nine fungicides at concentrations of 0.01, 0.1, 1, 10 and 100 ppm on mycelial growth inhibition and sclerotia formation of S. rolfsii was determined. Furthermore, the in vitro sensitivity of T. afroharzianum, T. asperelloides, T. asperellum, and T. azevedoi to 10 fungicides at concentrations of 100, 500, 1000, and 2000 ppm was studied. The experiment was conducted twice. Treatments were distributed in a completely randomized design and data were subjected to ANOVA. Means were compared with the Tukey test (p < 0.05). Results. Thifluzamide and Propineb at the 0.01 ppm concentration inhibited mycelial growth S. rolfsii by 32.7 and 12.2%, respectively. On the other hand, S. rolfsii produced 157, 164, and 164 sclerotia per Petri dish on PDA supplemented with the fungicides. Thifluzamide, Propineb and prochloraz, respectively, at the same concentration. In contrast, Propineb at a concentration of 100 ppm inhibited the mycelial growth of T. azevedoi, T. afroharzianum, T. asperellum and T. asperelloides by 0, 0, 0 and 54.9%, respectively; while the inhibition of mycelial growth by Thifluzamide at the same concentration in T. azevedoi, T. afroharzianum, T. asperellum and T. asperelloides ranged from 0 to 63%. The results indicate that the four Trichoderma species are compatible with both fungicides. Conclusion. The effect of thifluzamide and propineb on mycelial growth inhibition and sclerotia formation of S. rolfsii, as well as their compatibility with the four species Trichoderma, indicates that the combination of Trichoderma spp. and the fungicides has potential use for controlling soft rot of potato tubers under field conditions.