P-115 - Screening of fungicides for managing propiconazole-resistant kernel smut of rice

Kernel smut of rice, caused by Tilletia horrida, is a seed-borne disease that can reduce rice yields by up to 30%. Disease symptoms are characterized by the replacement of rice grain with black, powdery teliospores. Management of kernel smut remains challenging due to the lack of fully resistant rice cultivars and the limited effectiveness of cultural practices. DMI fungicides, like propiconazole, are the most recommended treatment and have been heavily used in rice fields. However, recently the propiconazole-resistance populations of T. horrida have been identified in the U.S. In this study, we aimed to identify alternative fungicides for managing these resistant populations. In vitro assays were conducted using both propiconazole-sensitive and resistant isolates to evaluate the efficacy of multiple fungicides. Fungicides tested included dodine, fentin hydroxide, pydiflumetofen, thiophanate-methyl, mefentrifluconazole, benomyl, carbendazim, iprodione, triadimefon, fluazinam, tolclofos-methyl, fludioxonil, Revytek, Mirvis Top, Trivapro, Alto, Subdue Maxx, Actigard, and Mancozeb. Fungicide-amended potato dextrose agar media were prepared at concentrations of 0, 0.01, 0.1, 1.0, and 10 µg/ml. Among the tested fungicides, fluazinam and Trivapro demonstrated strong inhibitory effects against the propiconazole-resistant populations of T. horrida. These findings represent an important step in identifying alternative fungicides to propiconazole for the effective management of kernel smut in rice.