Sensitivity of 40 Pythium species to the new fungicide Picarbutrazox

Abstract

Picarbutrazox is the active ingredient of Vayantis®, a novel seed treatment fungicide developed by Syngenta and discovered by Nippon Soda. Vayantis® received registration from the US EPA in 2021. Picarbutrazox is a systemic fungicide and belongs to the tetrazolyloximes chemical group of fungicides, and its mode of action is still unknown (FRAC group U17). Picarbutrazox targets oomycete plant pathogens and controls diseases caused by Pythium, Phytophthora, and downy mildews. Picarbutrazox is in a new mode-of-action group with no known cross-resistance to other oomycete compounds. The sensitivity to Picarbutrazox of 528 isolates belonging to 40 different Pythium species was determined in vitro. Pythium isolates were collected from infected plants including corn, soybean, cotton, and other crops from 17 different states. Pythium isolates were also obtained from collections kept at universities. Isolates were identified at the species level using morphological and molecular tools. Mycelial growth inhibition was quantified using the following Picarbutrazox concentrations: 0, 0.00001, 0.0001, 0.001, 0.01, and 0.1 mg/L. All the species of Pythium tested were sensitive to Picarbutrazox. The sensitivity distribution (EC50 values) across all the Pythium species tested had a mean sensitivity of 0.000376 mg ai/L. The Picarbutrazox sensitivity of 40 species of Pythium species has been documented, and results demonstrate the high in vitro intrinsic activity of this fungicide to control Pythium species. The high potency of Picarbutrazox to control Pythium diseases in corn, soybeans, cotton, and other crops has also been demonstrated under field conditions when used as a seed treatment. Picarbutrazox, with its novel mode of action, will contribute to the management of potential fungicide resistance issues developed by other fungicide products controlling Pythium, including mefenoxam and ethaboxam.