APS Homepage

Poster: Biology & Disease Mgmt: Chemical Control


Oxathiapiprolin baseline sensitivity distribution of Phytophthora capsici isolates.
G. OLAYA (1), R. Linley (2), K. Edlebeck (2), S. Kousik (3), P. Kuhn (4) (1) Syngenta, U.S.A.; (2) Syngenta, U.S.A.; (3) USDA-ARS, U.S. Vegetable Laboratory, U.S.A.; (4) Syngenta, U.S.A.

Oxathiapiprolin is the only active ingredient in a new class of fungicides (piperidinyl-thiazole-isoxazoline) that is active against downy mildews and Phytophthora species, and generally weak against Pythium species. It is active against multiple developmental stages of Oomycete fungi including inhibition of mycelial growth, sporangial germination, zoospore release, and zoospore germination. The proposed site of action is the inhibition of an oxysterol binding protein (OSBP). FRAC has assigned oxyathapiproline to group U15 and is considered to have a medium to high risk for resistance development. The oxathiapiprolin baseline sensitivity of Phytophthora capsici has been constructed using 40 isolates never exposed to this fungicide. P. capsici isolates were obtained from pepper, zucchini, squash, tomato, watermelon, pumpkin, smooth gourd, bitter gourd and an unknown host. Sensitivity tests were conducted in vitro using V8 agar media amended with oxathiapiprolin. Mycelial growth inhibition was quantified using the following oxathiapiprolin concentrations: 0, 0.000001, 0.00001, 0.0001, 0.001, 0.01 and 0.1 mg.ai/L. The baseline sensitivity distribution (ED50 values) of the P. capsici isolates ranged from 0.00006090 to 0.0005169 with a geometric mean of 0.00019716 mg oxathiapiprolin/L and a range of 8.5X. Oxathiapiprolin baseline information is critical for the early detection of resistant isolates and the establishment of effective resistance management recommendations.