Activity of the new OSBP inhibitor Y18501 against Pseudoperonospora cubensis and its application for the control of cucumber downy mildew.

Y18501 is a new oxysterol-binding protein inhibitor (OSBPI) with a similar structure to oxathiapiprolin. Y18501 showed strong inhibitory activities against Phytophthora spp. and Pseudoperonospora cubensis, with EC ranging from 0.0005 to 0.0046 μg/mL. It also had good control efficacy on cucumber downy mildew (CDM) in the green house and in the field, and could effectively inhibit different development stages of P. cubensis, especially for sporangiophore production, sporangial production, mycelium extension, and elongation of germ tube. In addition, Y18501 showed excellent protective and curative activities against P. cubensis. It also had acropetal systemic mobility in the cucumber leaves, and could be taken up and translocated to the upper leaves more effectively from the lower leaves than from the roots. Y18501 had poorer permeability in cucumber leaves compared to oxathiapiprolin. The simultaneous application of Y18501 and chlorothalonil could significantly promote the inhibition of P. cubensis.