Effect of d-pinitol isolated and identified from Robinia pseudoacacia against cucumber powdery mildew

• Active compound against cucumber powdery mildew was isolated from Robinia pseudoacacia extract.
• The active compound was identified to be d-pinitol.
• The control effect of d-pinitol was 80.7% at a concentration of 0.5 mg/ml in the growth chamber.
• d-Pinitol formulation was tested against cucumber and tobacco powdery mildew in the greenhouse.

The Robinia pseudoacacia plant extract has been reported to have protective effect against cucumber powdery mildew (Sphaerotheca fuliginea). In this study, the active compound of R. pseudoacacia was isolated from the plant extract, and the structure was identified to be d-Pinitol by nuclear magnetic resonance. d-Pinitol, as a known compound, has important physiological activity on plant osmotic tolerance and medicinal activities on human health. This study is the first to report the antifungal activity of d-pinitol on an obligate parasite S. fuliginea and tried to develop a phytochemical fungicide. The evaluation in the growth chamber showed that the control effect of d-pinitol and its formulation against cucumber powdery mildew disease was 80.7% and 94.4%, at a concentration of 0.5 mg/ml. This formulation was further tested in a greenhouse to evaluate its control effect against cucumber (S. fuliginea) and tobacco (Erysiphe cichoracearum) powdery mildew under natural condition. The efficacy of d-pinitol in both trials was better than that of positive control at the recommended concentration. The content of d-pinitol in this plant was 25 mg/g (w/w, dry leaves weight) as determined by gas chromatography. The abundant biomass of d-pinitol in R. pseudoacacia plant extract makes it more economical in practical use. Our study provides a base for the future exploitation of d-pinitol as a natural phytochemical fungicide.