LAUSR

BACKGROUND Mineral oils have been widely used in the pest control of several crops. However, their mode of action is poorly understood, especially in the case of their antifungal properties. The possible direct fungicidal activity and the stress-inducing capability of paraffin oil on grapevine were examined using Vitis vinifera L. cv 'Kékfrankos' cuttings and the fungus Erysiphe necator the causal agent of powdery mildew. RESULTS Our experiments demonstrated that paraffin oil does not have fungicide activity on E. necator, but induces significant stress-related changes in grapevine physiology. Elevated H2 O2 production and the accumulation of the phytohormone salicylic acid were measured. Secondary thickening of the cell wall by lignin deposition and the accumulation of phenolic compounds were also observed. Some enzyme activities related to the detoxification of reactive oxygen species, disease response, and the synthesis of lignin were changed in accordance with the determined changes in cell wall composition and H2 O2 levels. CONCLUSION The results suggest that paraffin oil induces stress responses on grapevine leaves through oxidative burst, which response is systemized by salicylic acid. The accumulation of lignin and water-soluble phenolics may be directly responsible for the paraffin oil-induced resistance of grapevine against powdery mildew. This article is protected by copyright. All rights reserved.