Effects of Sunflower Oil on Tomato Powdery Mildew Caused by Oidium neolycopersici

When tomato leaves were sprayed with 0.1% emulsified canola oil, corn oil, grape seed oil, peanut oil, safflower oil, soya bean oil or sunflower oil, the severity of powderymil dew caused by Oidium neolycopersici was greatlyredu ced. Among these edible oils tested, sunflower oil was the most effective in the control of powderymild ew. When sprayed with 0.5% sunflower oil, powderymil dew on tomato leaves was reduced to a negligible level. Sunflower oil applied to halves of upper leaf surface did not induce resistance against the pathogen in the non-treated halves. When applied to halves of lower leaf surface, it also failed to reduce the severityof powderymildew on the upper leaf surface right above the treated area indicating that control of the powderymildew bysunflo wer oil did not result from activation of host defence mechanisms. Scanning electron microscopyshowe d that control of powdery mildew with sunflower oil resulted mainlyfrom the inhibition of conidial germination and suppression of mycelial growth of the pathogen