Study of Effects of Grape Powdery Mildew Disease (Erysiphe necator) on the Yield and Quality of Grape

Powdery mildew caused by Erysiphe necator Schw. is one of the most economically destructive diseases of grapevines all over the world including Iran. In this experiment، The effects of powdery mildew on grape yield، sugar and tartaric acid contents of must quality were quantified for different grapes with 14 cultivars of grapes including Shahani، Kishmishi، Rasmi، Tokolgan، Garashilig، Seyrakpousteh، Khalili، Tabarzeh، Koupakbogan، Aldarag، Sahibi، Agshilig، Yagothi and Tabrizkishmishi were examined in natural infection during 2009-2010 in Ardabil province. Sugar and tartaric acid contents in grape were measured by a hand refractometer and titration with 0. 1 M sodium hydroxide respectively. Analysis were carried out on diseased and healthy berries، which these were classified into six classes from low (0) to high (5) disease severity. Highly susceptible and susceptible cultivars diseased berries showed at most weight reduction in yield. Diseased berries had a higher sugar and acid contents than disease-free berries.