Response of Grapevine Cultivars to Powdery Mildew Disease in

  Identification of grapevine cultivars resistant to the powdery mildew disease has a main role in integrated management of the disease. In this study, the response of 45 native grapevine cultivars to powdery mildew, caused by Uncinula necator, was evaluated during 2003-2004, in West Azarbaijan proviance. After artificially inoculation of leaves of grapevine cultivars with conidia of the pathogen, abd completely development of the disease, severity index of disease was assessed on leaves and clusters of each cultivar . Results indicated that almost all of the cultivars were susceptible or highly susceptible to the disease. Among 45 cultivars, based on severity index of leaf, three cultivars Gharashani, Gharashirah and Aghshani, and based on severity index of cluster, cultivars Gharashani, Aghshani and Gharashirah were recognized as resistant cultivars. A negative significant correlation was found between the severity index of the infected clusters and fruits color in various cultivars. There was also a strong positive correlation between leaf and cluster infection and epicuticular wax of fruit. The chemical removal of fruit epicuticular wax, decresed resistance of grapevine cluster.