Intraction between rootstock and variety in response to causal agent of apple powdery midew Podosphaera leucotricha

Apple powdery mildew is one of the most important apple diseases (Malus domestica Borkh) in the world. The aim of this study was to evaluate interaction effects between some common cultivars and rootstocks to apple powdery mildew. The experiment was conducted in a factorial randomized block design with four replications under natural conditions using MM.111, MM.106, M9 seedling rootstock and four cultivars include Red Delicious, Golden Delcious, Golab e Kohanz and Golab e Esfahan, in four years. The evaluation was performed based on incidence and severity disease percentage on the leaves during two years. It was concluded that M.9 rootstock have a negative effect on Esfahan's Golab and made the cultivar more susceptible to the disease.  However, this rootstock had a positive effect on Red Delicious, Golden Delicious and Golab e Kohanz. M.9 × Golab e Esfahan and Seedling × Golab e Esfahan combinations with 52.% and 48.10% disease incidence and 56.77 and 53.33 disease severity percentage respectively, showed the most suceptibility, while, M.9 × Red Delicious and MM.106 × Red Delicious with 12.50 %and 16.76% disease incidence and 16.47% and 19.61% disease severity respectively, showed the highest resistance. So Golab e Kohanz and Red Delicious on M.9 rootstock, Red Delicious on M.9 and M.106 rootstock are recommended.