Effect of Different levels of Nitrogen and Potassium on Infection Severity of Canker of Apple Caused by Cytospora cincta Feries in Hydroponic Condition

Incidence and severity of various diseases in plants can be reduced by mineral nutrient management. To evaluate the effects of different levels of N and K on severity of infection of cytospora canker of apple trees, a factorial experiment based on randomized complete block design was conducted in greenhouse in a hydroponic system on two years old seedlings of apple cultivar Golden delicious. The experimental treatments consisted of four levels of N (0, 105, 210 and 315 mgkg-1) and K (0, 115, 230 and 345 mgkg-1), respectively. After six weeks, seedlings were inoculated with a highy pathogenic and virulent isolate of Cytospora cincta Fries, and six months later, mean lesion size on trunk of seedlings were measured. The results showed that changes in the amounts of N and K caused change in severity of infection. The highest and lowest severity of infection was observed in treatments whithout N (N0), K (K0) and optimal (N210K230) use of them. Severity of infection decreased with increasing of K level, while, with amounts less than optimum level of N (N210), severity of infection was variable, so that with amounts higher than optimum level, disease severity increased significantly. However by application of optimum levels of N and K, disease severity showed a significant decrease.