Reaction of different walnut cultivars to Gnomonia leptostyla, causal agent of walnut Anthracnose

Walnut Anthracnose caused by Gnomonia leptostyla (Fr.) Ces. & De Not. is one of the most serious foliar diseases of Persian walnut in absence of chemical treatments. The disease may result in premature defoliation, and fruit falling and reducing tree vigor and age in favorite conditions. Application of resistant cultivars is one of the main ways for disease management. In this study, interaction of different walnut cultivars were evaluated against this disease. An experiment was carried out in greenhouse condition as completely randomized block design with treatments and three replications. Conidia suspension of three fungus isolates with 0 per ml. concentration was atomized on seedling leaves which had been placed in three rows and columns arrangement. Seedlings incubated for 8 hours at ± oC in greenhouse under plastic covers and then the covers were removed. The seed plants were set around the grafted plants as guard. Macroscopic symptoms were occurred two weeks after primary inoculation. The numbers and diameter of spots were recorded one and two months after inoculation. Disease severity in seed cultivars was much more than grafted plants. According to the statistical analysis, Z67 and K7 cultivars showed more resistance in comparison with others and Z67 was the most resistant one. The cultivars Ser, Vina, Hartley, Ronde de Montignac, Lara and Franquett had moderate to weak resistance and the cultivars Z6, Z60 and Pedro were all susceptible to the disease.