Walnut blight resistance in the genus Juglans

Walnut blight is considered one of the most serious above ground diseases of the genus Juglans. It occurs in all walnut-growing areas, although it can cause epidemics only in certain zones and years in relation to the climatic conditions and to walnut species and variety. In this work several Juglans species and J. regia varieties were investigated for their resistance to the disease. Mass selection was carried out on J. cinerea, J. hindsii, J. nigra, J. sieboldiana, J. sieboldiana var. cordiformis and Italian J. regia varieties, namely Feltre, Malizia, Sorrento as well as the Southern local cultivar Decollatura. Artificial inoculations were performed by spraying the seedlings to run off. Resistance in J. regia plantlets var. Feltre, Franquette, Hartley, Malizia, Payne, Serr and Sorrento was assessed by injecting a bacterial suspension into the stem. Among Juglans spp. and English walnut varieties sprayed, J. nigra, J. cinerea and J. sieboldiana proved to be highly resistant. Among English walnut varieties infected by injection, Franquette and Hartley were the most resistant, Feltre and Malizia showed an intermediate susceptibility while Payne, Serr and Sorrento proved the most susceptible.