Reaction of Promising Walnut Hybrids to Black Spot Disease (Ophiognomonia leptostyla)

Black spot disease (Ophiognomonia leptostyla) is an important disease in walnut growing areas all over the world. Four promising walnut hybrids; H 1-1, H 1-7, H 2-12 and H 2-1 were evaluated for susceptibility to using factorial arrangement in completely randomized design. Hartley and K72 were included as resistant and susceptible controls, respectively. The experiment was conducted in spring 2021 and 2022. Fully expanded walnut leaflets were inoculated by fungal conidia (105 spore ml-1). Number and size of necrotic spots were recorded at 15-day intervals until 45 days after inoculation. According to the data of 45 days after inoculation, the maximum number of necrotic spots belonged to H 2-12 while the largest spots were developed on H 1-1 and H 1-7. First acervuli appearance was occurred 43-44 days after inoculation on H 1-1 and H 2-12. All evaluated hybrids were susceptible, but symptoms development and disease severity varied. The average of NLA ranged from 20% in Hartley to 90% in H 1-7. H 1-7, H 1-1 and H 2-12 as well as K72 exhibited high level of infection and was considered as highly susceptible. Hybrid H 2-1 with the average NLA of 52% was classified in moderately susceptible group.