Аннотация
Alternariosis, caused by fungi of the genus Alternaria, has in recent years become one of the most widespread and economically significant diseases of apple (Malus domestica Borkh.). The disease poses a serious threat to commercial apple production, leading to yield losses and deterioration of fruit quality. Despite the widespread occurrence of the disease in apple orchards of Kazakhstan, the resistance level of domestic and foreign apple cultivars to the causal agent of alternariosis remains insufficiently investigated. Therefore, a comparative assessment of cultivar diversity in terms of resistance to this phytopathogen is of considerable scientific and practical relevance. The present study presents the results of evaluating the resistance of 23 domestic and foreign apple cultivars to alternariosis under natural epiphytotic conditions in southeastern Kazakhstan over two growing seasons. A clear differentiation among cultivars in disease severity was established. Cultivars characterized by relative resistance and of practical importance for breeding programs and commercial apple production were identified. According to the results, eight apple cultivars, including three developed by domestic breeding programs, were classified as having increased resistance (score 2, disease severity 1–10%), while fifteen cultivars were assigned to the moderately resistant group (score 3, 11–25%). No susceptible cultivars were identified under the conditions of this study.