ارزیابی واکنش لاین‌های سیب زمینی در برابر بیماری لکه موجی در شرایط تنش خشکی

Wave spot caused by Alternaria alternata is one of the significant diseases affecting potatoes, causing severe damage annually to this crop. The presence of biological stresses alongside environmental stressors can greatly reduce yield potential. Drought is among the most impactful environmental stressors on agricultural and horticultural productivity, and recent years of increased drought have led to reduced crop yields. The use of resistant varieties in breeding programs is one of the most effective and economical methods to prevent this disease. In this study, the reaction of 42 potato lines and two control varieties, Agria (susceptible) and Marfona (relatively resistant), was evaluated using strip plots under two irrigation methods: normal (control) and water stress (30% reduction), arranged in a randomized complete block design with three replications in both field and greenhouse conditions. Disease assessment in the field was conducted at two time points: post-flowering and late season, determining disease indices on a scale of 0 to 100 (0, 1-10, 11-25, 26-50, 51-75 and 76-100%). Statistical analysis was performed on the collected data. To assess tuber yield performance at the end of the growing season, weights were recorded. Additionally, morphological and molecular characteristics of 30 isolates of Alternaria fungus were identified using specific identification keys and gpd primers. The obtained sequences were compared with sequences in the gene bank, and a phylogenetic tree was constructed. Pathogenicity tests of these isolates were conducted in vitro and in the greenhouse on three potato varieties (Agria, Banba, and Sablan) in a completely randomized factorial design, and results were analyzed and scored. Results indicated significant differences among the tested lines at the 1% probability level. The highest and lowest disease severity was observed in the Marfona variety and line 8707.29, with mean values of 57.08% and 30.42%, respectively. The highest and lowest useful yield performance were observed in line 25/34-R3 and the Agria variety, respectively. Irrigation significantly increased total yield by 40% compared to the stress treatment. Comparison of Alternaria isolates with other sequences in the gene bank showed 99% similarity with Alternaria alternata species. Regarding the interaction effect of pathogenicity intensity of isolates and varieties, the highest disease severity was associated with the Sablan variety and isolate number 15, with a mean of 54.17%.