| Summary: | Leaf spot disease in potato is caused by Alternaria alternata (Fr.) Keissler, an opportunistic pathogen that infests many agricultural crops worldwide in the field and during postharvest storage of vegetables and fruits. Alternaria alternata is associated with leaf spot disease in potato in Iran. Thus, there is a need to investigate the virulence and genetic variability of Iranian A. alternata isolates to facilitate the development of appropriate management strategies. In the present study, we analyzed a total of 28 isolates obtained from the main potato-growing regions of Iran, including the Ardebil, Hamedan, Isfahan, and Fars provinces. The pathogens were characterized based on sequence analysis of the genes encoding glyceraldehyde-3-phosphate dehydrogenase (gpd), plasma membrane ATPase, Alternaria allergen a 1 (Alt a1), calmodulin, and actin. In addition, random amplified polymorphic DNA (RAPD), intersimple sequence repeat (ISSR), and virulence studies were performed. Phylogenetic analysis of the combined dataset indicated that the five representative isolates were grouped with the subcluster comprising A. alternata. RAPD and ISSR analyses clustered the 28 A. alternata isolates into different groups with no correlation with their corresponding geographical origins. Results of the pathogenicity assay indicated that all A. alternata isolates were pathogenic against potato. However, the A. alternata isolates showed high variability in terms of virulence.
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