Abstract
Leaf spot disease in potato is caused by <em>Alternaria alternata</em> (Fr.) Keissler, an opportunistic pathogen that infests many agricultural crops worldwide in the field and during postharvest storage of vegetables and fruits. <em>Alternaria alternata</em> is associated with leaf spot disease in potato in Iran. Thus, there is a need to investigate the virulence and genetic variability of Iranian <em>A. alternata</em> 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 (<em>gpd</em>), plasma membrane ATPase, <em>Alternaria</em> 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 <em>A. alternata</em>. RAPD and ISSR analyses clustered the 28 <em>A. alternata</em> isolates into different groups with no correlation with their corresponding geographical origins. Results of the pathogenicity assay indicated that all <em>A. alternata</em> isolates were pathogenic against potato. However, the <em>A. alternata</em> isolates showed high variability in terms of virulence.
Highlights
Alternaria alternata (Fr.) Keissler has been isolated from a wide range of crops, including fruits and vegetables, nuts, and cereals [1]
Molecular approaches based on sequence analysis of gene fragments encoding glyceraldehyde-3-phosphate dehydrogenase, plasma membrane ATPase, Alternaria allergen a 1 (Alt a1), calmodulin, and actin have robustly defined the monophyly of Alternaria in the ascomycete family Pleosporaceae [5]
Our findings indicated that both random amplified polymorphic DNA (RAPD) and intersimple sequence repeat (ISSR) markers can be used to reliably evaluate the diversity of A. alternata isolates
Summary
Alternaria alternata (Fr.) Keissler has been isolated from a wide range of crops, including fruits and vegetables, nuts, and cereals [1]. A. alternata is a common saprobe found in many plants and other substrata worldwide and is an opportunistic pathogen that infects many agricultural crops in the field and during postharvest storage of vegetables and fruits. The A. alternata fungus causes brown necrotic lesions in foliage and black pit [2]. Previous reports have shown that A. alternata can destroy more than 20% of potato production [3,4]. Multigene phylogeny has been widely employed for identification and characterization of Alternaria species [6,7].
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