Early blight, caused by different species of Alternaria, is a major and destructive disease of potato worldwide. In recent years, Alternaria tenuissima is recognized as the most prevalent species of this phytopathogenic fungus in potato fields of Asian countries, which causes high yield losses every year. Any potato cultivar with complete resistance to early blight is not recognized, so far. Therefore, screening resistance levels of potatoes, identification of the pathogen’s pathogenicity factors and plant defense mechanisms against the disease might be important for designing novel and effective disease management strategies. In this research, nine potato cultivars and five A. tenuissima isolates were used to investigate potential of these fungal isolates to infect various cultivars and determine resistance levels of the host plant. Cultivar Ramus had the highest level of resistance and Bamba was the most susceptible among all tested cultivars. Different levels of virulence and aggressiveness were observed for various isolates of A. tenuissima. Analyzing the activity of cell wall degrading enzymes (CWDEs), including cellulase, pectinase, lipase and xylanase produced by the fungal isolates revealed higher activity of these enzymes for the isolates with higher levels of pathogenicity on potato. Therefore, these findings suggested that activity levels of CWDEs, as pathogenicity factors, are correlated with virulence and aggressiveness of A. tenuissima on potato cultivars. This is the first report on screening host plant resistance, together with investigating association between pathogenicity factors and pathogenesis of A. tenuissima isolates, causing blight disease on potato.

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