Diversity and pathogenicity of Stemphylium and Alternaria species associated with foliar blights in rainfed legumes of Iran

Abstract

Foliar blights threaten rainfed cool-season legumes in Iran, but the diversity and pathogenicity of the associated Stemphylium and Alternaria species remains poorly characterized. This study characterized 98 fungal isolates obtained from symptomatic chickpea, lentil, grass pea, and vetches plants collected across eight provinces in western and northwestern Iran. Based on morphological characteristics and gapdh sequencing of all isolates, followed by multi-locus phylogenetic analysis (gapdh and cmd for Stemphylium; gapdh, rpb2, tef1, and Alt a 1 for Alternaria) of representative isolates, five Stemphylium and five Alternaria species were identified. This included first reports of S. amaranthi on lentil, S. lycii on chickpea and lentile, A. atra and A. consortialis on chickpea, lentil and vetches, and A. japonica on chickpea. Stemphylium species, predominantly S. vesicarium and S. beticola, were mainly recovered from lentil. Alternaria species, dominated by A. alternata, occurred on all four hosts. Pathogenicity assays confirmed all species as pathogenic, with aggressiveness varying by host and species. Common vetch was highly susceptible, whereas grass pea displayed partial resistance. A key finding was the frequent co-occurrence of Stemphylium and Alternaria species in chickpea and lentil, revealing that foliar blight in these crops operates as a disease complex rather than a single-pathogen disease. This complexity, where interactive pathogen dynamics likely drive disease severity, challenges conventional management. Our findings redefine the etiology of legume blights in Iran and underscore the need for integrated, region-specific control strategies that target the entire pathogen community.