Alternaria brassicicola-induced postharvest head blight of cabbage: Insights into its pathogenicity and host range potential on crucifer crops

Alternaria brassicicola, a prevalent necrotrophic fungal pathogen of Brassica species, infects above-ground plant parts in fields and postharvest. We observed an unusual case of head blight disease in cabbage from a market in Mohali, India. Symptomatic samples were collected and subjected to etiological and molecular investigations. Ten morphologically similar fungal isolates were isolated, and one isolate, CAbc, was comprehensively characterized. Radial growth assays on nutrient-rich media indicated that the isolate CAbc thrived and sporulated at 5–30 °C and pH 3.0–10, indicating potential for survival and re-emergence. In vitro assays demonstrated that the isolate CAbc induced typical head blight symptoms, leading to complete cabbage head decay. Pathogenicity tests on detached and intact cabbage leaves and foliar inoculation confirmed characteristic leaf blight symptoms, accelerated senescence, and leaf withering, fulfilling Koch's postulates. Multilocus sequence analysis confirmed A. brassicicola as the causative pathogen. Phylogenetic analysis using five marker genes of A. brassicicola isolates revealed that the isolate CAbc clustered with the type strain ATCC 96836 (EG Simmons). Host range assays demonstrated consistent virulence on cauliflower (Brassica oleracea var. botrytis) and oilseed mustard (B. juncea subsp. juncea). The pathogen caused severe leaf blight under various in vitro and in planta inoculation trials. These findings suggested that the isolate CAbc, originally isolated from cabbage, exhibits a broad host range among other cruciferous crops. Collectively, our findings provided insights into the pathogen's identity, growth tolerance, pathogenicity, genetic relationships, infection-related histopathology, and host range, which might help guide pre- and postharvest disease management strategies.