Morphological and Molecular Characterization of Alternaria infectoria Causing Black Point Disease on Wheat Grain

Abstract

Black point disease symptoms observed on wheat (Triticum aestivum L.) grains were investigated to identify the causal pathogen and characterize its morphological and molecular attributes. Field and post-harvest grain samples exhibiting dark discoloration at the embryo end were collected from major wheat-growing regions and subjected to fungal isolation and analysis. Cultures obtained from infected grains produced slow to moderately fast-growing colonies with olivaceous to dark gray pigmentation on potato dextrose agar, along with septate, branched mycelium typical of Alternaria species. Microscopic examination revealed small, obclavate to ellipsoid, septate conidia consistent with Alternaria infectoria. Pathogenicity tests conducted on healthy wheat spikes under controlled conditions successfully reproduced black point symptoms, confirming the virulence of the isolates and fulfilling Koch’s postulates. Molecular identification using ITS rDNA, GAPDH, and Alt a 1 gene sequencing confirmed isolates as A. infectoria, showing high similarity with reference sequences in global databases. Phylogenetic analysis placed all isolates within a well-supported A. infectoria clade, indicating limited genetic variation among populations from different regions. Minor sequence polymorphisms suggested possible adaptation to environmental conditions and grain storage environments. Disease incidence was associated with high humidity during grain filling and delayed harvesting, which favored fungal colonization. The study highlights the significance of A. infectoria as a grain quality-reducing pathogen in wheat production systems and emphasizes the need for integrated disease management strategies. Timely harvesting, improved post-harvest handling, and field sanitation are recommended to reduce black point incidence and maintain grain quality in wheat.