Morphological and Molecular Characterization of Pomegranate Fruit Black Spot and Heart Rot Pathogen, Alternaria alternata, and its Virulence Factors
DOI:
https://doi.org/10.66167/ijlsci/2025113261Keywords:
Alternaria alternata, Pomegranate, ITS Sequencing, Phylogeny, Extracellular Enzymes, Virulence FactorsAbstract
Alternaria alternata emerges as a prominent fungal pathogen affecting pomegranate (Punica granatum L.), especially in Maharashtra, India. In this study, symptomatic fruits exhibiting black spots and rot were collected from orchards in the Jalna district, from which the causal fungus was isolated onto potato dextrose agar (PDA) medium, designated as isolate AAPI01. Pathogenicity tests confirmed the isolate's virulence, as it produced characteristic rot lesions on inoculated healthy fruits. Morphological characterization revealed the presence of septate hyphae and muriform conidia, which are typical for A. alternata. Molecular identification was achieved through amplification and sequencing of the ITS region, with subsequent BLAST analysis affirming its taxonomic classification as A. alternata. Phylogenetic analysis, utilizing the Neighbor-Joining method, positioned AAPI01 in close relation to reference strains of A. alternata, supported by a bootstrap confidence of 53%. In vitro assays of extracellular enzymes demonstrated the secretion of four hydrolytic enzymes, with pectinase (21.4 ± 0.8 mm) exhibiting the highest activity, followed by xylanase (18.6 ± 0.5 mm) and cellulase (15.2 ± 0.6 mm) at moderate levels, while protease (12.5 ± 0.4 mm) showed comparatively lower activity. These findings underscore the central role of pectinase in cell wall degradation, which initiates tissue maceration, while cellulase and xylanase act synergistically to facilitate colonization, and protease contributes to the weakening of host defenses.
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