First Comprehensive Morphological, Pathogenic and Molecular Characterisation of <scp> <i>Alternaria alternata</i> </scp> Associated With Leaf Spot of <scp> <i>Pyrus communis</i> </scp> in Punjab, India

ABSTRACT Pear ( Pyrus communis ) is an important fruit crop in India, and its productivity is increasingly threatened by leaf spot disease caused by Alternaria alternata . To investigate the prevalence and characterise the causal agent, surveys were conducted during 2023 across seven major pear‐growing districts of Punjab. Forty fungal isolates were recovered from symptomatic leaves and characterised based on cultural and morphological traits. Pathogenicity tests under both in vitro and field conditions confirmed their virulence, with isolates A1 and A15 showing the shortest incubation period, fastest lesion expansion and highest disease severity. Successful re‐isolation of the pathogen from infected tissues fulfilled Koch's postulates. Three highly virulent isolates (A1, A14, A15) were further subjected to multilocus sequence analysis using the Internal Transcribed Spacer (ITS), Small Subunit ribosomal RNA (SSU), Large Subunit ribosomal RNA (LSU), glyceraldehyde‐3‐phosphate dehydrogenase (gapdh), translation elongation factor 1‐alpha (tef‐1α) and RNA polymerase II subunit (rpb2) gene regions. Phylogenetic analysis clustered these isolates with reference A. alternata strains, confirming their identity. This study represents the first comprehensive morphological, pathogenic and molecular characterisation of A. alternata causing leaf spot of pear in Punjab, providing a foundation for disease monitoring and management strategies.