Virulence Characterization and Genomic Diversity of Erwinia amylovora Strains Causing Fire Blight in Apple and Pear

Abstract

Virulence characterization and genomic diversity of Erwinia amylovora strains causing fire blight in apple and pear were investigated to understand pathogen variability and its implications for disease epidemiology. Field surveys were conducted in affected orchards, and bacterial isolates were obtained from symptomatic tissues exhibiting shoot blight, blossom necrosis, and characteristic bacterial ooze. Virulence assays on detached shoots and immature fruits of apple and pear revealed significant variation in aggressiveness among strains, with certain isolates producing rapid lesion expansion and systemic infection, while others showed moderate pathogenicity. Molecular characterization was performed using whole-genome associated markers and gene-specific PCR targeting key pathogenicity determinants, including Type III secretion system (T3SS) genes. Genomic analysis indicated substantial genetic diversity among isolates, although core virulence genes were highly conserved. Phylogenetic clustering suggested the presence of distinct lineages with partial association to host species and geographic origin. Differences in virulence were strongly correlated with variation in effector gene repertoires and regulatory elements controlling pathogenicity. The study highlights the evolutionary adaptability of E. amylovora and its capacity for differential host colonization in pome fruit crops. These findings emphasize the importance of continuous genomic surveillance for early detection of highly virulent strains and support the development of integrated fire blight management strategies, including resistant cultivars and precision bactericide application programs to reduce disease impact in apple and pear production systems.