Virulence and Molecular Characterization of Erwinia pyrifoliae Strains Causing Shoot Blight on Asian Pear

Abstract

Shoot blight symptoms characterized by rapid shoot necrosis, blackening of blossoms, vascular discoloration, and twig dieback were observed in Asian pear orchards, leading to significant yield reduction and tree decline. Diseased shoot and blossom samples collected from affected orchards were used to isolate and characterize the associated bacterial pathogen through virulence assays and molecular techniques. Bacterial colonies obtained from infected tissues were creamy-white, smooth, and mucoid in appearance, consistent with characteristics of Erwinia pyrifoliae. Considerable variation in colony morphology and growth rate was observed among isolates collected from different orchard locations. Pathogenicity tests conducted on healthy pear shoots reproduced typical fire blight-like symptoms, including water-soaked lesions, rapid tissue collapse, and necrosis, confirming the virulence of the isolates. Re-isolation of the bacterium from inoculated tissues fulfilled Koch’s postulates. Molecular characterization was performed using amplification and sequencing of conserved housekeeping genes and 16S rRNA regions. Sequence analysis revealed high similarity between the obtained isolates and reference E. pyrifoliae strains deposited in international databases. Phylogenetic analysis grouped the isolates within the E. pyrifoliae clade, confirming species identity and revealing moderate genetic variation among strains from different geographic regions. Virulence assays indicated differential aggressiveness among isolates, suggesting variability in pathogenic potential within the population. Environmental conditions characterized by high humidity, moderate temperatures, and frequent rainfall significantly favored bacterial multiplication and disease spread in orchard systems. Infected trees exhibited reduced vegetative growth and substantial loss of productive shoots, impacting overall fruit yield. The integration of virulence testing and molecular characterization provided reliable identification of the pathogen and improved understanding of its epidemiology.