Etiology and Pathogenicity of Stemphylium vesicarium Causing Brown Spot Disease on Pear in Temperate Orchards

Abstract

Brown spot disease caused by Stemphylium vesicarium is an emerging fungal disease of pear that poses a serious threat to fruit production in temperate orchard systems. The disease affects leaves, shoots, and fruits, resulting in necrotic lesions, premature defoliation, fruit blemishes, and significant reductions in yield and market quality. Favorable environmental conditions such as prolonged humidity and moderate temperatures contribute to rapid disease development and spread in orchards. The present study was conducted to investigate the etiology and pathogenicity of S. vesicarium associated with brown spot disease of pear in temperate production regions. Symptomatic pear tissues exhibiting characteristic brown lesions were collected from affected orchards, and fungal isolates were obtained using standard isolation techniques. Morphological characterization was performed based on colony morphology, conidial structures, and cultural characteristics, while pathogenicity assays were conducted under controlled conditions to confirm the causal role of the pathogen. Healthy pear leaves and fruits were artificially inoculated with representative isolates, and symptom development was monitored to fulfill Koch’s postulates. Molecular identification was further carried out using polymerase chain reaction (PCR) amplification and sequencing of conserved genomic regions to confirm species identity. The results consistently associated S. vesicarium with brown spot symptoms observed in infected pear orchards. Inoculated plant tissues developed characteristic necrotic lesions similar to those observed under natural field conditions, confirming the pathogenicity of the fungus. Molecular sequence analysis revealed high similarity between the obtained isolates and previously reported S. vesicarium strains affecting pear and related hosts. Disease severity was found to increase under humid environmental conditions, indicating the importance of climatic factors in disease epidemiology. The findings of this study provide important insights into the biology, pathogenicity, and identification of S. vesicarium affecting pear orchards. Accurate diagnosis and understanding of pathogen behavior are essential for developing effective disease management strategies aimed at minimizing economic losses and improving sustainable pear production in temperate regions.