First Report and Koch's Postulates Confirmation of Plectosphaerella cucumerina Causing Crown Rot on Pepper

Abstract

Pepper is an economically important vegetable crop cultivated widely under open-field and protected cultivation systems; however, its production is threatened by several soil-borne fungal pathogens that reduce plant vigor and yield. During recent disease surveys, pepper plants exhibiting crown rot symptoms, including stem discoloration, basal necrosis, wilting, and plant collapse, were observed in commercial production fields. The present study was conducted to identify and confirm the causal agent associated with crown rot disease of pepper through morphological, molecular, and pathogenicity analyses. Diseased plant tissues were collected from symptomatic pepper plants, and fungal isolates were obtained using standard isolation techniques on selective culture media. Morphological characterization of the isolates was performed based on colony appearance, hyphal morphology, and conidial characteristics. Molecular identification was carried out through polymerase chain reaction (PCR) amplification and sequencing of conserved genomic regions, followed by sequence comparison and phylogenetic analysis. Pathogenicity assays were conducted under controlled greenhouse conditions by inoculating healthy pepper seedlings with representative fungal isolates to verify disease development and fulfill Koch’s postulates. The results consistently associated Plectosphaerella cucumerina with crown rot symptoms observed in infected pepper plants. Inoculated seedlings developed characteristic symptoms including crown necrosis, wilting, and root discoloration similar to those observed in naturally infected plants, while control plants remained healthy. The pathogen was successfully re-isolated from inoculated plants, thereby confirming Koch’s postulates. Molecular sequence analysis revealed high genetic similarity between the obtained isolates and previously reported P. cucumerina strains from other hosts and geographic regions. This study represents the first report of Plectosphaerella cucumerina causing crown rot disease on pepper in the studied region.