Isolation and Molecular Characterization of Cercospora capsici Heald and F. A. Wolf Infecting Capsicum annuum var grossum Sendt

Abstract

Background: Cercospora leaf spot is a significant disease affecting bell pepper in Karnataka, India, and is caused by Cercospora capsici. The pathogen is characterized by the development of distinct necrotic lesions on foliar tissues, which often progress to severe defoliation and consequent yield losses. Identification of the causal organism was undertaken through comprehensive morphological and cultural analyses, including colony characteristics, the structure of conidiophores, and the production of hyaline, elongated, multiseptate conidia, which are diagnostic features of the genus Cercospora. Aim: The present study was undertaken to study the severity of leaf spot disease of capsicum (Capsicum annuum L. var. grossum) in southern Karnataka, India, its etiology and morphological and molecular characterization of the casual organism. Methodology: Diseased leaf samples collected from major capsicum-growing regions were subjected to pathogen isolation and characterization. The causal organism was identified using an integrated approach combining morphological and cultural characteristics with multilocus sequence analysis based on the internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF1-α), and calmodulin (CAL) gene regions. Results: In a roving survey conducted in Bengaluru Rural, Chikkaballpur and Kolar districts of southern Karnataka during the year 2021-22 and 2022-23, Bengaluru rural district recorded the highest severity of Cercospora leaf spot (27.13%). Phylogenetic analysis of the concatenated multilocus dataset provided robust species-level resolution and confirmed the pathogen as Cercospora capsici. All the three isolates formed a common clade with the representative isolates obtained from Genbank with the bootstrap values of >75.00% to 99.00% and a least evolutionary distance of <0.0001. Pathogenicity of the representative isolates was successfully established through Koch’s postulates. Isolates obtained from Bengaluru, Chikkaballapur, and Kolar exhibited high morphological similarity and clustered together with strong phylogenetic support, indicating genetic uniformity among regional populations. The multilocus-based characterization further confirmed the host specificity of C. capsici infecting capsicum. Conclusion: This study provides a comprehensive identification and phylogenetic delineation of the leaf spot pathogen infecting capsicum, contributing to a clearer understanding of Cercospora species diversity and host specificity in the region.