Morphological and Molecular Characterization of Plenodomus lingam Causing Blackleg Disease on Canola

Abstract

Blackleg disease symptoms observed on canola (Brassica napus L.) were investigated to identify the causal pathogen and characterize its morphological and molecular features. Field surveys revealed characteristic symptoms including leaf lesions with pale centers and dark margins, stem cankers, internal vascular discoloration, and premature plant lodging, leading to significant yield reduction under conducive environmental conditions. Fungal isolates obtained from infected stem and leaf tissues produced slow-growing colonies with gray to dark pigmentation and abundant pycnidia on potato dextrose agar. Microscopic examination revealed hyaline, cylindrical to ellipsoid conidia consistent with Plenodomus lingam. Pathogenicity tests conducted on susceptible canola seedlings under controlled conditions successfully reproduced blackleg symptoms, confirming virulence and fulfilling Koch’s postulates. Molecular identification using ITS rDNA, β-tubulin, and actin gene sequencing confirmed isolates as P. lingam, showing high sequence similarity with reference strains in global databases. Phylogenetic analysis placed all isolates within a well-supported Plenodomus lingam clade, indicating limited but detectable genetic variation among regional populations. Observed minor nucleotide polymorphisms suggest possible adaptation to local climatic and host conditions. Disease severity was strongly associated with cool, moist environments and extended leaf wetness periods, which facilitated infection and systemic colonization. The study highlights the continued importance of P. lingam as a major pathogen of canola and emphasizes the need for accurate molecular diagnostics for early detection and epidemiological monitoring. Integrated disease management strategies, including crop rotation, resistant cultivars, residue management, and timely fungicide application, are recommended to reduce disease incidence and improve canola productivity under diverse agro-climatic conditions.