Morphological and Molecular Characterization of Peronospora viciae Causing Downy Mildew on Field Pea and Vetch

Abstract

Downy mildew symptoms observed on field pea (Pisum sativum L.) and vetch (Vicia spp.) were investigated to determine the causal pathogen and characterize its morphological and molecular attributes. Field surveys conducted in legume-growing regions revealed chlorotic lesions, vein-limited yellowing, grayish-violet sporulation on the abaxial leaf surface, stunting, and reduced pod formation under cool and humid environmental conditions. Microscopic examination of infected tissues showed branched sporangiophores emerging through stomata and producing ovoid to ellipsoid sporangia typical of Peronospora viciae. Pathogenicity tests conducted on healthy pea and vetch seedlings under controlled humidity conditions successfully reproduced downy mildew symptoms, confirming virulence and fulfilling Koch’s postulates. Molecular identification using ITS rDNA and cytochrome oxidase subunit II (cox2) gene sequencing confirmed isolates as P. viciae, showing high similarity with reference sequences from global databases. Phylogenetic analysis placed all isolates within a well-supported P. viciae clade, indicating low genetic variability among populations infecting different host species. Observed sequence conservation suggests a relatively stable pathogen population with limited host-associated divergence. Disease development was strongly associated with prolonged leaf wetness, low temperatures, and high relative humidity, which favored sporulation and secondary spread. The study highlights the importance of P. viciae as a significant pathogen of cool-season legumes and emphasizes the need for accurate molecular diagnostics for early detection. Integrated disease management strategies, including resistant cultivars, crop rotation, and optimized irrigation practices, are recommended to reduce disease incidence and improve productivity in pea and vetch production systems.