Morphological and Molecular Identification of Rhizoctonia solani Anastomosis Groups Causing Damping-Off in Vegetable Seedlings

Abstract

Damping-off disease caused by Rhizoctonia solani is a major constraint in vegetable seedling production, leading to poor germination, seedling mortality, and reduced stand establishment in nurseries and field transplant systems. The present study aimed to characterize the morphological and molecular diversity of R. solani anastomosis groups (AGs) associated with damping-off in vegetable seedlings. Diseased seedlings showing pre- and post-emergence damping-off symptoms were collected from different vegetable-growing regions, and fungal isolates were obtained using standard isolation techniques. Morphological characterization was performed based on colony growth pattern, hyphal branching, presence of right-angled branching, constriction at the branch point, and sclerotia formation. Considerable variation in cultural and morphological traits was observed among isolates, suggesting diversity within the pathogen population. Molecular identification was carried out using PCR amplification of ribosomal DNA regions followed by sequencing and phylogenetic analysis to determine anastomosis groups. The results confirmed the presence of multiple R. solani AGs associated with vegetable seedling damping-off, with distinct clustering patterns observed among isolates. Certain AGs were more frequently associated with severe disease incidence, indicating higher pathogenic potential and adaptability to nursery environments. Variability in virulence among isolates suggested differences in host specificity and environmental adaptation. The integration of morphological and molecular approaches provided accurate identification and classification of R. solani populations. The findings highlight the complex etiology of damping-off disease and emphasize the importance of understanding AG distribution for effective disease management. This study provides valuable information for nursery sanitation, crop rotation strategies, and the development of integrated disease management programs aimed at reducing damping-off incidence in vegetable production systems.