Virulence and Cultural Characteristics of Rhizoctonia zeae Causing Sheath Blight on Maize in Humid Tropical Regions

Abstract

Rhizoctonia zeae is an important soil-borne fungal pathogen associated with sheath blight disease in Maize, particularly under warm and humid environmental conditions prevalent in tropical regions. The present investigation was conducted to study the virulence and cultural characteristics of R. zeae isolates collected from maize-growing areas exhibiting typical sheath blight symptoms, including water-soaked lesions, sheath discoloration, and premature drying of leaves. Diseased samples were collected from different humid tropical regions, and the pathogen was isolated using standard tissue culture techniques. Morphological and cultural variability among isolates was assessed on potato dextrose agar (PDA) medium based on colony color, growth rate, mycelial texture, sclerotial production, and pigmentation. Considerable variation was observed among isolates with respect to colony morphology and growth behavior. Pathogenicity tests conducted under greenhouse conditions confirmed the ability of the isolates to induce sheath blight symptoms on healthy maize plants. Virulence studies revealed significant differences among isolates in lesion development, disease severity, and host colonization capacity. Highly virulent isolates produced extensive lesions and rapid tissue necrosis compared to moderately virulent isolates. Environmental factors such as high humidity and temperature were found to favor pathogen growth and disease development. The observed variability in cultural and virulence characteristics suggests the existence of diverse populations of R. zeae in tropical maize ecosystems. Understanding the pathogenic diversity and growth behavior of the fungus is essential for developing effective disease management strategies, screening resistant maize genotypes, and improving integrated disease management practices. The findings of this study provide valuable baseline information for future epidemiological and host–pathogen interaction studies involving R. zeae in maize cultivation systems.