Epidemiology, Diversity, Physiology, and Chemical Management of Rhizoctonia solani Causing Web Blight in Country Bean

Country bean (Lablab purpureus L.) is an economically significant legume vegetable in Bangladesh, but its production is threatened by a new disease, web blight caused by Rhizoctonia solani. This study presented a comprehensive analysis of the pathogen's epidemiology, genetic diversity, physiology, host resistance, and chemical control strategies. Field surveys in six upazilas of Gazipur district revealed high disease prevalence (50%-80%), with incidence and severity ranging from 59%-92% to 38%-52%, respectively, peaking in October-November. Thirty isolates of R. solani were collected, and molecular characterization of four representative isolates identified AG-1 IA, AG-1 ID, and AG-5, indicating preliminary genetic variability among representative isolates. The detection of AG-1 ID and AG-5 is the first report on country bean. Optimal fungal growth occurred at 25°C-30°C and pH 7.0-9.0, with peptone, L-arginine, sodium nitrate, sorbitol, mannitol, and galactose as preferred nutrient sources. Maximum virulence, as measured by disease incidence, severity, and lesion development, was observed at 30°C. The pathogen exhibited a broad host range, infecting crops across Fabaceae, Poaceae, and Solanaceae. Screening of 94 country bean genotypes revealed a general lack of resistance, with most exhibiting moderate to high susceptibility. Among tested fungicides, Autostin 50 WG (carbendazim) and Nativo 75 WG (tebuconazole + trifloxystrobin) showed complete inhibition of mycelial growth in vitro. In planta application significantly reduced disease severity, achieving 83%-85% protection in preventive and 77%-81% in curative treatments, with efficacy lasting up to 15 days. These findings offer a novel insight into the web blight pathosystem in country bean, supporting the development of effective disease management strategies.