Management of Root Rot (Rhizoctonia solani Kühn) of Common Bean Using Host Resistance and Consortia of Chemicals and Biocontrol Agents.

Abstract

Rhizoctonia root rot and web blight caused by Rhizoctonia solani Kühn is one of the destructive diseases of the common bean (Phaseolus vulgaris L.). A two-year study was conducted (2019-2021) to evaluate the common bean landraces and genotype, biocontrol agents, and chemical fungicides against the pathogen. Nine landraces from high-altitude agriculture in the Jumla district in western Nepal (29.27443900, 82.19332200; 2540 m msl) and one genotype of commercial common bean from the sub-tropical Chitwan district in central Nepal (27.65186564, 84.34869288; 256 m masl) were evaluated for resistance against the pathogen under screenhouse and field conditions. All were found highly susceptible to the pathogen and the highest lesion length (3.02 cm) was measured in the Rato Male Simi followed by Rato Sano Chhirke Simi (2.40 cm) in Chitwan conditions. Three chemical fungicides-SAAF™ (carbendazim 12% + mancozeb 63% WP), Vitavax^® (carboxin 37.5% + thiram 37.5% DS), and Nativo^® (tebuconazole 50% + trifloxystrobin 25% w/w (75 WG)-and three biocontrol agents-Trichoderma viride (10⁹ cfu/mL), Pseudomonas fluorescens (10⁹ cfu/mL), and Bacillus subtilis (10⁸ cfu/mL)-were evaluated as seed and soil treatments in fourteen different combinations against R. solani. SAAF™ and Vitavax^® were found highly effective as they completely suppressed the incidence of pre-emergence damping off. SAAF™ was equally effective followed by Vitavax^® and Nativo^® in suppressing post-emergence damping off. On the other hand, the highest disease incidence (26.63%) was recorded in treatment where seed treatment with Pseudomonas fluorescens formulation at the rate of 10 g per kg of FYM slurry along with soil application with Pseudomonas fluorescens formulation at the rate of 10 kg per ha with 50 kg FYM was applied, whereas the lowest disease incidence (4.96%) occurred in SAAF™ for both seed and soil applications. Highest grain yield (4125 kg/ha) was recorded on Nativo^® where seed treatment at the rate of 1.5 g per kg along with soil drenching at the rate of 1.5 g per liter was used. Thus, it can be concluded that the best control for pre-emergence damping off was achieved by SAAF™ where seed treatment at the rate of 2 g per kg along with soil drenching at the rate of 2 g per liter and Vitavax^® as seed treatment at the rate of 2 g per kg along with soil drenching at the rate of 2 g per liter was used, while the best control of post-emergence damping off was achieved with combined seed treatment and soil treatment with SAAF™. There was no incidence of web blight throughout the growing period. Our findings could be useful in devising strategies for the integrated management of R. solani causing root rot disease in common beans.