https://doi.org/10.37229/fsa.fjas.2026.09.25

Common bean (Phaseolus vulgaris L.) is considered a very common vegetable crop in many countries worldwide. It is the world's most widely consumed food legume, providing an essential global source of dietary protein, complex carbohydrates and micronutrients. Damping-off caused by Rhizoctonia solani is a major constraint to common bean production, highlighting the need for effective and environmentally compatible disease management strategies. This study evaluated the antagonistic activity and biocontrol efficacy of three Trichoderma isolates and three Bacillus isolates against R. solani under laboratory, greenhouse, and field conditions. Three R. solani isolates were obtained from diseased bean roots collected from El-Fayoum, El-Sharkia, and El-Giza governorates and evaluated for pathogenicity on three common bean cultivars. The antagonistic activity of the bioagents was assessed using a dual-culture assay, followed by greenhouse evaluation of individual and combined treatments applied as powder and suspension formulations at different rates (2.5, 5, and 10 ml or g/kg seeds). The most effective treatments were subsequently evaluated under field conditions. All bioagents (Trichoderma harzianum T2, T. koningii T1, T. asperellum T3, Bacillus subtilis B2, B. velezensis B1, and B. subtilis B3) significantly inhibited the mycelial growth of the three R. solani isolates in vitro, with T. harzianum (T2) showing the highest inhibition. Paulista exhibited the highest pre-emergence damping-off and was therefore selected for subsequent experiments. Increasing application rates generally improved disease suppression, while suspension formulations generally provided greater protection than powder formulations. Among the tested treatments, the combined application of B. subtilis (B2) and T. harzianum (T2) provided the greatest reduction in damping-off and the highest plant survival in greenhouse and field experiments. Under field conditions, this combination achieved 90.7±2 % plant survival when applied as a suspension formulation compared with 26.7±3 % in the untreated control, restricted pre-emergence damping-off to 9.3±1%, and entirely suppressed post-emergence incidence (0.0±0 %). It also produced the highest shoot and root biomass, pod production, yield, and several biochemical parameters (total phenol content 15.4 mg/g, total chlorophyll 16.7 mg/g, soluble proteins levels 7.9 mg/g, resulting in a maximum yield 3.93±0.02 ton/fed compared to 1.71±0.09 ton/fed in the untreated control). These findings indicate that selected combinations of Trichoderma and Bacillus, particularly B2 + T2, have considerable potential and highly effective biological for integrated management strategy of R. solani-induced damping-off in common bean.