Evaluation of pathogenic variation among Rhizoctonia solani isolates infecting different crops and potential biocontrol agents

Rhizoctonia solani is an important broad-spectrum fungal pathogen that infects over 200 plant species including tomato, melon, and watermelon. This study evaluated the pathogenicity of various R. solani isolates (Rs26, Rs94, Rs13, Rs57, and Rs123) and the efficacy of biological agents (Trichoderma harzianum, T. viride, Metarhizium sp., Gliocladium sp.) under laboratory and greenhouse conditions for eco-friendly disease management. The results of the pathogenicity assay confirmed the varying aggressiveness of the isolates, with Rs94 and Rs13 causing the most severe disease in watermelon (disease severity (DS) = 3.80 and 3.83, disease severity index (DSI) = 90.43% and 95.75%, respectively). Similarly, isolate Rs26 displayed the highest pathogenicity in tomatoes (DS = 3.84; DSI = 94.86%). Melon exhibited high susceptibility across all isolates, with consistently high DS and DSI values exceeding 2.59 and 80.97%, respectively. Subsequent in vitro and in vivo assays demonstrated the antifungal potential of all tested agents against R. solani isolates. Notably, Trichoderma spp. displayed the most consistent and significant inhibition (mycelial growth reduction 82.97%-94.67%), with T. harzianum demonstrating superior performance. Greenhouse trials confirmed the effectiveness of T. harzianum as a preventative treatment, enhancing plant enzyme activity [peroxidase = 4.97-5.29 units g-1 ml-1 min-1 for tomato and watermelon, respectively; catalase = 99.93-101.22 units g-1 ml-1 min-1 for watermelon and melon, respectively] and significantly reducing disease severity index (DSI < 12.43%). These findings highlight the potential of T. harzianum as a sustainable and eco-friendly strategy for managing R. solani damping-off disease in tomato, melon, and watermelon crops.