Biological Control of Rhizoctonia solani by Coniothyrium minitans in Lettuce Under Field Conditions

Abstract

Field evaluation of the mycoparasitic fungus Coniothyrium minitans was conducted to assess its effectiveness in suppressing Rhizoctonia solani, the causal agent of damping-off and bottom rot in lettuce (Lactuca sativa L.) under natural field conditions. Experimental plots were established with uniform disease pressure, and treatments included soil application and seedling drenching with C. minitans formulations compared with untreated controls. Disease incidence, severity index, plant survival rate, and yield parameters were recorded throughout the cropping period. Results demonstrated a significant reduction in R. solani infection in treated plots, with improved seedling establishment and reduced pre- and post-emergence damping-off. The biocontrol agent established effectively in the rhizosphere, exhibiting antagonistic activity through parasitism of sclerotia, competition for nutrients, and secretion of lytic enzymes. Microscopic observations confirmed degradation of sclerotial structures of R. solani in treated soils, indicating active mycoparasitism. Yield analysis showed a corresponding increase in marketable lettuce heads in plots receiving C. minitans compared to untreated controls. Disease suppression efficacy was influenced by soil moisture and organic matter content, with enhanced performance observed under moderately moist soil conditions. The findings highlight the potential of C. minitans as a sustainable biological control agent for managing soil-borne diseases in leafy vegetable production systems. Integration of this biocontrol strategy into existing integrated disease management programs can reduce reliance on chemical fungicides and support environmentally sustainable lettuce cultivation. Further large-scale multi-location trials are recommended to optimize application timing, dosage, and formulation stability under diverse agro-climatic conditions.