Biological Control of Sclerotinia sclerotiorum by Bacillus velezensis in Sunflower Under Field Conditions

Abstract

Field evaluation of Bacillus velezensis was conducted to assess its efficacy in the biological control of Sclerotinia sclerotiorum, the causal agent of stem rot in sunflower (Helianthus annuus L.), under natural field conditions. Treatments included soil application and foliar spray of bacterial formulations compared with untreated control plots. Disease incidence, disease severity index, plant growth parameters, and yield attributes were recorded throughout the cropping season. Results demonstrated a significant reduction in stem rot incidence in B. velezensis-treated plots compared to untreated controls, accompanied by improved plant vigor and higher yield performance. The biocontrol agent effectively colonized the rhizosphere and phyllosphere, exhibiting antagonistic activity against S. sclerotiorum through multiple mechanisms including antibiosis, competition for nutrients and space, and production of hydrolytic enzymes that degraded fungal hyphae and sclerotia. Field observations indicated reduced sclerotial germination and decreased infection pressure in treated plots, contributing to overall disease suppression. Environmental factors such as moderate soil moisture and temperature favored bacterial establishment and enhanced biocontrol efficacy. Yield analysis showed a corresponding increase in seed weight and head diameter in treated plots, reflecting improved crop health. The study highlights the potential of B. velezensis as an effective and environmentally safe alternative to chemical fungicides for managing stem rot in sunflower. Integration of this biocontrol agent into integrated disease management programs can enhance sustainable sunflower production by reducing pathogen load and minimizing reliance on synthetic fungicides. Further large-scale validation across diverse agro-climatic regions is recommended.