Potential Biocontrol Activity of Brevibacillus brevis against Damping-Off and Root Rot Diseases in Sunflower (Helianthus annuus)

Abstract

Root-rot and damping-off diseases pose significant challenges to sunflower cultivation, particularly in newly reclaimed and arid regions. This study aimed to isolate and evaluate native endophytic bacteria from sunflower plants for their biocontrol potential against major soilborne pathogens and their ability to enhance plant growth. A total of 25 endophytic bacterial isolates were recovered from healthy sunflower leaves, of which five strains Bacillus cereus, Bacillus sp., B. pseudomycoides, B. paramycoides, and Brevibacillus brevis were selected based on their consistent antagonistic activity against Rhizoctonia solani, Fusarium solani, F. oxysporum, and Macrophomina phaseolina. In vitro assays confirmed that the selected isolates effectively inhibited fungal growth through multiple
mechanisms, including secretion of antifungal metabolites, production of volatile compounds, and enzymatic activity. In greenhouse and field experiments conducted over two consecutive seasons 2022 and 2023, individual and mixed applications of these bacteria significantly reduced disease incidence and severity. Notably, a mixed formulation applied as a soil drench led to a reduction in disease severity by up to 36.3% and markedly improved plant biomass parameters. Beyond disease suppression, the bacterial treatments also promoted plant growth, with measurable increases in shoot and root length and weight, particularly under combined stress conditions. These effects are likely mediated through production of phytohormones, siderophores, and enhanced nutrient uptake. The integration of these endophytic strains into a bioformulation represents a promising approach for sustainable sunflower production in challenging environments. These results represent a continuation of research efforts to evaluate biological control agents for disease management, thereby contributing to the search for safe alternatives that help reduce reliance on chemical pesticides.