Bacillus subtilis ED24 Controls Fusarium culmorum in Wheat Through Bioactive Metabolite Secretion and Modulation of Rhizosphere Microbiome.

Fusarium culmorum is a soil-borne fungal pathogen causing root and stem rot, seedling blight, and significant yield losses in small grain cereals, including wheat. This study aimed to evaluate the antifungal potential of Bacillus subtilis ED24, an endophytic strain isolated from Ziziphus lotus (L.) roots, and its effects on wheat growth and yield under controlled conditions. In vitro assays demonstrated that B. subtilis ED24 inhibited F. culmorum mycelial growth by up to 87%, associated with the secretion of 37 distinct secondary metabolites, predominantly involved in carbon cycling. In pot experiments, B. subtilis ED24 significantly enhanced wheat germination (85%) and growth compared to infected plants treated with the chemical fungicide tebuconazole. Although nutrient analysis showed significantly higher shoot nitrogen (32.34 mg/pot) and phosphorus (2.41 mg/pot) contents in the B. subtilis ED24 treatment compared to tebuconazole (8.11 and 0.18 mg/pot, respectively), no significant differences were observed when compared to the infected control (C-). Similarly, B. subtilis ED24 led to improved thousand grain weight (40.4 g), protein content (19.98%), and ash content (1.95%) relative to tebuconazole (29.1 g, 18.31%, and 1.74%, respectively), yet these values did not differ significantly from the infected control (C-). Notably, the number of seeds per pot was significantly increased by B. subtilis ED24 compared to the infected control (C-) (113.8 seeds/pot vs. 54.2 seeds/pot). Additionally, B. subtilis ED24 modulated the wheat rhizosphere microbiome, enriching beneficial taxa such as Eurotiomycetes fungal class and the bacterial genus Paramesorhizobium. These findings suggest that the antifungal activity and growth-promoting effects of B. subtilis ED24 are likely mediated through the synthesis of unique bioactive metabolites and microbiome modulation, offering a promising sustainable alternative to chemical fungicides in wheat production.