European Journal of Sustainable Agroecosystems

Background: Early blight caused by Alternaria solani is one of the major constraints to global tomato production with severe economic losses in favorable climates. Chemical fungicides can control diseases but raise concerns for the environment and the development of resistance to the pathogen. Biological control agents and organic amendments are sustainable alternatives for disease management.
Objective: This study investigated the efficacy of Bacillus subtilis and compost tea, either alone or in combination, in suppressing Alternaria solani and improving tomato plant growth, physiological performance and yield under field conditions.
Methods: Tomato plants (cv. ‘Roma VF’) were grown under field conditions and treated with Bacillus subtilis inoculum, compost tea, combined Bacillus subtilis + compost tea, chemical fungicide (mancozeb; standard comparison) and untreated control. Treatments were applied at 7 day intervals during the growing season. Early blight disease incidence and severity were recorded fortnightly. Plant growth parameters, physiological traits, defense enzyme activities, soil microbial properties and fruit yield were estimated.
Results: Bacillus subtilis alone and compost tea alone reduced the disease severity by 56.2 and 48.7%, respectively. The combined treatment of Bacillus subtilis + compost tea showed a synergistic effect, with 72.3% reduction in disease severity and disease suppression similar to chemical fungicide (mancozeb; 78.1% reduction). Biological treatments significantly increased plant height (15–22% over control), stem diameter, leaf chlorophyll content and photosynthetic efficiency. The activities of antioxidant enzymes (SOD, CAT, POD) and defense enzymes (PAL, β-1,3-glucanase) were significantly increased in treated plants. Combined treatments increased the soil microbial biomass carbon and respiration rate by 3.4 fold. Marketable fruit yield increased from 32.4 t·ha−1 (control) to 48.6 t·ha−1 (combined treatment) with 50% productivity gain. Application of compost tea enhanced soil microbial communities and nutrient bioavailability.
Conclusions: Integrated application of Bacillus subtilis and compost tea for effective biological suppression of Alternaria solani in tomato An integrated approach reduces reliance on chemical fungicides and improves plant health and production. Mechanistic evidence indicates dual suppression via direct microbial antagonism and induced systemic resistance activation. The use of this biological management strategy is conducive to environmentally sustainable tomato production systems.