Integration of microbiological and molecular approaches in phytopathogen management to enhance disease resistance and agrobiological traits of vegetable crops

Background: Modern food production is increasingly focused on developing functional food products with pronounced biologically active properties. Tomatoes (Solanum lycopersicum L.) and sweet peppers (Capsicum annuum L.) are valuable vegetable crops rich in vitamins, antioxidants, and other phytonutrients. However, they are susceptible to fungal diseases, especially under greenhouse conditions. Objective: To study the effectiveness of microbiological complexes based on Bacillus subtilis and Trichoderma viride as plant growth stimulators and biological control agents for tomatoes and sweet peppers. Methods: The study was conducted in a greenhouse at the Scientific Centre of Vegetable and Industrial Crops, Ministry of Economy of the Republic of Armenia, during the spring and summer-autumn seasons of 2024–2025. Microbiological complexes based on B. subtilis and T. viride were applied to the soil via root treatment, both individually and in combination. Phenological parameters, yield, and biochemical characteristics of the fruits were assessed: the contents of ascorbic acid, total phenolic compounds, carotenoids, and sugars were measured spectrophotometrically; dry matter content- refractometrically; and nitrate levels- calorimetrically. A phytosanitary evaluation of the plants was also performed. The pathogens Fusarium oxysporum and Verticillium dahliae were identified using qPCR, followed by determination of the infection rate. Data were analyzed using ANOVA and the LSD test. Results: The conducted research demonstrated that the application of microbiological formulations had a positive effect on all stages of ontogenesis in tomato and sweet pepper, especially when B. subtilis and T. viride were used in combination, compared to both the control and the individual treatments. The formulations contributed to the acceleration of phenological phases, an extended fruiting period, and an increase in overall yield. Biochemical analysis of the fruits showed an increase in the content of vitamin C, total phenolic compounds, and carotenoids, indicating enhanced antioxidant capacity, as well as higher levels of sugars and dry matter. A reduction in nitrate content was also recorded, confirming an improvement in both nutritional and environmental value of the produce. Phytosanitary monitoring revealed a consistent decrease in the incidence of Fusarium wilt (F. oxysporum) and Verticillium wilt (V. dahliae). The formulations exhibited pronounced antagonistic activity against phytopathogens, particularly under combined application. Moreover, a cumulative effect observed in the second year of use resulted in further reduction of diseased plants, underscoring the formulations' potential as effective tools for long-term biological protection. Novelty: For the first time in Armenia, a comprehensive study was conducted on the synergistic action of microbial complexes based on PGPR (Bacillus spp.) and PGPF (Trichoderma spp.) when applied together on tomato and sweet pepper. A strong bioprotective and growth-stimulating effect was established, accompanied by improvements in agrobiological and biochemical characteristics. The results lay the groundwork for the implementation of environmentally safe bioprotection strategies in greenhouse vegetable production in Armenia and neighboring regions. Conclusion: Microbiological complexes based on Bacillus subtilis and Trichoderma viride are effective plant growth biostimulants and bioprotective agents, contributing to the production of environmentally friendly and functionally enriched tomatoes and peppers, making them promising for sustainable agriculture. Keywords: Bacillus subtilis, Trichoderma viride, biostimulants, tomato, sweet pepper, microbial complex, phytosanitary status, crop yield, antioxidant compounds, fruit quality