Using Trichoderma harzianum to stimulate defensive enzymes in tomato plants infected with Alternaria solani, which causes early blight disease, in vivo and in vitro

A pot experiment for the 2024–2025 agricultural season was conducted using a completely randomized design to evaluate the effectiveness of Trichoderma harzianum in the biological control of Alternaria solani, the cause of early blight on tomato plants, in vivo and in vitro. The bioactivity of the 15-day culture filtrate extracted from T. harzianum was assessed against pathogenic A. solani fungi. The dual culture assay (DCA) was calculated to evaluate the efficacy of T. harzianum on the pathogenic fungus in vitro. Chitinase and 𝛽-glucanase enzymes in T. harzianum were measured to determine their role in fungal cell degradation. To understand the role of T. harzianum filtrate in stimulating defensive enzymes in plants (in vivo), the activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), and catalase (CAT) were measured in tomato plants after treatment with T. harzianum filtrate. The results showed that, in the dual culture assay, the largest mean diameter of Trichoderma was (80.00 ± 0.71) in 7 days (168 hr), while A. solani showed the largest diameter (25.00±0.71) in 4 days and then decreased to the lowest diameter (10.20±0.66) in 7 days. The age of Trichoderma filtrate and the incubation period had significant differences (𝑃 ≤ 0.05) in A. solani colonies. The 15-day extracts of T. harzianum had significant cytotoxic effects toward A. solani. The results of chitinase and 𝛽-glucanase enzymes extracted from the culture medium of T. harzianum showed 2.87 and 1.68 Units/mL, respectively, compared with the control (non-Trichoderma cultured medium), which gave 0.021 and 0.013 Units/mL, respectively. The results also showed that the defensive enzymes in tomato plants (PAL, PPO, POD, and CAT) showed higher levels in plants treated with Trichoderma filtrate than in untreated plants, further supporting the role of Trichoderma filtrate in stimulating plant resistance. In vitro findings using several methodologies indicate that T. harzianum was the most effective in suppressing A. solani growth. It may serve as a possible biocontrol agent in the future.