Estimating Efficacy of Indigenous Isolates of Three Trichoderma Species as Biocontrol Agents Against Alternaria alternata and Curvularia spicifera

Tomato is susceptible to various fungal pathogens, including Alternaria alternata and Curvularia spicifera, which can cause extensive post-harvest losses. Chemical fungicides have limited effectiveness in controlling post-harvest fungal pathogens and pose risk to human health and the environment. Therefore, this study assessed indigenous isolates of three species of Trichoderma (Tr1: T. longibrachiatum; Tr2: T. harzianum; and Tr3: T. asperellum) as biocontrol agents against two fungal pathogens in vitro and in vivo and determined their physicochemical analysis and plant-growth-promoting traits. The three species of Trichoderma exhibited catalase production in vitro, while T. longibrachiatum and T. asperellum showed the highest potential for plant-growth promotion by producing indole-3-acetic acid and phosphate solubilization but not nitrogen-fixing capability. T. harzianum showed lower potential in these traits. Mycelial growth was found to be maximum (5.77–12.27 cm) at 30 °C and a pH of 7–9, but inhibition (2.60–5.13 cm) was recorded at the highest temperature (45 °C) and pH (11). In vivo, studies on tomato fruits indicated that T. longibrachiatum and T. asperellum significantly (p < 0.05) reduced lesion diameters of A. alternata by 53.60% and 48.71%, respectively, and C. spicifera by 55.58% and 56.19%, respectively, relative to the infected control. Besides their antifungal efficacy, the three species of Trichoderma enhanced tomato seedling growth, particularly at 1/10 filtrate dilution, and improved fruit quality parameters by increasing firmness and nitrate content, while reducing oxidative stress. Physicochemical analysis indicated that Trichoderma-treated fruits had better firmness, pH, and nitrate value coupled with a reduction in oxidative stress (reduced malondialdehyde content) compared to pathogen-infected controls. The indigenous isolates of the three species of Trichoderma provided high efficacy as biocontrol agents of the two fungal pathogens that cause post-harvest losses of tomato, suggesting that biological control can replace synthetic chemicals in preserving tomato under storage conditions and contribute to agricultural sustainability.