Background and Objectives
Meloidogyne spp. are among the most destructive plant-parasitic nematodes and cause substantial reductions in crop quality and productivity. Commonly known as root-knot nematodes (RKNs), Meloidogyne species are obligate endoparasites that infect a wide range of economically important crops. Among them, Meloidogyne incognita is one of the most damaging species and has been reported to cause yield losses of up to 27% in tomato (Lycopersicon esculentum) and up to 50% in vegetable crops worldwide. Root-knot nematode infection induces oxidative stress in host plants, activating defense mechanisms that limit cellular damage and help restore physiological balance. In response to nematode infection, plants undergo several biochemical and physiological changes, including alterations in photosynthetic pigments, phenolic compounds, osmoprotectants, and organic acids. Trichoderma species are well known for their antagonistic activity against plant-parasitic nematodes through mechanisms such as parasitism, competition, and the production of bioactive metabolites. In addition to their biocontrol activity, Trichoderma spp. can increase plant tolerance to biotic and abiotic stresses by stimulating the production of defense-related metabolites and activating plant defense pathways. These beneficial fungi may improve plant performance under nematode stress by increasing photosynthetic pigment levels and modifying the accumulation of phenolic compounds, osmoprotectants, and organic acids. Furthermore, Trichoderma spp. can induce systemic resistance, thereby strengthening plant defenses against a broad range of pathogens. The present study evaluated the effects of root-knot nematode infection on selected biochemical and physiological parameters in tomato plants and investigated the potential of Trichoderma atrobrunneum and Trichoderma brevicompactum to alleviate nematode-induced stress.
Materials and Methods
The experiment was conducted under greenhouse conditions at 24 ± 2 °C. Thirty-day-old tomato seedlings were transplanted into 1-kg pots containing a substrate of sand, sandy loam, and peat moss at a 2:1:1 ratio. Before use, the substrate was steam-sterilized in an autoclave at 121 °C and 15 psi for 30 min. At transplanting, each pot was inoculated with 20 mL of a fungal spore suspension containing 1 × 10⁸ conidia mL⁻¹ in sterile water. One week after inoculation with the biocontrol agents, each pot was inoculated with 2,000 nematode eggs and second-stage juveniles (J2s). Sixty days after nematode inoculation, plant samples were collected to determine several biochemical and physiological parameters, including chlorophyll, carotenoid, flavonoid, and phenolic contents; hydrogen peroxide (H₂O₂) content; and peroxidase (POD) and catalase (CAT) activities. Data were analyzed using SPSS software. Means were compared using Duncan’s multiple range test, with statistical significance set at P < 0.05.
Results
The physiological and biochemical responses of tomato plants pretreated with two Trichoderma isolates were evaluated. Chlorophyll and carotenoid contents, hydrogen peroxide (H₂O₂) levels, enzymatic antioxidant activities (catalase and peroxidase), and non-enzymatic antioxidant contents (phenolics and flavonoids) were assessed as indicators of plant responses to nematode-induced stress. Both Trichoderma isolates significantly improved the physiological and biochemical responses of nematode-infected plants. Compared with untreated infected plants, T. brevicompactum (LT134I) increased chlorophyll, carotenoid, phenolic, and flavonoid contents by 158%, 144.8%, 121.8%, and 200%, respectively, and increased catalase and peroxidase activities by 86% and 89%, respectively. H₂O₂ levels decreased by 38.5%. Similarly, T. atrobrunneum (LT6I) increased chlorophyll, carotenoid, phenolic, and flavonoid contents by 118%, 62%, 50.2%, and 91%, respectively, while catalase and peroxidase activities increased by 48% and 53.5%. H₂O₂ levels decreased by 20.7%. Across all evaluated parameters, T. brevicompactum showed greater effects than T. atrobrunneum. In contrast, nematode infection alone reduced chlorophyll and carotenoid contents by 58.7% and 42%, respectively, and decreased catalase and peroxidase activities by 19% and 17.8%. At the same time, H₂O₂, phenolic, and flavonoid levels increased by 51%, 29.5%, and 32%, respectively.
Discussion
These findings indicate that applying Trichoderma isolates can mitigate the physiological and biochemical stress associated with root-knot nematode infection in tomato plants. Both isolates strengthened antioxidant responses and increased protective metabolite accumulation, which may contribute to greater plant tolerance to nematode-induced stress. Among the tested isolates, T. brevicompactum was more effective in improving defense-related parameters and reducing oxidative damage, as reflected by lower H₂O₂ levels and higher antioxidant enzyme activities. These results suggest that T. brevicompactum may have particular potential as a biological control agent against root-knot nematodes in tomato. More broadly, using Trichoderma isolates may provide a cost-effective and environmentally sustainable approach to supporting plant health under nematode stress. However, further studies are needed to clarify the mechanisms underlying the interactions among Trichoderma, the host plant, and root-knot nematodes.