Enhancing tomato immunity against root-knot nematodes using PGPF and Melithorin® through biochemical and molecular approaches

Abstract

This article focused on assessing the biocontrol effectiveness of four plant growth-promoting fungal (PGPF) species—Verticillium lecanii, Penicillium buchwaldii, Alternaria photistica, and Aspergillus niger—alongside the commercial formulation Melithorin®(fosthiazate 90 %), against the root-knot nematode Meloidogyne incognita in tomato plants. Laboratory bioassays demonstrated that Melithorin® had the most potent nematocidal effect, causing 94 % juvenile mortality after 96 h. Among the fungal isolates, A. niger showed the highest activity (92.6 %). Under greenhouse conditions, Melithorin® significantly reduced root gall formation and juvenile nematode populations by 96.6 % and 84.9 %, respectively. The fungal treatments also exhibited suppressive effects, with V. lecanii and A. niger performing better than P. buchwaldii and A. photistica. Chemical analysis using gaschromatography–mass spectrometry (GC-MS) revealed the presence of several bioactive metabolites in ethyl acetate extracts of the fungal isolates. Noteworthy compounds included 1H-benzotriazole, 5-nitro in V. lecanii; desulphosinigrin in P. buchwaldii; and a shared phenolic compound—2,2′-methylenebis[6-(1,1-dimethylethyl)-4-methylphenol]—in both A. photistica and A. niger. These metabolites are likely contributors to the observed nematocidal activity. Biochemical assessments of the treated tomato plants indicated that nematode infestation triggered oxidative stress, as reflected by elevated malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) levels. Applications of PGPF and Melithorin® alleviated this stress by significantly lowering MDA and H₂O₂ content, while enhancing total phenolics and the activities of peroxidase (POD) and polyphenol oxidase (PPO) enzymes.

Furthermore, isozyme profiling revealed increased expression of PPO isoforms, particularly PPO2, PPO3, and PPO4, with the highest intensities observed in plants treated with Melithorin®.In summary, Melithorin® proved to be the most effective agent in reducing nematode damage and activating plant defense responses. PGPF showed promising potential, both in suppressing nematodes and enhancing the plant's biochemical resistance mechanisms.