Preventive Versus Curative Application of Endophytic Trichoderma harzianum and Bacillus subtilis for Biological Control of Meloidogyne javanica and M. incognita in Olive Under Greenhouse Conditions

Root-knot nematodes (Meloidogyne javanica and M. incognita) constrain olive (Olea europaea L.) production and require safer alternatives to chemical nematicides. Despite the growing interest in microbial biocontrol agents, limited information is available on how application timing and microbial consortia influence nematode suppression and host biochemical responses in olive. This greenhouse study evaluated endophytic Trichoderma (T. harzianum) and Bacillus (B. subtilis), applied alone or in combination, either before or after nematode inoculation, to determine how biocontrol treatment timing influences nematode suppression, plant performance, and host biochemical responses. Across both nematode species, preventive application consistently outperformed curative application, and the combined treatment delivered the strongest overall protection. Preventive co-application reduced nematode infection, improved root and shoot growth, attenuated oxidative damage, and preserved chlorophyll more effectively than single-agent or post-inoculation treatments. Spectroscopic (Fourier Transform Infrared (FTIR)) and multivariate analyses further showed that effective treatments were associated with lower nematode-associated protein and lipid signals and stronger signatures of structural defense in root tissues. Although M. javanica caused greater physiological disruption than M. incognita, both species responded to the same general treatment pattern. These findings show that early establishment of microbial biocontrol agents is critical for durable suppression of root-knot nematodes in olive and supports preventive microbial consortia as a promising strategy for integrated nematode management.