Eco-Friendly Chitosan–Jojoba Soil Amendments Improve Growth and Resilience of Cucumber and Suppress Root-Knot Nematodes Under Greenhouse Conditions

Root-knot nematodes (Meloidogyne incognita) are among the most destructive pests affecting cucumber production, causing significant reductions in plant growth and yield. This study investigated the efficacy of chitosan-based soil amendments, alone and in combination with hot or cold jojoba (Simmondsia chinensis) leaf extracts and leaf powder, in suppressing nematode infestation and enhancing cucumber vegetative growth under greenhouse conditions. Treatments were evaluated for their impact on nematode reproduction, including egg masses, eggs per egg mass, second-stage juveniles (J2s), female numbers, and gall formation, as well as on plant growth parameters such as height, leaf number, and fresh and dry biomass. Chitosan alone reduced egg masses, eggs per egg mass, and J2s by 43.83%, 56.35%, and 50.63%, respectively, while hot water extract reduced them by 44.10%, 54.18%, and 50.48%. Cold extract was less effective, with reductions of 31.36%, 48.29%, and 40.31%, whereas leaf powder alone caused reductions of 44.20%, 54.60%, and 45.00%. Combined applications exhibited higher efficacy: hot extract + chitosan reduced egg masses, eggs per egg mass, and J2s by 61.64%, 59.45%, and 55.57%, leaf powder + chitosan by 64.38%, 60.70%, and 60.71%, and the triple treatment (leaf powder + chitosan + hot extract) achieved the highest suppression, reducing egg masses, eggs per egg mass, and J2s by 75.90%, 74.66%, and 69.22%, respectively. All treatments significantly enhanced cucumber growth compared with the naturally infested control. The triple treatment increased plant height by 38.5%, leaf number by 42.1%, fresh shoot biomass by 46.3%, and dry shoot biomass by 44.8%. Single treatments also improved growth, though to a lesser extent, reflecting a synergistic effect of chitosan and jojoba-derived amendments. These findings demonstrate that integrating biopolymer-based amendments with plant-derived bioactive compounds can simultaneously suppress root-knot nematode populations and promote cucumber growth. This study provides a solid basis for developing sustainable and eco-friendly integrated pest management strategies that reduce reliance on chemical nematicides.