Indirect Effects of Zinc Oxide Nanoparticles and Grafting Technique on the Performance of the Two-Spotted Spider Mite Populations and the Growth of Greenhouse-Grown Cucumbers

Zinc oxide nanoparticles (ZnO-NPs) have garnered significant interest due to their role in enhancing seed germination, plant growth, seedling vigor, and crop pests’ management. The present study assessed the indirect effects of ZnO-NPs foliar application (as a supplementary nanofertilizer) and grafting technique on the suitability of cucumber plants for the two-spotted spider mite, Tetranychus urticae Koch (TSSM) and its natural predators in greenhouses. The effects on cucumber’s vegetative growth, biochemical parameters, and yield were also evaluated. The plant leaves were treated with ZnO-NPs at four concentrations: 0 (control), 100, 200, and 300 mg L-1 in three rounds. The efficacy of ZnO-NPs in suppressing the density of TSSM eggs and motile stages was dependent on concentration. The recent findings indicated that grafted plants subjected to 200 and 300 mg L-1 exhibited the lowest counts of TSSM eggs and motile stages in comparison to non-grafted plants. The application of ZnO-NPs also increased the population density of both phytoseiid predators Phytoseiulus persimilis A.-H and Neoseiulus cucumeris (Oudemans). Results also showed that the interaction between grafting and ZnO-NPs application significantly enhanced plant length, leaf dry matter, photosynthetic pigment content, and fruit yield. The leaf concentrations of macro- and micro-nutrients, along with biochemical leaf parameters, were markedly improved. These findings demonstrated the efficacy of ZnO-NPs and grafting technique as a combined treatment in suppressing TSSM density, augmenting the effectiveness of natural predators, and simultaneously improving cucumber growth and yield.