Biogenic ZnO Nanoparticles in Kiwifruit In Vitro Culture: Growth and Physiological Responses

Nanotechnology offers new opportunities to improve plant propagation in vitro. This research assessed how biogenic zinc oxide nanoparticles (ZnO-NPs) influenced the in vitro proliferation, rooting performance, and biochemical traits in kiwifruit (Actinidia deliciosa ‘Hayward’). Explants were grown for three successive proliferation subcultures on Quoirin and Lepoivre medium containing ZnO-NPs at 0, 2, 6, or 18 mg L−1, and then transferred to an auxin-enriched medium for rooting. Relative to the control, ZnO-NPs significantly raised both the number of shoots per explant and shoot fresh weight, while shoot length, total dry weight, and explant viability were unaffected. A marked increase in callus fresh weight was observed at the highest ZnO-NP concentration. Moreover, ZnO-NPs significantly increased the percentage of rooted plants, while root number and length were not influenced. Biochemical analyses revealed an inductive effect on the photosynthetic pigment accumulation, with total chlorophyll and carotenoids increasing in a dose-dependent manner. In addition, total flavonoid content was significantly enhanced at the two highest ZnO-NP concentrations, whereas phenols and soluble carbohydrates were not affected. Overall, these results show that biogenic ZnO-NPs can positively modulate both morphogenetic and metabolic responses in kiwifruit explants, highlighting their potential to improve micropropagation efficiency.