Biostimulant effects of biogenic ZnO nanoparticles on in vitro explants proliferation of olive cultivar ‘Moraiolo’

Nowadays, there is a growing interest in nanotechnology, which refers to technologies, processes, and techniques which involve the production and use of materials of nanometric dimensions, the so-called nanoproducts or nanoparticles. The present work aimed to evaluate the effect of biogenic zinc oxide nanoparticles (ZnO-NPs) obtained from an extract of Lemna minor L. on the in vitro proliferation phase of olive tree (‘Moraiolo’) explants. Unlike chemical ones, the green synthesis of ZnO-NPs process does not impact the environment. Three different concentrations (2, 6, and 18 mg L-1) of the biogenic ZnO-NPs were added to the olive medium (OM), and the effect on the explants was compared with those recorded in samples grown in medium without the NPs. Forty-five days after the treatments, the percentage of viability, shoots number and length, the number of nodes, green and callus fresh weight, total dry weight, chlorophylls and soluble protein contents were measured in the proliferated explants. In the olive explants grown in substrates containing ZnO-NPs, a higher number of shoots and nodes, fresh green weight, and total dry weight were found than in control samples. The observed effects on explants growth can be due, at least partly, to the higher chlorophylls and soluble protein content promoted by the addition of ZnO-NPs to the growth medium. In conclusion, the biogenic ZnO-NPs showed a stimulatory effect on the in vitro proliferation of explants, revealing the possibility of using this nanostructured material for improving olive micropropagation. In particular, the beneficial effects found are of great interest as ZnO-NPs positively affected the in vivo acclimatization phase of the vitro-derived plantlets.