Foliar application of nano-zinc oxide crystals improved zinc biofortification in cauliflower (Brassica oleracea L. var. botrytis)

Lower levels of zinc in the food lead to Zn deficiency in the local population of Pakistan. The study aimed to increase the Zn fraction of an edible vegetable for which in-house fabrication of nano-Zn oxide crystals was performed using the sol-gel method. The synthesized nano-crystals exhibited similar to 25 nm diameter, and the XRD peaks indicated a single-phase hexagonal wurtzite crystal structure. The FT-IR spectrum confirmed the vibrational band of nZnO metallic crystals at a peak ranging between 400 and 500 cm(-1) and a lambda(max) at 380 nm, confirmed by UV-Vis spectra and SEM study, revealed an irregular morphology. These nanoparticles were applied as a foliar spray to 50-day-old cauliflower at 0, 25, 50, 75, and 100 mu M nZnO concentrations during a field experiment, and data were collected after 50 d of spray treatments at maturity (100-day-old plants). Cauliflower growth traits were improved and non-toxic effects on the foliage was recorded. An increase in leaf chlorophyll and free amino acids was recorded as well. Furthermore, ZnO nano-crystal foliar application caused improvements in curd diameter and curd weight resulting in higher productivity. Nano-Zn spray treatments after the curd initiation improved curd Zn fraction at, particularly at 100 mu M concentration (up to 34 mu g g(-1) DW). Conclusively, the applied nZnO crystals were non-toxic and biocompatible, and a significant fraction of Zn translocated to the cauliflower curd suggested the potential use in biofortification.