Effect of Methods Application of Copper Nanoparticles in the Growth of Avocado Plants

The aim of this greenhouse study was to evaluate root irrigation, foliar spray, and stem injection in order to find the best method for the nanofertilization of avocado plants with green synthesized CuNPs. One-year-old avocado plants were supplied four times (every 15 days) with 0.25 and 0.50 mg/ml of CuNPs through the three fertilization methods. Stem growth and new leaf formation were evaluated over time and after 60 days of CuNPs exposure, several plant traits (root growth, fresh and dry biomass, plant water content, cytotoxicity, photosynthetic pigments, and total Cu accumu-lation in plant tissues) were evaluated for CuNPs improvement. Regarding the control treatment, stem growth and new leaf appearance were increased by 25 % and 85 %, respectively, by the CuNPs supply methods of foliar spray>stem injection>root irrigation, with little significant differences among NPs concentrations. Avocado plants supplied with 0.25 and 0.50 mg/ml CuNPs maintained a hydric balance and cell viability ranged from 91 to 96 % through the three NPs application methods. TEM did not reveal any ultrastructural organelle changes induced by CuNPs in leaf tis-sues. The concentrations of CuNPs tested were not high enough to exert deleterious effects on the photosynthetic ma-chinery of avocado plants, but photosynthetic efficiency was also found to be improved. The foliar spray method showed improved uptake and translocation of CuNPs, with almost no loss of Cu. In general, the improvement in plant traits indicated that the foliar spray method was the best for nanofertilization of avocado plants with CuNPs.