Influence of single and combined mixtures of metal oxide nanoparticles on eggplant growth, yield, and Verticillium wilt severity.

Verticillium wilt, caused by Verticillium dahliae, is one of the major diseases of eggplants. Nanoparticles (NP) of CuO, Mn2O3, and/or ZnO were sprayed alone onto leaves young eggplants and in different combinations and rates and then seedlings were transplanted into soil infested with V. dahliae in the greenhouse and field during 2015-2018. All combinations of NP were consistently less effective than CuO NP applied alone at 500 µg/ml at enhancing disease suppression, biomass, and fruit yield. CuO NP were associated with an increase in fruit yield (17% and 33% increase) and disease suppression (28% and 22% reduction) in 2016 and 2017, respectively, when compared to untreated controls. However, this effect was negated in the greenhouse and field experiments when CuO NP was combined with Mn2O3. Combining NP of CuO with ZnO resulted in variable effects; amendments increased growth and suppressed disease in greenhouse experiments, but results were mixed in the field. Leaf tissue analyses from the greenhouse experiments showed that Cu concentration in leaves was reduced when CuO NP was combined with other NPs even when application rates were the same amount. A simple competition for entry sites may explain why combinations of CuO NP and Mn2O3NP reduced efficacy but does not explain the lack of inhibition between Cu and Zn. NPs of CuO performed better than their larger bulk equivalent and studies on application rate found 500 µg/ml was optimal. No phytotoxicity, as determined, by leaf burning, necrotic spots or dead apical buds was noted even at the highest combined rates of 1,500 µg/ml.