Foliar applied nanoscale and microscale CeO2 and CuO alter cucumber (Cucumis sativus) fruit quality

There is lack of information about the effects of foliar applied nanoparticles on fruit quality. In this study, three week-old soil grown cucumber seedlings were foliar-exposed to nCeO2, nCuO, and corresponding bulk counterparts at 50, 100, and 200mg/L. Respective suspensions/solutions were sprayed to experimental units in a volume of 250ml. Net photosynthesis rate (Pn), stomatal conductance (Gs), and transpiration rate (E) were measured 15days after treatment application and in 74day-old plants. Yield, fruit characteristics (size, weight, and firmness), Ce, Cu, and nutritional elements were also measured. Results showed a nano-specific decrement on Pn (22% and 30%) and E (11% and 17%) in seedling leaves exposed to nCeO2 and nCuO at 200mg/L, respectively, compared with control. nCeO2 at 50mg/L, bCeO2 at 200mg/L, and all Cu treatments, except nCuO at 100mg/L, significantly reduced fruit firmness (p≤0.05), compared with control. However, nCuO at 200mg/L and bCuO at 50mg/L significantly increased fruit fresh weight (p≤0.05). At 200mg/L, nCeO2 and bCeO2 reduced fruit Zn by 25%, while nCuO and bCuO reduced fruit Mo by 51% and 44%, respectively, compared with control. This study has shown that when the route of exposure is the foliage, differences in particle size are less significant, compared to root-based exposure. To the authors' knowledge, this is the first report on the effect of foliar application of nCeO2 and nCuO upon yield and nutritional quality of cucumber.