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

Abstract 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 n CeO 2 , n CuO, and corresponding bulk counterparts at 50, 100, and 200 mg/L. Respective suspensions/solutions were sprayed to experimental units in a volume of 250 ml. Net photosynthesis rate ( Pn ), stomatal conductance ( Gs ), and transpiration rate ( E ) were measured 15 days after treatment application and in 74 day-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 n CeO 2 and n CuO at 200 mg/L, respectively, compared with control. n CeO 2 at 50 mg/L, b CeO 2 at 200 mg/L, and all Cu treatments, except n CuO at 100 mg/L, significantly reduced fruit firmness ( p  ≤ 0.05), compared with control. However, n CuO at 200 mg/L and b CuO at 50 mg/L significantly increased fruit fresh weight ( p  ≤ 0.05). At 200 mg/L, n CeO 2 and b CeO 2 reduced fruit Zn by 25%, while n CuO and b CuO 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 n CeO 2 and n CuO upon yield and nutritional quality of cucumber.