Amelioration of the growth and physiological responses of Capsicum annum L. via quantum dot-graphene oxide, cerium oxide, and titanium oxide nanoparticles foliar application under salinity stress

Salinity is one of the predominant abiotic stressors that reduce plant growth, yield, and productivity. Ameliorating salt tolerance through nanotechnology is an efficient and reliable methodology for enhancing agricultural crops yield and quality. Nanoparticles enhance plant tolerance to salinity stress by facilitating reactive oxygen species detoxification and by reducing the ionic and osmotic stress effects on plants. This experiment was conducted to study the effects of NaCl salinity stress (0, 100, and 200 mM), and foliar application of quantum dot-graphene oxide, nano-TiO₂, and CeO₂ (zero and 2 g/l) on the growth and physiological responses of Capsicum annum L. The results revealed that the interaction effects of treatments significantly affected plant and fruit fresh weight, chlorophyll a, total soluble solids, phenolics, malondialdehyde, H₂O_2, and proline content. Moreover, catalase activity and sodium, and phosphorus content were responded to the treatments. The highest fresh weight of plants and fruits, fruit diameter, and chlorophyll a content were recorded under no-salinity × quantum dot-graphene oxide foliar use. The highest data for total phenolics content was recorded at NaCl_{100 mM} × quantum dot-graphene oxide. In contrast, the maximum flavonoids content belonged to NaCl_{100 mM} × quantum dot-graphene oxide and NaCl_{100 mM} × TiO₂. The experimental treatments independently affected the number of fruits, chlorophyll b, carotenoids, and vitamin C content, as well as K/Na ratio. The foliar treatment of quantum dot-graphene oxide nanoparticles improved the carotenoids and vitamin C content, stem diameter, and fruit number. The overall results disclosed that, when plants were exposed to high salinity levels; the foliar treatments were unable to effectively mitigate the negative impacts of salt stress on the plant, except for certain traits such as total phenolics, flavonoids, and TSS levels. However, under the low and mild salinity depression, the foliar treatments were enough capable to overcome the salinity defects.