Drought stress impairs plant growth leading to depression in yield. This experiment aimed to elucidate the substantial impact of silicon (Si) [in forms of SiO2 and SiO2-nanoparticles (SiO2-NPs)] on modulating adverse effects of drought stress on strawberry plants. The plants grown in the greenhouse were exposed to drought stress simulating 25% field capacity (FC) (severe stress), 50% FC (moderate stress), and 100% FC (control). The strawberry plants were then sprayed with suspensions containing SiO2 or SiO2-NPs (50 mg L−1). The SiO2 treatment improved morphological parameters (number of plant leaves and length of petiole). Under drought stress, application of foliar SiO2 and SiO2-NPs increased osmolytes such as proline and total soluble sugar and improved chlorophylls (Chl a, Chl b, and total Chl) and carotenoids (CARs) as well as Chl fluorescence in strawberry plants as compared to non-treated ones. Moreover, treatment by SiO2 raised tolerance to drought by promoting the activity of antioxidant enzymes such as peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX) and phenylalanine ammonia lyase (PAL) as well as reduced hydrogen peroxide (H2O2) and malondialdehyde (MDA) activity in strawberry plants. Drought stressed strawberry plants treated by Si exhibited the recovery in antioxidant activity and phenolic compounds as non-enzymatic antioxidants. The modifications of abscisic acid and phenolic compounds occurred following up-regulation of some responsive genes as a beneficiary response to drought stress when SiO2 and SiO2-NPs were applied. This application of SiO2 and SiO2-NPs can contribute to protect strawberry plants against damaging effects of drought stress.
