Effect of Silicon Application Method on Morpho-Physio-Biochemical Traits of Cucumber Plants under Drought Stress

Drought, one of the most frequent natural disasters, is a devastating abiotic stress that arises unpredictably, develops gradually, and carries long-lasting repercussions even after it ceases. The duration and severity of drought markedly impact plant growth, development, and yield by disrupting normal morpho-physio-biochemical processes. Silicon (Si) is regarded as a crucial element for mitigating the detrimental effects of abiotic stress, including drought. The objective of this study was to evaluate the effect of Si application method on morpho-physio-biochemical traits of cucumber plants under drought stress. Two independent polyhouse experiments were conducted where cucumber (Cucumis sativus L.) plants were grown under four levels of soil moisture that included 40%, 60%, 80%, and 100% field capacity (FC) and Si was applied either in the form of seed priming (Experiment 1) or as soil drench (Experiment 2). For the seed priming study, four doses of Si (in the form of monosilicic acid with 20% Si content) applied were 0.25, 0.5, 1.0, and 2.0 mM along with a control in which seeds were sown directly without any priming. For the soil application study, four doses of Si (in the form of monosilicic acid with 20% Si content) applied were 15, 30, 60, and 120 kg ha^–1 along with a control. The minimal soil moisture level (40% FC) resulted in 55–68% and 53–76% reduction in root dry matter in Experiment 1 and Experiment 2, respectively, in comparison to that at 100% FC throughout Si doses. Fruit yield, irrigation water productivity, and net photosynthetic rate exhibited a respective reduction of 77–84% and 78–84%, 25–52% and 13–47%, and 37–46% and 26–33% in Experiment 1 and Experiment 2, respectively, at 40% FC than those at 100% FC throughout Si doses. The exogenous application of Si was equally efficient irrespective of application methods. Seed priming with 0.5 mM Si outperformed all other doses and resulted in an increase of 199–284%, 169–263%, and 20–59% in fruit yield, irrigation water productivity, and net photosynthetic rate, respectively, in comparison to the control throughout soil moisture levels. Among different soil application doses of Si, 60 kg ha^–1 was the most efficient, which resulted in 217–293%, 198–307%, and 11–33% enhancement in fruit yield, irrigation water productivity, and net photosynthetic rate, respectively, in comparison to the control throughout soil moisture levels. Exogenous incorporation of Si as seed priming at 0.5 mM and as soil drench at 60 kg ha^–1 is recommended for cucumber cultivation in drought-affected areas.