Comparative Analysis of Exogenous Hormone Application on Contrasting Canola (Brassica napus L.) Genotypes Under Drought Stress Conditions

Drought stress adversely affects the quantity and quality of canola. A 2-year experimental study was conducted to examine the role of exogenous cytokinin, epibrassinolide, and their interaction in alleviating drought stress damage on drought-sensitive (Okapi) and drought-tolerant (GKH) canola cultivars. The experiment was conducted using a split-plot factorial arrangement within a randomized complete block design. Then, the agronomic and physiological traits were evaluated with four foliar treatments (distilled water, cytokinin, epibrassinolide, and cytokinin + epibrassinolide) at two levels of field capacity and water withholding at the flowering stage. Drought stress decreased plant biomass by 50% and declined grain yield and oil yield by 33% and 30%, respectively. In GHK and Okapi cultivars, this results in membrane lipid peroxidation and relative water content reduction, as well as a reduction in chlorophyll content during flowering. As compared to field capacity treatment, foliar application of epibrassinolide increased grain yield and oil yield by 93% to 128% in drought-stressed plants. In addition, foliar application of cytokinin and epibrassinolide significantly increased the activity of peroxidase and catalase enzymes and chlorophyll levels in both canola cultivars under drought stress, resulting in improved membrane stability, relative water content, and photosynthesis rates. After epibrassinolide foliar application, MDA and cell electrolyte leakage significantly and negative were correlated with dry weight, oil yield, and grain yield. It was found that EBL foliar application resulted in reduced membrane damage, improved yield, and increased antioxidant capacity, therefore alleviating drought stress, especially in the GKH cultivar.