Evaluation of the Effect of Foliar Application of Brassinosteroid on Physiological Characteristics and Yield of Rapeseed Genotypes Under Late-Season Drought Stress

In order to study the effect of brassinosteroids on yield and physiological characteristics of rapeseed genotypes under late-season drought stress, a factorial split-plot test is conducted in a randomized complete blocks design with three replicates for two cultivation years (2017-2019) in the research farm of Islamic Azad University, Karaj (Mahdasht). Experimental treatments include two levels of brassinosteroid (0 (the control) and 0.1 μmol) and two levels of irrigation (full irrigation (the control) and withholding irrigation from 50% flowering stage) as factorial in the main plots, with rapeseed genotypes (Nafis, Ahmadi, Okapi, Nima, and Niloofar) being considered as subplots. Foliar application of brassinosteroid under both full irrigation and withholding irrigation from the flowering stage increase seed yield, chlorophyll, and relative water content, compared to the control. The highest amount of soluble carbohydrates, leaf proline, and oil percentage have been obtained under drought stress and brassinosteroid application, i.e. 24.8%, 16.5%, and 2.5%, respectively, compared to the control conditions. However, Okapi genotype has had the highest stomatal resistance (24.59 s/cm), the lowest chlorophyll (1.49 μmolg-1FW), and seed yield (1960.5 kg/ha) in the conditions of withholding irrigation. Niloufar genotype has had the lowest stomatal resistance, the highest chlorophyll, oil percentage, and seed yield in both irrigation conditions. In general, in both irrigation treatments, the use of brassinosteroids improve physiological traits of rapeseed.