Synergistic application of melatonin and silicon alleviates chromium stress in Brassica napus through regulation of antioxidative defense system and ethylene metabolism

•Chromium stress reduced growth of Brassica napus seedlings grown in chromium (Cr) contaminated soil.•2- hydroxymelatonin (2-HMT) and Silicon (Si) reversed the toxic effect of Cr stress through enhanced activity of antioxidative enzymes and reduction in malondialdehyde (MDA), hydrogen peroxide (H2O2) and electrolyte leakage (EL).•Co-application of 2-HMT and Si enhanced ethylene level in B. napus seedlings.