Mitigation Effect of Exogenous Dopamine Treatment on Downy Mildew-Infected Cucumber
Ji, Ze-Yu, Ze-Yu Liu, Li-Ming Shi, Xin-Yu Lu, Yu-Ying Han and Yan Sun
Journal of Plant Growth Regulation
https://doi.org/10.1007/s00344-024-11290-2
ABSTRACT
Downy mildew is one of the main diseases that cause a reduction in cucumber yield. Chemical control not only increases pathogenic bacteria resistance and causes environmental pollution but also endangers the health of humans as they are abundant pesticide residues in fruits. Dopamine, a strong antioxidant that widely exists in plants, can effectively protect plants from the adverse effects of such chemicals. In this study, the susceptible cucumber cultivar 'Changchun Mici' and the disease-resistant cultivar 'Jinchun No. 4' were used as test materials to explore the alleviating effect of exogenous dopamine on cucumber downy mildew. After downy mildew infection, exogenous dopamine (100 mu mol L-1) had the greatest significant effect on improving the disease resistance of cucumber, increasing the activities of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase in cucumber, thereby reducing the accumulation of the superoxide anion and hydrogen peroxide in leaves, the content of malondialdehyde, and the relative electrical conductivity in leaves, which significantly improved the antioxidant capacity of cucumber. Simultaneously, exogenous dopamine increased the leaf wax content and trichome density; the activities of polyphenol oxidase, chitinase, and beta-1,3-glucanase; and the expression of CsPR1, so that the disease index was significantly reduced. As for nitrogen metabolism, exogenous dopamine significantly increased the activities of nitrate reductase, glutamine synthase, glutamate synthase, and glutamate dehydrogenase, as well as the content of nitrate nitrogen, whereas it decreased the accumulation of ammonium nitrogen, thereby promoting nitrogen metabolism in cucumber. As a consequence, exogenous dopamine improved the yield and quality of cucumbers infected by downy mildew.