Application of 24-epibrassinolide decreases the susceptibility to cucumber mosaic virus in zucchini (Cucurbita pepo L)

Brassinosteroids (BRs) are involved in a wide range of developmental processes and response to biotic and abiotic stresses. However, the roles of BRs in defense against virus in economically important crops have not been studied. Here, we showed that application of 24-brassinolide (EBR), a biologically active BR, at 0.2 μM was effective in decreasing the incidence of infection by cucumber mosaic virus (CMV) in susceptible zucchini (Cucurbita pepo L) plants. EBR reduced the accumulation of CMV in systemic leaves but not in inoculated leaves. CMV infection caused oxidative stress, abnormal chloroplast structure and damages to the photosynthetic apparatus. However, EBR treatment ameliorated the symptoms caused by CMV. EBR-induced defense to CMV is not accompanied by accumulation of salicylic acid. In contrast, EBR treatment alone induced a transient accumulation of H2O2. Subsequently, EBR treatment led to an increased accumulation of H2O2 during the early phase of CMV infection. The results suggest that application of EBR could be a promising approach to control virus disease in susceptible crops and EBR-induced oxidative burst may play a role in defense to virus disease.