Effect Of 24-Epibrassinolide Induced The Resistance Of Grapevine Against Downy Mildew And Grape Against Grey Mould

Downy mildew and grey mould, considered as the fungal disease of grapevine leaf and grape, are detrimental to grape quality and quantity. Brassinosteroids(BRs) are a class of steroidal plant hormones that are involved in regulating a series of plant growth and development, and have been widely investigated. There is also increasing evidence that BRs have a protective function on enhancing various resistances. The study consists of two parts: exogenous 24-epibrassinolide(EBR) induced the resistance of leaf against Plasmopara viticola invading and its mechanism, and EBR induced the resistance of grapes during storage to control grey mould.Cabernet Sauvignon(Vitis vinifera L.)and Redglobe(Vitis vinifera L.) were used for experimental materials. Three EBR treatments and one control were made for both trial. The study consisted of(1) the stomatal aperture, endogeous plant hormones content, growth and development of P. viticola spore and disease incidence and disease severity of downy mildew, and(2) disease severity, lipid peroxidation and defense-related enzymes of stored berries. The main results were listed as follow:(1) At the early development of P. viticola invading grapevine leaf, all of EBR treatments(0.1 mg/L, 0.5 mg/L, 1.0 mg/L) significantly controlled the disease incidence and disease severity, and the leaves treated with 0.5 mg/L and 1.0 mg/L had a lower disease incidence and severity of downy mildew, while disease incidence was decreased by 51.4% and 45.0%,and disease severity drop by 71.2% and 62.9%. There is no significance between the two treatments;(2) Exogenous EBR displayed the resistance against P. viticola invading the grapevine leaf by the decrease of stomatal aperture, number of spores per stoma and P. viticola growth. 0.5mg/L and 1.0mg/L EBR had a higher resistance while there is no difference between the two treatments. Results showed that a decrease of 63.7% and 77.8% of stomatal aperture, 14.6% and 15.2% of number of spores per stoma, 48.0% and 55.3% linear length of P. viticola colonies for 0.5 mg/L and 1.0 mg/L treatment.(3) 0.5mg/L EBR-treated leaves had a significant difference with control on the endogenous hormone including ABA, SA and JA. The stomatal aperture had significantly positive correlation with SA content, and ABA content had significantly positive correlation with JA content. The increased resistance against P. viticola invasion was possibly related with the suppression of pathogen development and the stomata closure which plant hormone crosstalk involved in.(4) All EBR treatements(0.1 mg/L, 0.4 mg/L, 0.8 mg/L) had a significantly decreased the severity of grey mould. Berries treated with 0.4 mg/L EBR decreased the severity by 16.3% ~ 37.9%;(5) EBR-treated grapes had a lower content of O2.- and MDA. 0.8 mg/L EBR resulted in a lowest amount of O2.-, and it had a 5.4% ~ 77.0% decrease compared with control. 0.4 mg/L and 0.8 mg/L EBR had a lower MDA, separately decreased by 1.6% ~ 14.5% and 4.1% ~ 8.0% leading to decreased lipid peroxidation level. All EBR-treated berries resulted in an increase of activities of defense-related enzymes including superoxide dismutase(SOD), peroxidase(POD), catalase(CAT), and phenylalanine ammonia-lyase(PAL) compared with control berries inoculated by B. cinerea. Berries treated with 0.4 mg/L EBR had a higher defense-related enzymes activity.Conclusively, EBR treatment increased the resistance of grape against downy mildew and grey mould. 0.5 mg/L and 1.0 mg/L EBR treated grapevine leaves had a more suppressed early development of P. viticola compared with control. For table grapes during storage, EBR treatment resulted in a lower grey rot severity and 0.4 mg/L and 0.8 mg/L EBR reached the lowest one. The increased defense-related enzymes and the drop of lipid peroxidation level were possibly related with the induced resistance.