INDUCTION OF SYSTEMIC DISEASE RESISTANCE IN CUCUMBER PLANTS TREATED BY THE SPRAY OF SOME BIOTIC AND ABIOTIC AGENTS TO CONTROL DOWNY MILDEW DISEASE

Abstract

Certain amounts of inducers, i.e Salicylic acid, Oxalic acid, and yeast extract as biocontrol agent as well as the fungicide Aquacid, used as foliar spray treatments proved to be effective in reducing downy mildew severity (DS) caused by ( P s e u d o p e r o n o s p o r a c u b e n sis ) on cucumber plants under greenhouse and field condition. In vitro , the tested fungicide, resistance inducing chemicals (RIC) and biocontrol agent highly inhibited sporangial germination of P . cubensis fungus compared with the control, Aquacid fungicide and the biocontrol agent were more effective on sporangial germination than chemicals RIC. Under greenhouse condition, severity of downy mildew disease decreased, significantly. Some Plant growth parameters i.e Plant length and fresh weight were significantly increased when the fungicide and RIC were applied as compared with the control. In field experiments, foliar application with fungicide Aquacid (2.5g/L) as a comparison treatment, Salicylic acid, Oxalic acid, and the yeast extract in concern, significantly reduced the disease severity of downy mildew with the averages of 7.25, 25.43, 30.0 and 16.40 %, respectively compared with untreated plants in the first season 2016 and the same trend was cleared in the second season 2017 with the averages of 6.50, 24.15, 25.45and 13.33%, respectively. Moreover, all exercised treatments significantly increased all of the studied growth parameters, i.e. plant length, leaves number, number of flowers, fresh and dry weight/plant. The treatments showed remarkable increase physiological aspects (Peroxidase activity and total phenol content) and similar reduction in disease severity of downy mildew revealing the most superior positively correlation with both peroxidase activity and total phenol content.