Effect of some Resistance Chemical Inducers on Incidence of Cucumber Fusarium wilt caused by Fusarium oxysporum f. sp cucumerinum

Cucumber Fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum (FOC), is one of the most important cucumber diseases in Egypt. Effects of four different resistance chemical inducers (RCIs) on linear growth of FOC, controlling Fusarium wilt and inducing systemic resistance were investigated under laboratory and glasshouse conditions, using Al-Zaeem cultivar as a susceptible cultivar and Hayel cultivar as a resistant one. Results indicated that reduction in the mycelial growth of FOC increased with the increase of RCI concentration being greatest with oxalic acid and salicylic acid treatments. Tested RCIs significantly reduced wilt disease incidence in cucumber plants as compared with control in both cultivars. Highest percentages of healthy survived plants and disease reduction were recorded in oxalic acid treatment, followed by salicylic acid and citric acid treatments, whereas hydroquinone was the least effective RCI. The tested RCIs also increased plant growth parameters; plant height, root length, leaves number and fresh weight in both studied cultivars as compared to the control. Exogenous application of RCIs treatments resulted in significant increases in phenolic contents with subsequent significant increase in the phenol-oxidative enzymes, peroxidase (PO) and polyphenol oxidase (PPO). Greatest values of phenol content, activities of PO and PPO were recorded at oxalic and salicylic acid treatments. Phenol content and its related enzymes were higher in treatments previously infected by FOC than those grown in non-infected soils and also higher in resistant cultivar than in susceptible one.