1.4.30
SYSTEMIC ACQUIRED RESISTANCE IN GREENHOUSE CUCUMBER FOR CONTROLLING DOWNY MILDEW USING SALICYLIC ACID AND ACETYLSALICYLIC ACID

MM ALY1, WE ASHOUR1, F ABD EL-KAREEM2 and MM DIAB2

1Faculty of Agriculture, Ain Shams University, Shoubra El-Kheima, Cairo, Egypt; 2National Research Center, Cairo, Egypt

Background and objectives
Downy mildew caused by Pseudoperonospora cubensis is one of the most important diseases of cucumber (Cucumis sativus) in Egypt, especially under greenhouse conditions. Control of this disease depends mainly on fungicides, which cause hazards to the environment and human health. The present work was aimed to investigate systemic acquired resistance (SAR) using salicylic acid (SA) and acetylsalicylic acid (ASA) as a mean for controlling this disease [1-4].

Materials and methods
Different concentrations of SA or ASA were tested as seed or seedling treatments. Seeds were soaked in aqueous solution of SA 2.5, 5.0 or 7.5 mM or ASA 5.0, 10.0 or 15.0 mM for 24 h before sowing [4]. Seedlings were sprayed with a solution of SA or ASA at the same concentrations, i.e. 2.5, 5.0 or 7.5 mM, at the first leaf stage. Booster treatments with the same concentration as the single treatments were applied in commercial greenhouses at the seventh leaf stage. Disease assessment was carried out according to Reuveni [2].

Results and conclusions
Pot experiments revealed that all the tested treatments induced SAR and significantly reduced disease severity. The most effective concentration was 5 mM of SA or ASA when applied as seedling treatment. Both treatments affected sporulation of the causal fungus, the number of conidia/cm2 of lesion reduced to 8.5 and 10.3% of the untreated control for ASA and SA (5.0 mM), respectively. Greenhouse experiments assured the efficiency of these treatments in controlling the disease. The effect of these treatments lasted until 70 days after sowing and then decreased. Booster treatment at the seventh leaf stage revealed higher efficiency of SAR, but had no effect on durability. ASA was the most effective treatment, followed by SA, reducing disease severity by about 77 and 66%, respectively, compared to 53% with the fungicidal treatment. They increased fruit yield by 58 and 38% as compared to 26% with the fungicidal treatment. Studying the response of different cultivars of greenhouse cucumber to the inducing treatments [ASA and SA, 5 mM] showed that they varied in their response with both treatments. It could be concluded that 5-mM ASA seedling treatment followed by a booster treatment at the seventh leaf stage is promising for controlling downy mildew of greenhouse cucumber. This treatment has an extremely low cost/benefit ratio compared to the fungicidal control.

References
1. White RF, 1979. Virology 99, 410-412.
2. Reuveni R, 1983. Annals of Applied Biology 102, 533-537.
3. Aly MM, Habib SA, Abd-Allah SM, 1988. Proceedings of the 2nd Conference on Agricultural Development Research, Ain Shams University, Cairo. 4. Kataria HR, Wilmsmeier B, Buchenaver H, 1997. Plant Disease 46, 897-909.