Foliar sprays of nine abiotic agents namely; ascorbic acid, boric acid, calcium chloride, cobalt chloride, copper sulphate, manganese sulphate, oxalic acid, potassium di-hydrogen phosphate and salicylic acid, were tested to evaluated their efficacy to induce resistance against Sphaerotheca fuliginea, the causal of powdery mildew of squash (Cucurbita pepo L.) under glasshouse conditions. All tested foliar treatments, except CaCl2, were effective in inducing systemic protection against powdery mildew. However, they were less effective than penconazole which was equally effective as MnSO4 at 20 mM as they caused a 100% systemic protection on the upper leaves. Among the tested agents, six have significantly increased sugar content of leaves, while all of them decreased the total phenols compared to the control. Out of the tested agents, MnSO4, salicylic acid, oxalic acid and boric acid enhanced the peroxidase activity. However, polyphenoloxidase activity was affected only by oxalic acid, MnSO4 and KH2PO4 as they highly increased it to the control. In addition, it was found that most of the tested compounds caused significant increase in the total soluble protein of the 4th leaf.
Key words: Sphaerotheca fuliginea, squash, control, induced resistance, phenols, sugars, peroxidase, polyphenol oxidase and proteins.
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