INDUCTION OF RESISTANCE TO POWDERY MILDEW DISEASE OF SQUASH PLANTS

Abstract

In the current study the first two true leaves (lower leaves) of squash seedlings (14 days old) were sprayed ones with a known concentration of aqueous solutions of different chemical compounds or with the systemic fungicide Topas-100 (Penconazole) at 25 ppm. Spraying with tap water served as control. Two days after foliar application the lower leaves were inoculated with conidia of Sphaerotheca fuliginea. The upper 3 leaves that expanded after treatment were left to natural powdery mildew infection under greenhouse conditions. At the proper time different measurements were recorded mainly on the upper leaves that expanded after foliar treatment. The results obtained during this work could be summarized as follow: 1. Conidial germination was inhibited completely (100.0%) by both the fungicide Penconazole and CuS04 while Ascorbic acid (AsA), KH2P04, MnS04, Salicylic acid (SA), CaCh, Boric acid (BA), Oxalic acid (OA) and CoCh reduced it by 92.9, 82.1, 67.1, 58.9, 54.3, 53.2, 51.8 and 30.2%, respectively. Whatever, SA at 5mM, OA at 20mM and CoCh at 5mM did not affect spore gennination significantly compared with control. 2. On the lower sprayed leaves, average nwnber of powdery mildew (PM) colonies but not disease index (DI) was reduced significantly by all tested compounds compared with control. Whatever, the fungicide Penconazole was the superior treatment, reduced both PM colonies and DI by 100.0%. Beyond fungicide, KH2P04 at 100 & 200mM were the best for decreasing PM colonies (92.3- 92.4%) followed by AsA at 20mM (83.5%), SA at 10mM (81.2%)