Abstract
Lecithin obtained from soybean plants at the time of producing soybean oil controls effectively several powdery mildews and rice blast disease. Since lecithin is a ubiquitous component in living organisms and its safety as a food additive is established, it is expected that this compound may be a safe agricultural fungicide and is applicable to vegetables even during harvest. Therefore, we examined the effect of lecithin on the growth of the cucumber powdery mildew fungus, Sphaerotheca fuliginea with a scanning electron microscope. After spraying 2000ppm of the lecithin on the lower surfaces of cucumber cotyledons, conidiospores of the pathogen were inoculated on the same place. Spore germination, hyphal elongation, conidiophore formation and sporulation were observed at certain intervals. The lecithin did not inhibit remarkably spore germination, but gave some effects on spore germination, hyphal elongation and sporulation. That is, germ tubes on treated lower surfaces were stunted and became shorter than that of control. Hyphal elongation on treated surfaces was delayed, and conidiophore formation and sporulation were poorer than those on control lower surfaces. It was a striking feature that hyphal tips on the lower surfaces of cucumber cotyledon treated with lecithin became deformed, namely thin membrane-like substance appeared around hyphal tips and expanded with time. More delayed and fewer conidiophores and conidiospores were observed on the lower surface treated with the lecithin than those on the control lower surfaces. In addition, many conidiospores which were unable to release from conidiospore chain were observed on conidiophores, and such conidiospores dangled like osmund from the conidiophores on lower surfaces of cucumber cotyledon treated with the lecithin.
