Stimulation of Sexual Reproduction of Phytophthora cactorum by Phospholipids

Abstract

Summary: In a chemically defined liquid medium, soybean lecithins (99% pure) were much more effective than, β-sitosterol and cholesterol in stimulating oospore formation by isolate Pct N of Phytophthora cactorum at 20 and 24 °C. Assuming that the 1% impurity is all sterols, such sterol impurity would account for less than 2% of the oospores produced in the presence of lecithins. Lecithins were also stimulatory to sexual reproduction of Phytophthora capsici and Pythium aphanidermatum but notPythium vexans, whereas sterols were stimulatory to sexual reproduction of Pythium aphanidermatum and Pythium vexans but not Phytophthora capsici, Lecithins from soybean were more effective in inducing sexual reproduction by isolate 121F of Phytophthora cactorum than were those from egg yolk. L-α-Phosphatidylethanolamine from soybean was as effective as lecithins in inducing sexual reproduction, whereas L-α-Phosphatidylinositol from soybean and L-α-Phosphatidyl-L-serine from bovine brain were ineffective. Of four synthetic lecithins tested, only dioleoyl-L-α-Phosphatidylcholine was active. The triglycerides and fatty acids tested were inactive. The results suggest that the activity of lecithins is determined by the type and position of fatty acids in the molecular structures.