Abstract
Several cationic surfactants were tested for their inhibitory activities against powdery mildew of cucumber. Among alkyltrimethylammonium chloride, the octyl derivative was the most effective on the powdery mildew, but caused a little phytotoxicity. Alkyldimethylbenzylammonium chloride used in this experiment showed low effects. Didodecyldimethylammonium bromide was remarkably effective, and caused on phytotoxicity on cucumber plants. Inhibitory effects of didodecyldimethylammonium bromide were observed at various growth stages of the cucumber powdery mildew fungus (Sphaerotheca fuliginea), namely, conidial germination, appressorial formation, haustorial formation, hyphal growth, and sporulation. The compound was effective on the fungus at all stages of the life cycle, especially at haustorial formation, hyphal growth, and sporulation. Also the stained mycelia of this fungus showed a speckled, collapsed membrane system and death of hyphal cell were observed frequently. These results suggest that didodecyldimethylammonium bromide act on the cell membrane.
