Abstract
Effects of polyoxin on infection process of Sphaerotheca fuliginea (SCHL.) POLLACCI were investigated by light and scanning electron microscopies. Conidia were inoculated to cotyledons of cucumber which absorbed polyoxin from roots. About 70% of conidia were inhibited to germinate by 50-500 ppm of polyoxin. Furthermore, about 20% of conidial germ tubes swelled by 50 ppm polyoxin treatment, and 87 and 86% did by 200 and 500 ppm treatment, respectively. Similarly, tips of secondary hyphae swelled by polyoxin treatment. Higher concentration of polyoxin induced more number of the swelling tip. As the result, branching of hyphae decreased in number and mycelial colonies developed poorly on cotyledons treated by higher concentrations of polyoxin. The present results suggested that polyoxin effects on cucumber powdery mildew were the inhibition of penetration activity by the induction of swelling germ tube and the suppression of mycelial growth by the inhibition of hyphal branching.
