Citokinin-mediated Suppression of Cucumber Powdery Mildew Disease: 6-benzyladenine Suppresses the Growth of Cucumber Powdery Mildew Fungus, Sphaerotheca fuliginea

The effect of a cytokinin, 6-benzyladenine (6-benzylamlnopurine, BA), on the growth of a powdery mildew fungus was investigated. The growth of Sphaerotheca fullginea on cucumber leaf disks was suppressed by BA treatment and the suppressive effect of BA was dose-responsive. Compared with H sub(2)O treatment, treatment of the leaf disks with 500 mu M BA decreased the number of haustoria and total hyphal length per one colony, but not with 5 mu M BA. Observation of the hyphal growth using a light microscope showed that BA treatment suppressed the elongation and branching of hyphae by S. fuliginea. BA treatment for short period suppressed the formation of conidiophores 96 h post inoculation. Interestingly, the formation of conidiophores was also suppressed even if BA was treated at the later infection processes of S. fuliginea. These results suggest that the suppressive effect of BA on the growth of S.fuliginea is durable and immediate. On cotyledons inoculated with S. fullginea, BA treatment suppressed the disease symptoms formed by S. fuliginea and hence decreased the source of secondary inoculum. These studies might contribute to the development of unique disease management systems to control powdery mildew diseases using plant hormones.