ULTRASTRUCTURAL STUDY ON THE EFFECTS OF SEED COAT FORMULATION NO. 17 ON WHEAT STRIPE RUST DEVELOPMENT IN HOST WHEAT
种衣剂17号包衣对小麦条锈菌发育影响的超微结构研究

The seedlings from wheat seed coated with seed coating formulation (SCF) NO. 17 containing fungicide triadimenol and other chemicals were inoculated with a virulent race of Puccinia striiformis West. The effects of SCF No. 17 on development of the fungus were examined with electron microscope. The results showed that SCF No. 17 caused a series of changes in the fuagal cell and host cell. The lipid bodies and vacuoles increased in the cytoplasm of hyphae and primary haustoria. The appearance and accumulation of electron-dense vesicles between the fungal plasmalemma and walls made their walls thickened irregularly, and wall thickening at hyphal top was very obvious. Septum did not form at hyphal branch or septal wall did not extend to hyphal cell center because of appearance of electron-dense vesicles. Some haustorial mother cells produce malformed penetration pegs which did not penetrate through host cell wall. It was observed that the extrahaustorial matrix of primary haustoria became enlarged and contained some electron-dense material, and the secondary haustoria formed several branches but did not generally expand at all. With the degeneration of hyphae, some electron-dense material leaked into host intercellular space from the .hyphae, the material may cause death of host cells. Most infected host cells secreted larger callose which usually extended beyond the joint part between the neck and body of haustoria. Sometimes the material secreted by infected host cell enclosed whole haustorium. The results from electron microscope observation indicated that SCF No. 17 not only directly acted on the fungus, but also indirectly affected it by influencing host, and host cell necrosis was not the inhibition cause of the fungal development.