Observation on cell ultrastructure of pumpkin seedling leaves infected by powdery mildew fungus
In order to reveal the structural response mechanism of the interaction between pumpkin(Cucur-bita moschata)and powdery mildew fungus(Podosphaera xanthii),the ultrastructural changes of the high-resistant pumpkin inbred line 03112-2 leaves inoculated with P.xanthii at seedling stage were ob-served.The results show that when the spores of powdery mildew pathogens buded and formed hyphae,the cytoplasm effluxed,and haustoria were formed in the host cells to obtain nutrients from the host.Haustoria existed between cell walls and cell membranes of host cells,and were formed by the invading spikes produced by powdery mildew pathogens appressoria penetrating cell walls.The host resisted the invasion of pathogens through structural reactions such as thickening of cell walls,formation of T-shaped and hemispherical papillae,and increasement of contents and vacuoles.Powdery mildew pathogens caused swelling and deformation of chloroplasts in mesophyll cells of palisade tissue,serious accumula-tion of starch grains,destruction of basic structure,and separation of cytoplasmic walls in some epider-mal cells.Therefore,after inoculation with powdery mildew pathogens,pathogens obtain nutrients through haustoria,and the host resists the invasion of the pathogens by forming papillae and thickening cell walls,as well as the mesophyll cells with the changes of chloroplast swelling and plasmolysis.
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