Ultrastructural And Cytochemical Studies On The Relationship Of Rhizoctonia Cerealis V.Hoeven And Its Host During Infection And The Influence Of Bayleton On The Pathogen

The wheat sharp eyespot is one of the major wheat diseases in our country, Rfiizoctonia cerealis V. Hoeven can infect both in adult stage and in seedling stage. seriously influencing production and quality of the wheat. In order to profoundly understand the essence of interactions between host and pathogen during Rhizoctonia cerealis infection and provide theory basis for controlling the disease, the infection processes of Rhizoctonia cerealis on leaf sheat and on coleoptile were observed by light microscopy and electron microscopy: the pathogen hypha produced infection cushions on host surface before penetrating and directly penetrated host cells with penetration pegs produced under infection cushions. The cell wall of infection hypha consisted of two layers, the inner layers extended and broke through outer layers to invade into the host cells while penetrating, then extended intercellularly and intracellularly. During the infection of pathogen, a series of pathological changes occurred in host tissues and cells, such as plasmolysis, disruption of cytoplasm, decomposed of organoids and necrosis of cells. The infection process of Rhizoctoina cerealis on leaf sheat was similar to that on coleoptile, but the extending speed on leaf sheat was slower than that on coleoptile. When Rhizoctonia cerealis penetrated host cells, the color of host cell walls around penetration pegs usually became shallower, probably pathogen produced cell-wall-degrading enzymes during infection. The cell-wall-degrading enzymes softened, decomposed the cell walls, contributed to the infection of pathogen.In order to further understand the chemical phenomena of interactions between pathogen and host during infection, the cell wall components such as cellulose, xylan and pectin in cell walls of uninoculated healthy and Rhizoctonia cerealis-infected wheat sheat were detected by means of cytochemical methods. All the cell walls of healthy leaf sheat tissues comprised cellulose, xylan and pectin, while these components were different in different type of cell walls. The components of Rhizoctonia cerealis-'mfecled wheat leaf sheat changed: the labeling densities for cellulose, xylan and pectin were significantly reduced as compared with corresponding cell walls of healthy leaf sheat. That phenomenon indicated that Rhizoctonia cerealis secreted cell-wall-degrading enzymes, such as cellulase, xylanase and pectinase during the infection of Rhizoctoinia cerealis on leaf sheat tissues, which decomposed and softened the host cell walls, then contributed to the penetration and extension of pathogen.After Rhizoctonia cerealis was operated by Triazoleferone (Bayleton) which was often applied to control the wheat sharp eyespot, the growth of the hypha became slower; the number of the vacuoles increased, while vacuoles further fused and became largerwith more or less sediment in them; the cell walls of the hypha thickened irregularly, especially at the tip of the hypha, while the cells near the thickened cell walls usually companied with a lot of vesicles; some hypha produced new hypha. Under the influence of the fungicide, the host secreted more sediment to resist the infection of pathogen. Which indicated that Bayleton not only directly acted on Rhizoctonia cerealis, but also enhanced host resisting ability to pathogen.