Ultrastructural And Cytochemical Studies About The Relationship Of Sclerotinia Sclerotiorum And Its Host During Infection And The Influence Of Metconazole On The Pathogen

The Sclerotinia sclerotiorum of rapeseed is one of the major disease of canola in the world. It is much severe in our country. Sclerotinia sclerotiorum can infect about 400 kinds of plants.In order to profoundly understand the essence of interactions between host and pathogen during Sclerotinia sclerotiorum infection and provide theory basis for controlling the disease,the infection processes of Sclerotinia sclerotiorum on leaf and stem were observed by light microscopy and election microscopy: At first, the pathogen hyphae grew -. extended on host surface , then produced infected cushions before penetrating .The tip of the rim hyphae on infected cushions were swollen and then directly penetrated host cells. Some infected hyphae extended intercellulary , some broke through cell wall and invaded into inner ,so extended intracellulary. At last the pith including xylem and phloem was infected by hyphae . During the infection of pathogen, a serious of pathological changes occurred in host tissues and cells,such as dissociation of cell wall, decomposed of plasmogen and necrosis of cells.The infection process of Sclerotinia sclerotiorum on leaf was similar to that on stem , but the extending speed on leaf was slower than that on stem. As soon as Sclerotinia sclerotiorum extended into vascular on leaf, the speed was the same to that on stem. When Sclerotinia sclerotiorum penetrated host cells , the colour of host walls around infected hypha 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 Sclerotinia sclerotiorum-infected rapeseed were detected by means of cytochemical methods. All the cell walls of healthy stem tissues comprised cellulose, xylan and pectin. The components of Sclerotinia sclerotiorum-infected rapeseed stem changed: the labeling densities for cellulose,xylan and pectin were significantly reduced as compared with corresponding cell walls of healthy stem. This phenomenon indicated that Sclerotinia sclerotiorum secreted cell-wall-degrading enzymes, such as cellulase, xylanase and pectinase during the infection of Sclerotinia sclerotiorum on stem tissues, which decomposed and softened the host cell walls, then contributed to the penetration and extension of pathogen.The effects of metconazole , a systemic fungicide from the triazol group were examined on morphology, structure, cell wall components of Sclerotinia sclerotiorum by means of electron microscopy and immunocytochemical labelling techniques. The studies revealed that metconazole not only inhibited the hyphal growth , but also caused a series of markedmorphological and structural alterations of hyphae. These changes included irregular swelling , excessive branching and many tumors on the surface of hyphae, considerable thickening of the hyphal cell walls, particularly at the hyphal tip region. The septum development of the hyphae was inhibited and became malformed . Using cytochemical techniques, the labelling densities of chitin and beta-1,3-glucan in the cell wall of the fungicide-treated hyphae were increased dramatically comparing with those of the untreated control hyphae, indicating that the detrimental effects of the fungicide on structure and function of the hyphal membranes resulted in the changes of the cell walls compositions.