Study On The Wilt-Resistance Mechanism Of Chieh-qua

Fusarium wilt caused by Fusarium oxysporum f. sp. Schl is a major factor limiting commercial Chieh-qua production in South China. At present there aren't effective prophylaxis and remedy methods to control the desease; therefore, it's important to breed desease-resistant cultivated varietis. Based on the previous study and successful establishment of toxin-resistant variety, a resistant cultivar A02, a susceptible cultivar A06 and a toxin-resistant variety LT seedlings were inoculated with Fusarium oxysporum, meanwhile, the three varieties seelding were treated with fusaric acid, then the dynamic change process of biochemical and physiological changes were determined, and the ultrastructure changes in stem tissue and eotyle tissue were investigated. So that the wilt resistance correlative physiologic and biochemical criterion were found out, and the antagonistic mechamism was studied. The main results were as follows:1. Before the wilt disease occured, there were not singnificant difference between the content of chlorophyll and dissociate proline in the susceptible type (S-type) and that of the resistant types (R-types); the activities of POD and PPO of the R-type were higher than that of the S-type; the content of soluble protein of the R-type were lower than that of the S-type. After the wilt disease come on, the S-type showed larger decreasint rates of cholrophyll and soluble protein than the R-types. The S-type showed higher increasing rate of proline content than the R-types. The activities of POD and PPO of the R-types were far higher than that of the S-type; furthermore, the activities of POD and PPO resistant variety maintained in the higher level even all the while. Therefore, at seedling stage of Chieh-qua, the contents of chlorophyll and soluble protein, the activities of POD and PPO in leaves can be as the critical indicators for screening wilt-resistance material.2. Under the condition of fusarium acid stress, the content of chlorophyll a and b of the S-tpye first increase and then decrease; the content of dissociate proline of the S-type increase rapidly; the S-tpe showed slow increase speed and lower increase extent of the activity of POD, but it showed fast increase speed in the activity of PPO. The content of chlorophyll a and b in eaves of the R-types maintain stably in the original level; the content of free proline of the R-types increased slowly; the activity of POD of the R-types increased rapidly within prior 2hs, and then maintain in the high level after that; the R-types showed slow increase speed and low increase extent of PPO activity; the content of soluble protein in leaves of three varieties rise steadily, and the content of soluble protein in leaves of the S-type was always higher than the R-types.3. The results of the comparison of the fusaric acid effect and the Fusarium oxysporum effect on the biochemical and physiological changes indicated that there was a certain correlation between the wilt-resistance and the toxin-resistance.4. Under the condition of fusarium acid stress for lh, ultrastructure studies were performed on the stem cells and the cotyledon cells. In stem cells of the S-type, endomembrane system of the chloroplast was destroyed, the grana lamellae be disorganized; tylose and gum could be observed in vessels; mitochondrion retain normal. In S-type cotyledon cells, chloroplast membrane was damaged, lamellae was in disorder, cell wall was out of shape and plasmolysis was observed, yet the mitochondrion retain normal. The effects of FA on S-type's ultrastructure were heavier than on the R-type.