Effect Of Different Nitrogen Forms And Concentration On Soil-Borne Disease Of Cucumber Fusarium Wilt

Cucumber Fusarium wilt is one of soil-borne diseases, and is also known as stem rot disease. Fusarium oxysporum f.sp. cucumerinum (FOC) is the causal agent of cucumber (Cucumis sativus L.) Fusarium wilt. The resistance mechanisms of cucumber to diseases include passive and active defense. Passive defense is mainly to form structure obstacles and chemical composition, such as cutin, wax, xylogen, etc. Active defense is mainly to form protein, which can affect cell permeability of pathogens or inactivate ribosome. Its reaction mainly includes the release of reactive oxygen species, the expression of defense gene, anaphylactic reaction and system resistance, etc. In the present study, the effects of different nitrogen forms and concentration on physiological and biochemical processes of cucumber Fusarium wilt were investigated to reveal the resistance mechanism of nitrate. The major goal of our research is to provide the theoretical basis for prevention and control of Fusarium wilt in cucumber.In this thesis, water culture experiments were conducted in greenhouse to study the effect of different nitrogen forms and concentration on cucumber Fusarium wilt. The effects of FOC infection on growth, disease index, photosynthesis, water uptake, leaf temperature, FA content and substance metabolism of cucumber seedlings were investigated to illustrate the resistant mechanism of nitrate. The main results are listed as follows.1. Plant growth was markedly increased in nitrate nutrition as compared to ammonium grown plant. At the same nitrogen concentration, ammonium grown plant had slightly higher net photosynthesis rate, stomatal conductance, intercellular CO2 concentration, transpiration rate as compared to nitrate grown plant. However, the total nitrogen content of root, soluble sugar content of leaf in ammonium grown plant were significantly higher than that of different concentration nitrate grown plant. FOC infection significantly inhibited the photosynthesis, water uptake and disturbed the substance metabolism of ammonium grown plant while had no significant effect on nitrate grown plant, except 2 mM nitrate treated plant.2. Nitrate nutrition significantly suppressed disease index of cucumber Fusarium wilt as compared to ammonium nutrition under different concentration. The speed of pathogenesis increased and the duration from plant disease to death decreased as the concentration of ammonium nutrition increase. However, its contrast to the results of different concentration nitrate grown plant.3. After FOC infection, FA content in leaf and stem of the ammonium grown plant were significantly higher than nitrate grown plant and it increased as the concentration of ammonium nutrition increased.While no significant difference was found in root and significantly lower than different concentration nitrate grown plant.There was no significant difference in FA content in leaf,stem and rootn of different concentration nitrate grown plant.