Study On Effects Of Pathogen Alternaria Azukiae (Hara) Comb. Nov.on Physiological-ecology Characteristics Of Host Plant Trifolium Repens L.

The interactions between pathogens and their host plants, which are very common in nature plant populations, have been studied as a focus by western ecologists since 1980s. Study on the relation of pathogen to host plant may give convenience to discovery the regulation of interaction between them and form the base of mechanism of resistance to disease of host plant and inheritance breeding of disease free. The host T. repens is a perennial herbaceous plant. It is common that this plant is infected by pathogen A. azukiae in nature. In the long run of co-evolution, they have set up steady relation. This paper relates to the effects of physiological and biochemical characteristic of T. repens infected by A. azukiae. The results showed below: 1 When host plant T. repens infected by pathogen A. azukiae, significant difference existed in the morphology and anatomy structure of leaf epidermis. Under light microscope, the shapes of lower epidermis cell of normal leaves and the diseased ones were different obviously. The lower epidermis cells of normal leaves were sinuate and the diseased ones were near circular. There were significant differences on anatomy structure of normal leaves and diseased ones. The majority of the diseased plant cells damaged by pathogen were curly and wizened. Thus normal functions of organs were affected. 2 When T. repens infected by A. azukiae, the cell membrane permeability, pigment content, MDA content and activities of SOD, POD, CAT were different form normal ones. The cell permeability, electric conductivity, content of MDA increased, but pigment content decreased. The electric conductivity and the content of MDA showed positive correlation with infection time, but pigment content was negative with infection time. Due to the stimulation by A. azukiae, the over-oxidation of cell membrane was intensified. At the same time, a large amount of active oxygen was accumulated, which the defense of enzyme system didn't eliminate thoroughly. Therefore, the active oxygen metabolism system was destroyed, the balance of protective enzyme system was broken. 3 In natural habitat and under different light intensities, the physiological and biochemical characteristic of host plant T. repens also showed some differences from normal ones when infected by A. azukiae. After infected, the cell membrane permeability of leaf of host plant increased. The electric conductivity and content of MDA showed negative correlation with intensity of light. However, the pigment content, protein content and proline content was negative with intensity of light. Under the stimulation of pathogen, the cleaning system of oxygen was destroyed, the protective enzyme was also forced out its balance, the activity of SOD and POD decreased, comparatively the activity of POD increased. The three enzymes had significantly negative relation with the intensity of light. 4 Differences existed in cell membrane permeability, pigment content and activity of SOD,POD and CAT among different populations of host plant T. repens infected by pathogen A. azukiae was studied. The results might come from the adaption of host plant and pathogen of their survival strategies to surrounding living habitation when they lived in the same environment.