Studies On Pathogenic Detection And Effects On Physiological And Biochemical Indexes Of Astragalus Membranaceus After Infected With Different Pathogenic Fungi

Astragalus membranaceus, a perennial herb, has the very high medicinal value and its root is used as medicine. In recent years with the expansion of planting area, shortening the period of rotation, and so on, root rot is becoming more and more serious and has become an important factor restricting the sustainable development of Astragalus membranaceus. Root rot of Astragalus membranaceus is a recurrent soil-borne disease. Fusarium oxysporum, Fusarium solani and Fusarium acuminatum are mainly pathogenic fungi. So far, researches on root rot in China are mainly concentrated in the investigation of disease, pathogen identification, histopathology, pathogenesis regularity and influence factors, while reports in physiological and biochemical changes in the pathogenesis of Astragalus membranaceus are rarely. In order to determine fungi pathogenicity and study the physiological and biochemical changes of Astragalus membranaceus in the process of root rot, the plants of Astragalus membranaceus are induced by being inoculated with Fusarium oxysporum, Fusarium solani, Fusarium acuminatum and mixed fungi artificially under the experimental conditions. The changes of10indixes including superoxide dismutase （SOD）, catalase （CAT）, peroxidase （POD）, ascorbate peroxidase （APX）, malondialdehyde （MDA）, H₂O₂, chlorophyll, soluble sugar, soluble protein and proline are measured every seven days during the process of root rot. Through the analysis of the changes of these indicators following the changes in physiological and biochemical metabolism of Astragalus membranaceus in the process of root rot, induced resistance mechanism is investigated to provide a scientific basis for effective control and prevention of Astragalus membranaceus root rot. The main results are as follows:1. The results of pathogenic detection on Astragalus membranaceus show that Fusarium oxysporum, Fusarium solani and Fusarium acuminatum have different levels of pathogenicity. The disease index is97.6%,51.9%and43.1%respectively. Pathogenicity of Fusarium oxysporum on Astragalus membranaceus is highest, Fusarium solani is higher. The disease index caused by the mixture of Fusarium oxysporum, Fusarium solani and Fusarium acuminatum is up to100%.2. When Astragalus membranaceus inoculated with Fusarium oxysporum, Fusarium solani, Fusarium acuminatum and the mixture become rotten gradually, the activities of superoxide dismutase（SOD）, catalase（CAT） and peroxidase（POD） increase first but decrease afterwards, and the activities of SOD and CAT peak within7days while the activity of POD peak within14days the activities of APX increase in the4treatment groups. There are some differences in changes of SOD, CAT, POD and APX among the4treatments. In order to compare the different enzymes in single Astragalus membranaceus, the activity of SOD、CAT、POD and APX differed little among the same place leaves in the same plant by comparision，which bore testimony to the relative stability of the four sorts of enzyme’s distribution in the leaves of the same plant.3. Astragalus membranaceus on the infected and control samples of MDA and H₂O₂content are compared. The content of MDA in infected plants at the early stage of disease stress do not change significantly and increase gradually after Astragalus membranaceus inoculated with Fusarium oxysporum, Fusarium solani, Fusarium acuminatum and mixed fungi within14days compared with control group. And the tendency of the content of H₂O₂is similar to that of the content of MDA.4. After Astragalus membranaceus inoculated with Fusarium oxysporum, Fusarium solani and Fusarium acuminatum, the content of chlorophyll in infected plants decrease by48.35%,45.47%and45.52%respectively compared with control within twenty-eighth days. While the content of chlorophyll in infected plants inoculated with mixed fungi decrease greatly by62.73%compared with control.5. The content of soluble sugar and soluble protein increase first but decrease afterwards, and peak within14days when the time for treating is prolonged compared with control group. The content of proline gradually increase among4treatments.