Study On Morphology And Anatomy Of Astragalus Membranaceus Roots Infected By The Root Rot Disease

Astragalus membranaceus is a perennial herb plant,belongs to Leguminosae family.Its root is used as a traditional medicine,which is warm in nature and sweet flavor and can replenish qi to strengthen exterior,it is a very high medicinal value in Chinese herbal medicine. Astragalus membranaceus is tolerant of drought and cold climate,is very suitable for artifical cultivation in West.Weiyuan County,Zhang County,Longxi County,Min County and Lintao County of Dingxi City are the main producing areas of A.membranaceus in China,so Dingxi City is honored as "hometown of Chinese A.membranaceus".In recent years,with the market continuing to increase in the demand for A.membranaceus;the planting area of medicinal A.membranaceus constantly expanding and the cycle of rotation shortened,which have been resulted in increasing greatly of A.membranaceus root rot disease,and has became one of the important factor that impacted the yield and quality.Astragalus membranaceus root rot is soil-borne diseases,which is resulted by in common of soil pathogens and nematodes. Fusarium is the main pathogenic bacteria of causing Astragalus membranaceus root rot,which are Fusarium oxysporum and Fusarium solani by the pathogens were isolated,cultivated and identificated.At present,the study on Astragalus membranaceus root rot is mainly focus on macroscopic symptoms observation,pathogen separation and identification,anti-bacterial active substances screening.However,the less study on the anatomical structure and surface scanning structure of Astragalus membranaceus roots infected by root rot,and the pathogenic mechanism of Astragalus membranaceus root rot.For this reason,in this experiment,the root morphological characteristics,the surface and the anatomical structure of Astragalus membranaceus roots infected by root rot disease,the way of pathogenic fungi invaded and the distribution of the fungi in the root were studied used LM,TEM,SEM,taking the healthy roots as comparison.In order to understand the process of fungi infected.The result provide the theory basis for deeply researching the pathogenic mechanism and prevention and control of Astragalus membranaceusroot rot.The main findings are as follows:1.The morphological characteristics of the healthy roots and different time of Astragalus membranaceus roots infected by root rot disease were observed.The results showed that after the disease infection,root skin rough and brown,and some brown concave spots at the surface.With the deterioration of the illness,concave spots unceasingly increasing,the root shrinking and dry rotted,lateral root rotted and fall off, and the root system rotting and exfoliation.2.The anatomical structure of Astragalus membranaceus roots were studied by paraffin sectioning and free-hand sectioning.The results showed that the secondary structure was consist of periderm and secondary vascular tissue, and it belonged to the typical structure of dicotyledon root.The outermost layer of the root was periderm, it was consists of cork layer,cork cambium and phelloderm,and protect the root.The secondary vascular tissue was consists of secondary phloem,vascular cambium and secondary xylem.Secondary phloem accounted for about1/3of the root,the xylem was2/3,and there was no pith in the root.There were a large number of cell ergastic substance in the vascular tissue parenchyma cells,many starch grains,Needle-shaped crystal in few phloem parenchyma cells.3.The anatomical structure of Astragalus membranaceus roots infected by root rot disease were studied by paraffin sectioning and thin sectioning.The results indicated that the only difference on the basic anatomical structure was that the fungi invaded in the diseased roots and many hyphae or pelotons in parenchymatous cells.The fungi didn’t infected the periderm,they entered the phloem parenchymas through periderm,and then,formed pelotons,colonized and infected other cells continuously by means of hypha penetrating the cell wall,then they continued to infect the next parenchymatous cells,some even infected to xylem.In the infected cells,the damages to the tissues included cell wall lignification thickening,cell deformation and plasmolysis,membranes disruption,organelles and starch grains disintegration.The growth and proliferation of the fungi inhibited the growth of cells.4.The surface structure of healthy and diseased roots of Astragalus membranaceus were researched by SEM. The results showed that there were great differences in the surface microstructure of the healthy and diseased roots.Many fungal hyphae and conidiospore in the surface of diseased roots, surface was rough, cell disorderly and cell wall was incomplete. Some concave, fracture and cavity in the surface of the root in the late infection.