Studies On The Causal Factors And Mechanism Of Ginkgo Chlorosis

Ginkgo biloba L. is a kind of common steet-tree in cities.In recent years, many Ginkgoes have a widespread and serious chlorosis in Dalian. In this thesis,the causal factors and the disease index are investigated.We analyze the activities of defensive enzymes,conductivity , endophyte categories and its number to find the causal factors and the chlorosis mechanism to provide the foundation to the garden department to repair,prevent and cure this disease.In the survey, the incidence of this diease is 91.2%, disease index is 89.52(data 2006),Ganjingzi Section is the most serious area in Dalian. Observing the infected leaf-structure by the electromicroscope ,there are not phytoplasma,virus or other disease microorganisms, therefore we conclude that Ginkgo chlorosis in Dalian is not infective disease.According to the soil heavy-metal content,pH value,the content of SO2 and NOx,we consider that there are many reasons to cause this disease,including environment,damages from both human and physiology,weak adaptability of itself,etc.Amony these cases,the soil pH value is 7.8 ,which is beyond the most suitable pH range of Ginkgoes ask for(6.5-7.5) ;the Cd content (1.0mg/kg )in soil is on the edge of plant to grow normally(GB15618-1995), it might be the main reason to cause this disease. In addition,content of SO2 and NOx in the air make the plants chronic injury, damage their cells ,cell saps extravasate heavily , conductivity increases, the activity of the POD, PAL and PPO decreases which could lead the resistance ability decline.Purifying the infected and healthy Ginkgo leaves, there are 5 categroies endophyte.3 categroies bacteria are Enterococcus faecalis ,Enterococcus faecium, Streptococcus uberis;2 categroies fungi are Penicillium brevicompactum, Cladosporium sphaerospermu.Although the endophyte categroies are little differences between them, their numbers are different notability,the endophyte number of infected plant is 1.5x105/ml and the endophyte number of healthy plant is 3.5x106 /ml ,which is 23 times of the infected.The volatile matter of Ginkgo leaves have good effectiveness of bacteriostasis.Comparison of the antibacterial activity to Escherichia coli and Staphylococcus aureus Rosenbach amony 31 plants , effect of Ginkgo is remarkable, the antibacterial activities are 23%,30%. leaves from different time have different effects to bacteriostasis,such as Ginkgo little leaf,new leaf,grown leaf,their antibacterial ratio are 17%,25%,23% to Escherichia coli and 21%,20%,30% to Staphylococcus aureus Rosenbach.The suggestion to the garden department is that we should choose Ginkgo,Magnolia grandiflora,Chinar,Juglans regia,Sytinga microphylla,etc as virescence trees ,which will be benefit to construct eco-city and eco-community.