| Cotinus coggygria Scop., famous scenery afforestation trees of Xiangshan mountain in Beijing, plays important role in ecological environment construction of Beijing. In recent years, because of lacking effective control measure, the withered death of the trees severely happened. This kind of disease not only destroys local scenery resources, but also leads to a serious impact on Beijing's urban landscape environment construction. This paper had systematically studied the pathogenicity and biological characters of Verticillium dahliae causing Cotinus coggygria wilt, the pathogen community from root area in health and infected Cotinus coggygria, the dynamic change of electronic index in tree stem inoculated with dominant strain of Verticillium and the bilological characters of toxin of pathogen. All these research contents were provided the fundamental information to understand the mechanism of Cotinus coggygria Verticillium wilt and biological control to this disease. The main results of this paper were as follows:1 The pathogen of Cotinus coggygria Verticillium wilt was V.dahliae through the identification of morphological and molecular biology. It had different colony shapes. The mycelia grew best on PDA culture.The death temperature of conidium was probably 45℃, The optimum temperature of conidium growth was 25℃~30℃. The best utilization of carbon was usage of glucose, maltose and amylum. Potassium nitrate was the best way to utilize nitrogen and ammonium nitrogen inhibited the colony growth.2 The community composition, the amount and the dynamic changes related to season from root area of C. coggygria Verticillium wilt were analyzed. The results showed that C. coggygria Verticillium wilt root fungus community composition was diverse during different seasons. The dominant species included V. dahliae, Fusarium spp., Oidiodendron sp., Cylindrosporium sp., Gliocladium sp. etc. But frequency of these species varied in different seasons. V. dahliae was dominant species during May and June, and isolation frequency could reach 100% in the period.3 The disease did not happen in C. coggygria after inoculating with Fusarium spp. and Cylindrosporium spp., respectively. Inoculating with three strains of V. dahliae, the pathogenicity were 60%, 70%, 90%, respectively; However, after inoculating with the mixture of V. dahliae and Fusarium spp., the pathogenicity was 100 %. Re-separate different parts of Cotinus coggygria wilt including root, stem and leaf, V. dahliae strains almost 61.7%. V. dahliae strains from wilt leaves were 96.97% of total fungal strains.In order to better understanding the dynamic change of C. coggygria stem capacitance and impedance after inoculating with different fungal strains, the paper also studied the electrical indexes of tree stem after inoculating with different fungal strains. The results indicated that tree stem impedance increased gradually, but the tree stem capacitance and unit capacitance decreased with the development of the process of infection after inoculating with V. dahliae. The test also found that both healthy tree and diseased tree, the stem capacitance had significant negative correlations with the distance between the electrodes and significant positive correlations in the stem impedance, and the stem capacitance had significant positive correlations with DBH (diameter at breast height).4 The microstructure and distribution of pathogen fungi in C. coggygria Verticillium wilt root were studied by permanent paraffin sectioning and microscope photograph. The result showed that pathogenicity of V. dahliae strains from different regions was not obvious to one-year-old C. coggygria seedlings. With the increase of the inoculation days, the invading hyphae, mahogany substance, gluey material, etc. can be observed in the root vessels of C. coggygria.The filling substance existed in some cells of xylem elements vessels in the roots. With the increase of inoculation days, the number of vessel that was infected by mycelium, gluey material etc. and resin duct exudates of the secondary phloem gradually increased.5 Acording to a series of tests about biological activities from the crude toxin of wilt pathogens, it could conclude that the V. dahliae crude toxin had virulence on radicel, in vitro twig, in vitro leaf and living seedling. Meanwhile, the experiment indicated that crude toxin after high-temperature treatment had no significant negative effect on the testing-hosts.6 Endophytic fungus that were isolated from healthy C. coggygria roots from different regions with conventional isolation method were surveyed.Results indicated that there were thirty-three strains of endophytic fungi, and dominant species included Mycelia sterilia, Humicola and Penicillium. It also showed that quantity and species varied in healthy C. coggygria roots from different places.Antagonistic activities of endophytic fungi to V. dahliae demonstrated that Xylaria hypoxylon strain and Memnoniella strains and Candida strains showed strong activity against V. dahliae, while other strains hadn't significant antagonism to the pathogen. |
