| The outburst of root rot disease is one of the main reasons for a heavy yield loss among a wide range of agriculturally important crops, economic plants as well as ornamental flowers across the world. In China, there are more than 20 species of cultivated plants, of which the underground parts are normally processed to be remedies used in traditional Chinese medicine therapies, haunted by this disease. One of these plants is Chuanxiong (Ligusticum chuanxiong Hort.), the top-renowned genuine medicinal herb produced in Sichuan Province, which is known for its remarkable efficacy of activating blood, promoting Qi, dispelling wind and relieving pain. Since root rot disease has become a common complain in the cultivation cycle of Chuanxiong, and hitherto there is no pragmatically effective measures to control it, this disease has become a highlight of research. As etiological research is the beginning steps for further in-depth exploration, this thesis focuses on the identification of causal agents of root rot disease in Chuanxiong, and it is hopeful to pave the way for the comprehensive management of this disease in the field.Firstly, the symptoms on Chuanxiong plants with root rot disease were observed and recorded; and correspondingly, the grading system of this disease built. The root rot occurred occasionally during January to February, and then the incidence increased sharply between April and May, and the muggy days in May trigger the peak of root rot incidence. At the early stage of the disease, the vascular bundles in the basal part of aerial stems, fibrous roots turn brown, and brown spots are likely to be seen in the inner side of rhizomes. With the progressing of the disease, the injured area expands. Ulceration on the fibrous root and rhizome appears, which would lead to the fall off, decay or paste, while the symptoms on the aboveground parts are always without significance. Therefore, the scale of this disease has been divided into 5 levels based on the browning area of the rhizome.Then, an investigation of the incidence of the disease has been carried out span the district of Dujiangyan and Pengzhou City (in Sichuan Procince) from April to May, 2015. Consequently, infected plants could be found in all those fields surveyed, and the incidence in Dujiangyan (44.8%) was remarkably higher than the figure in Pengzhou (20.2%). P<0.01; Also, a higher disease index (23.13) was displayed in the record of Dujiangyan, while the index for Pengzhou was 12.81, P=0.98>0.05.After that, the rhizome of Chuanxiong with typical symptoms of root rot disease was collected to analyze the causal agents. The whole experimental procedure was designed according to Koch's postulates, and as a result,4 fungal isolates showed the pathogenicity under both in vitro and in planta inoculation trials, and all of them could be re-isolated from the infected Chuanxiong rhizome 14 days after inoculating. Among all these pathogens, strain f4-19 showed the strongest virulence. Also, fibrous roots with stab wounds showed significantly higher susceptibility to this disease (P=0.015<0.05).Finally, methods of morphology and molecular biology were both applied to the identification of pathogenic fungi, and consequently strain f2-16. f 3-2, f4-19 and f5-7 were identified as Fusarium solani, Plectosphaerella cucumerina. F. oxysporum and Phoma glomerata respectively, among which species Plectosphaerella cucumerina and Phoma glomerata were reported for the first time to cause root rot disease on Chuanxiong to the knowledge of the author. The Genbank accession number for these pathogens are KJ573076, KJ573077, KJ573079 and KJ573081. |
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