| Praxelis clematidea, which is a kind of invasive weed, spreads throughout the South China region and causes great damage to agricultural economy, environmental ecology and biological diversity. Thus, the research on allelopathy and genetic diversity of Praxelis clematidea will help to control the invasive plant effectively and understand the evolution of Praxelis clematidea.In this study, we tested the allelopathic effects of aqueous extracts of Praxelis clematidea from different organs on seedling growth of target plants by the means of a bioassay method. The PCR reaction system of RAPD was optimized using Praxelis clematidea from different habitats of Hainan and the dendrogram for geography group genetic diversity of Hainan province were conducted.The major conclusions are shown as follows:1 The effects of Praxelis clematidea extracts from different tissues on measurements of root growth, seedling growth and freshweight of target plants were tested. The allelopathy of leaf extract was the strongest, which indicated that maybe leaves are the main organs releasing the allelochemical. Then, we found that there was facilitation and concluded that there is not a single allelochemical from Praxelis clematidea but rather a more comprehensive allelochemical profile.2 The allelopathic effects of Praxelis clematidea extracts from every tissue in different growth periods were not significant on the seedling growth of radish. The allelopathy in the vegetative growth stage was a little stronger than in the reproductive growth stage. The allelopatic effects of extracts from plants originating from many kinds of habitats indicated that Praxelis clematidea may release a larger number of diverse allelochemicals to promote its allelopathy and adapt to the conditions of severe environments.3 The PCR reaction system of RAPD was optimized. The best reaction condition was 0.5ng/μL DNA,1.0μmol/L primers,150μmol/L dNTP, 2.0mmol/L Mg2+and 1.0U Taq polymerase in a 25uL reaction system.4 Through the RAPD-PCR cluster analysis, the Hainan various cities geography group of Praxelis clematidea will divide into two class groups:Chengmai, Haikou, Wenchang, Linkao, DanZhou, Changjiang are a class group, Dongfang, Ledong, Sanya, Baoting, Wuzhishan, Qionghai, Wanning, Lingshui, Dingan are a class group, Tunchang is a class group, Baisha is a class group, Qiongzhong is a class group.5. Through the NTsys-pc2.10 data processing, analyzes the genetic similarity coefficient of each geography group of Praxelis clematidea, The genetic similarity coefficient between 0.5396825-0.9047619, majority between 0.75-0.90. The genetic variations of the species in different geographic locations is believed to be the results of rapic evolution in their intrusion process in Hainan. The principal factors contributing to the gnetic variations of Praxelis clematidea may be ascribed to temperature, rainfall and accessibility.6. The allelopathic effects is one of the important means of Praxelis clematidea for rapid establishment of its population in different locations, and the variation in their genetic similarity in different locations is the basis of their difference in allelopathic effects.The present study analysed the allelopathic potentials of different parts and different development stage of Praxelis clematidea and compared the allelopathic effects of Praxelis clematidea from different habitats. The present study also classified the genetic diversity of Praxelis clematidea various counties and cities in Hainan Island through RAPD-PCR cluster analysis. The results of the present study is of certain theorectical and practical implications for Praxelis clematidea intrusion mechanism and its control. |
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