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Studies On The Oringin Of Genetic Diversity In Malus Toringoides

Posted on:2003-08-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:H P DengFull Text:PDF
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Malus Miller, belongs to sub-family Maloidae of Rosaceae in plant taxonomy. There are thirty to thirty-five recognized species of this genus in the world, which are mainly distributed in Asia, Europe and North America. Among them twenty to twenty-three, were found in China. If the eight new species published in recent years were included, there are thirty-one Malus species in China. They cover geographically all the twenty-nine provinces, municipalities and autonomous regions of china with one of exception of Hainan Province. The most densely populated areas are Sichuan > Yunnan and Shanxi Province, Which have 24, 17 and 15 species respectively. The most widespread species is Malus hupehensis(Pamp.) Rehd., whose distribution covers 17 Provinces, municoplalities and autonomous regions. The next is Malus setok Vass., whose distribution covers 15 provinces. The altitude variation of the distribution of the different Malus species in China reaches nearly 4000 meters, and they grow on various types of soil, even on desert, alkaline soil and on overhanging rocks and steep cliffs.In the past several decades, all kinds of research work have been carried out on the genetic resources of genus Malus species. Therefore, much progress has been made concerning the studies of the number of species, geographical distribution, morphology, classification, cytology, cell biology, reproductive biology and resistance characters to various environmental stresses. There are, however, many problems which need to be solved in the future work. For example, concerning the subjects of researches we've ignored grently the connection between the basic researches andapplication study. In-depth researches on the rare gene materials such as Mains toringoides are badly needed. The researches on genetic materials conservation, identification and utilization of the apple resources using the modern molecular technology are almost a blank. Biodiversity in addition has become a hot point of recent study. Many researches on species diversity of Mains Millerwere reported, the studies on genetic diversity were rarely reported, especially for the species such as Malus toringoides Hughes, which is rich in morphological and genetic diversity. In the main area populated by Malus toringoides Hughes, Malus kansuensis and (or) Malus transitoria were found occasionally. The fact of the three species' convergence in Western Sichuan and Southern Gansu shows their close relation-ships geographically. Their different distribution indicate their geographical replacements, of subflora forest vegetation of China-Himalayas,in which many new and old species co-existed.The existing experimental results show that Malus toringoides distributed widely in different area which has great altitude variation and complicated microhabitats. The root system of Malus toringoides is so developed that it can grow on prior soil and in cracks of rock. Like Malus transitoria, Malus toringoides tolerant to draught and can grow on sunny dry slope, rocks of steep cliffs, barren stone area, roadsides and field sides. Malus toringoides was also adapted to habitat shade and can grow normally gorges of hill, and even on sides of brook and river, where water often attack on. These characters are similar to Malus kansuensis. In addition, M. toringoides has complex morphological variation and a series of variants were found between Malus kansuensis and Mains transitoria. Furthermore, it has features of asexual apomixia and a good grafting affinity to many cultivars with effects of dwarfing, early fruiting and fruit quality improving on the grafted trees. So it can be a perfect apple rootstock in terms of its overall characteristics. Concerning M. toringoides there are, however, many questions, such as the molecular basis of its excellentcharacters, the genetic structure and diversity of its populations, still needed to be answered. Therefore, in this thesis the M. toringoides were selected as experimental materials. Using the metheds of flora geography N numerical taxonomy...
Keywords/Search Tags:Malus toringoides, genetic diversity, oringin, introgression hybrid, AFLP
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