| Sect. Thea (L.) Dyer was a section in the genus Camellia L., Theaceae. Excluding tea plant (C. sinensis), which was a widely spread species both in China and the world, it was centralized distributed in the south and southwest China. This was an important section in Camellia. Tea plant was the most important cash crop in the section. In this dissertation, a novel genomic DNA isolation method, the genetic polymorphism and molecular discrimination of tea plant, the molecular and morphological systematics of section Thea were systematically investigated. The followings were main results.1. The isolation of genomic DNA was the first step of molecular markers research. A SDS-iso-propanol method suitable for tea plant, which was plentiful of tea polyphenols, had been developed using a modification of Chen Darning's method from different sample storage conditions such as fresh, dry and frozen shoots. It was a quick, easy, economical and effective method. The tactics were as follows: Before the cell nuclear membranes were decomposed, the tea polyphenols and proteins etc.were removed. This step was critical for preventing polyphenol to be oxidized into quinone. Then the nucleuses were splitted by SDS, DNA was precipitated by iso-propanol or alcohol. The average DNA yields were 527 u g/g with fresh base. The DNA quality was fresh > dry ones; stored in liquid N2>in -20 癈. All of them were suitable for RAPD and RFLP analyses. The successful use of silica to dry tea shoots was meaningful for wild fields and long-distance sample collection.2. Twenty primers, which could amplify polymorphism in 15 Chinese tea clonal germplasms, were selected from 100 arbitrary 10-mer primers. A total of 1050 loci with an average 52.5 loci per primer and 70 loci per germplasm were amplified. In the total 137 amplified bands, 129 were polymorphic, corresponding to 94.2%. The genetic distances were 0.16 to 0.62, on average 0.37. The genetic polymorphism and distance were much higher and wider than those of Kenya, South Korea and Japan. The polymorphic frequency was between 0.07 and 0.93, on an average of 0.47. Primer 201 was the lowest, average 0.24; meanwhile, S207 average 0.83, the highest. The result of UPGMA grouped the 15 tea germplasms into 3 groups. The intra-group and inter-group relationship was analyzed.3. The discrimination of 24 wild tea germplasm resources using DNA markers was conducted. The result showed that RAPD marker was a very effective tool and robust method in tea germplasm discrimination. There were 3 independent ways to identify the tea germplasms, a) unique RAPD markers, b) unique band patterns and c) a combination of the band patterns provided by different primers. The presence of 15 unique RAPD markers and the absence of 3 unique markers obtained from 12 primers made it possible to identify 14 tea germplasms. Using the unique band patterns of primer OPO-13 could identify 10 tea germplasms. 15, 17 and 20 germplasms could be identified using the band patterns combination of two or three primers, respectively. It was of much importance using minimum primers to obtain the maximum discrimination capacity. All the 24 tea germplasms could be entirely discriminated by the band patterns combination of primer OPO-13, OPO-12, OPG-18 and OPA-13, including two wild teaplants of very similar morphological characteristics and chemical components.4. The genetic polymorphism and molecular systematics of 24 species and varietiesin section Thea were investigated. Fifteen arbitrary 10-mer primers were selected from the 61 screened. A total of 102 polymorphic bands (6.8 polymorphisms/ primer) out of 107 reproducible products (7.1 fragments/primer) were amplified from the selected 15 primers, corresponding to 95.3% polymorphism of the amplification bands. The relative polymorphic frequency ranged from 0.04 to 0.96. However, the general relative frequency of polymorphic was low with an average of 0.30, varying from 0.16 to 0.60. Molecular phylogenetic dendrogram of section Thea was constructed using UPGMA a...
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