Genetic Diversity And Fingerprinting Of Chinese Improved Tea Cultivars

The tea plant is one of the important cash crops in China. A lot of tea cultivars with excellent characteristics have been bred in recent years. On the one hand, due to the samilar breeding strategy and backbone parents of those tea cultivars, the genetic relationship becomes closer and genetic background becomes narrower. Revealing the genetic relationship and structure of these tea cultivars on molecular level would provide scientific instruction for parental selection for hybridization breeding program. On the other hand, more and more new cultivars are bred and higher demand for tea plant discrimination was proposed. By the advantage of convenience, promptness and stability, SSR(simple sequence repeat) fingerprinting identification technique is quite suitable for cultivar identification. In this study, we analysed the genetic diversity and estabilished the molecular fingerprinting by core markers of 254 tea cultivars using 185 SSR markers selected from tea plant genetic linkage map. The main results are as follows:1. After the initial screening, 128 SSR markers with clear and stable amplification bands were obtained. The average number of alleles, genotypes, polymorphism information content(PIC) had great difference on different linkage groups. According to convenient degree of amplification bands statistic, PIC and genotype number, 2 sets of core primers distributed evenly in the 15 linkage groups were screened. The theoretical probability that any two cultivars had identical SSR genotypes was 6.0×10-13. Meanwhile, a minimum of 30 SSR primers are necessary for proper analysis of the genetic diversity of 254 tea cultivars.2. A total of 128 SSR markers were subjected to amplified 254 tea cultivars, 629 alleles were detected. The average observed heterozygosity was 0.43, expected heterozygosity was 0.54, Shannon’s information index was 1.03, PIC was 0.5, gene diversity was 0.54, respectively. From the geographic area, the gene diversity of Yunnan, Guangdong, and Chongqing was the highest, all more than 0.5; Taiwan was lowest, only 0.29. For the gene diversity of different period bred cultivars, the 2000 s was the highest(0.54), next were 1990 s, 2010 s and 1980 s. The genetic distance was 0.32 in 1990 s, then decreased steadily in recent years. The 254 tea cultivars were classified into three groups by N-J method based on genetic distance, and were grouped into five populations by structure analysis based on mathematic simulation.3. A total of 30 core markers were used to amplify the same 254 tea cultivars by capillary electrophoresis(CE) fluorescence labeling and polyacrylamide gel electrophoresis(PAGE) silver detection technology, respectively. CE detected more 63 allele variation, 2 average alleles and 7 genotypes at each locus than PAGE. PIC and PD(power of discrimination) value of CE were also higher. CE fluorescence labeling test can directly and accurately obtain the exact size of target DNA fragments. The fingerprinting of 254 tea cultivars by the prioritized set of primers is constructed by translating the CE fragment size data into a genotype format.