Assessing genetic diversity in Vietnam tea - Camellia sinensis (L.) O. Kuntze using morphology, inter-simple sequence repeat (ISSR) and microsatellite (SSR) markers

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Assessing genetic diversity in Vietnam tea [Camellia sinensis (L.) O. Kuntze] using morphology, inter-simple sequence repeat (ISSR) and microsatellite (SSR) markers
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 Goettingen University, Germany, Nông nghiệp, , 2007 ;
 Tác giả   Võ Thái Dân
 Người hướng dẫn   Prof. Heiko C. Becker & Prof.Reiner Finkeldey
 Từ khóa   Tiến sỹ
  DOI luận án quốc tế DOI   [ URL]  [chưa có PDF]

Tiếng Anh

Tea (Camellia sinensis (L.) O. Kuntze) is probably the most important beverage worldwide and gains further popularity as an important ‘health drink’. It is served as daily morning drink for two third of the world population. Although demand of tea increases yearly, the available land for tea cultivation is limited and an increasing productivity with reduced production costs is required. Therefore, tea breeding will be of increasing importance.

Known as a cross pollinated plant, tea can not be separated into discrete groups to identify various taxa. Since hybridization is used and clonal propagation is recommended, the widespread cultivation of clonal tea can diminish genetic diversity if care is not taken to use clones of dispersed origin. Information on taxonomic characteristics, genetic diversity and biogeography of tea in the living collections may help in identifying genotypes with high production potential which could be used as genetics resources to improve the commercially grown tea.

With a longstanding history of cultivating and consuming tea, Vietnam is believed to be highly rich in genetic diversity of tea. The main objectives of this study are: (1) assessing the morphological diversity of tea grown at Lam Dong province – the main tea producing province of Vietnam; (2) collecting accessions of wild giant shan tea, local tea, selected/improved tea, and imported tea to assess the genetic diversity on molecular level by using inter simple sequence repeat (ISSR) and simple sequence repeat (SSR) markers. This will help to identify parents for hybridization and to reduce the number of accessions needed to maintain a broad range of genetic variability.

In Chapter 1, the background of this study is reviewed, i.e., the main properties and types of molecular markers presently used; an overview of tea biology and the world tea production; the recent advances of assessing tea diversity; and tea production and research in Vietnam. Vietnam is one of the top producing tea countries, but tea yield is still lower than the world average. Tea production has an important role in the agriculture sector, particularly at the highlands and the mountainous areas.

Chapter 2 reports the genetic diversity of 31 tea accessions which are commercially planted or new promising selections in Lam Dong province based on 34 quantitative and qualitative morphological characteristics. The stem, the 4th leaf, young shoot and flower were described following the IPGRI’s guidelines. UPGMA-derived dendrogram and principal co-ordinates (PCo) plot were produced based on Euclidean distances for 16 quantitative morphological data. Results showed the high diversity of Lam Dong tea. All tested accessions clustered into 4 groups and all known China, India and Shan teas were clearly separated in sub-groups. The results of this study generally meet with the reputed taxa currently accepted in local tea production.

The assessment of genetic diversity in Vietnam tea using molecular markers is presented in chapters 3 and 4. In chapter 3, 144 tea accessions growing in Vietnam were screened by inter-simple sequence repeat (ISSR) markers to reveal the genetic diversity at molecular level. Genomic DNAs of all 144 accessions were extracted and primarily checked by 3 RAPD markers. Due to the low quality of DNAs, only 71 accessions were used in the study. The data were statistical exploited via cluster analysis based on Dice similarity coefficient matrix and AMOVA analysis. Among 15 ISSR primer tested, only 7 primers generated 64 polymorphic bands. The number of polymorphic bands generated by a primer varied between 2 and 16 and the size of the polymorphic amplified fragments scored ranged from around 325 to 2500 bp. Estimated Dice similarity values ranged from 0.09, between the most distant accessions LD97 BL (selected tea) and Yabukita (imported tea), to 1.00, between the most similar accessions Chat Tien (local tea) and Suoi Giang 6 (wild giant tea). The tested accessions exhibited more variation than in earlier reports. This great variation may be attributed to the wide variability in origin of the tested accessions. Except for some accessions remaining distinct and ungrouped, at about 50% similarity level, the dendrogram using UPGMA formed 4 clusters. The results showed the high variation between and within local, wild, selected and imported accessions.

When using simple sequence repeat (SSR) markers (chapter 4), 6 out of 17 primer pairs detected 115 different alleles from 69 accessions. The number of alleles per SSR marker varied from 11 to 25. The expected heterozygosity was very high, ranging from 0.703 to 0.928. 326 pairs of accessions had no alleles in common. The maximum value of estimated similarity was 0.95, between the most similar accessions F16 (selected tea) and Ho Nam 1 (imported tea). Cluster and AMOVA analysis showed the high variation between and within local, wild, selected and imported accessions.

For 51 accessions, results from both ISSR and SSR markers are available (chapter 5). A total of 180 polymorphic bands were generated with 7 ISSR and 6 SSR markers. UPGMA-derived dendrogram, bootstrap values and the PCo plot all showed that there could no clear cluster be identified. At the value of 0.39 of Dice similarity coefficient, except for some accessions remaining distinct and ungroup, 25 accessions of wild giant, local, selected and imported tea were all grouped into one large cluster; the others were clustered into 3 small groups. In each cluster, some sub-groups agreed with the known taxonomy system. However the results also showed some differences to the conventional taxonomy system.

Although no clearly distinct clusters could be identified, in general the results met the conventional classification (with some exception). The variations between and within local, wild, selected and imported accessions were very high due to the wide range of origin of the tested accessions. The wild giant accessions are not clearly separated from the other ones because tea is freely cross pollinated and there have been many introgressions from genetic resources of wild giant tea into cultivated tea.

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