Genetic Diversity of Taiwan Landrace and Cultivars of Rice (Oryza sativa L.)

• Main Authors: Su-Huang Chang, 張素凰
• Other Authors: Yann-Rong Lin
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/62538799127557121405

碩士 === 國立臺灣大學 === 農藝學研究所 === 99 === Rice is one of the most important cereal crops in the world which supplies the 23% calorie for human. Asian cultivated species, Oryza sativa, is classified in the family Poaceae and genus Oryza and includes two sub-species, indica and japonica. The distinct characteristics of indica and japonica could be observed, which were gradually diversified during the evolution of rice under natural selection and domestication. Some traits related to the yield or growth habitat of the rice, such as shattering and dormancy, would be selected against. Wild rice would be domesticated into landraces through these processes. Landraces were selected strictly by breeders in modern breeding process in order to establish cultivars for specific breeding goals. As the result, the genetic diversity of the modern cultivars is relatively smaller than those of landrace and wild rice. Nowadays, climate changes because of global warming increase the frequencies of extreme weather, such as drought and floods. This would also lead to the change of pathogens’ and insects’ living habit, which influence the growth and yield of modern cultivars because of their narrow gene pool. Landraces enriched genetic resources could possess resistance and tolerance to abiotic and biotic stresses. Landraces are useful germplasm to improve genetic diversity of modern cultivars. It would be better to account phylogenetic relationship before employ of landraces to breeding program. We used 75 markers subjected by high resolution capillary electrophoresis to genotype 83 landraces, 53 modern cultivars, and 12 wild rice which were collected from Taiwan, Japan, China and other Asian countries. Sixty six (88%) markers were displayed high polymorphism with PIC (Polymorphic Information Content) larger than 0.5, and seven markers were detected at least 26 alleles with estimated PIC larger than 0.9. All the highly polymorphic markers uncovered in this study could be applied to linkage analysis, and the alleles specific to varieties could be used for variety identification. In order to infer population structure, software structure conducted by model-based clustering method could be separated 148 accessions into 5 subpopulations, including indica cultivars, indica landraces, japonica cultivars, japonica landraces, and wild rice. There were great genetic differentiation among subpopulations (Fst>0.15), except indica landraces and wild rice. In spite of the fact that mentioned above, the gene diversity of wild rice (0.74) is still higher than of indica landraces (0.58). According to PCoA (Principle Coordinate Analysis), all accessions were grouped to two groups corresponding to indica and japonica. The genetic distances were closer among cultivars than among landraces, indicating that cultivars had more similar genetic background. The distribution of landraces and wild rice were sparse, indicating little similarity and high variation. The 148 accessions were separated into two distinct groups, indica and japonica, by Neighbor-joining phylogenetic tree, which is a distance-based clustering method. There are variations between accessions in both groups, which could be subdivided into 12 groups at least. Furthermore, modern cultivars and landraces can be subdivided into different groups which could imply a certain genetic distance. The average alleles number of every marker, PIC and genetic diversity among indica, was 8.31, 0.58, 0.61, respectively. Also in japonicas there were 7.05, 0.55, and 0.59, respec of indica tively. The genetic diversity of indica was expected to higher than of japonica. The Fst between indica and japonica was 0.31, which was higher than the threshold 0.25, implying the genomes of indica are highly differentiated from japonica. In the year of 1981, the government of Taiwan changed the breeding objective from yield to rice quality, which separated the cultivars in Taiwan into two stages, early stage and late stage. The genetic diversity of 7 indica cultivars in early stage and 12 in late stage were 0.52 and 0.51, respectively. Fst of indica cultivars between two stages was less 0.05, indicating no difference genetic diversity of parents used in indica breeding programs. On the other hand, the genetic diversity of japonica cultivars in early stage (n=3) and late stage (n=25) were 0.29 and 0.42, respectively. Fst of japonica cultivars was 0.38 between early and late stage. It indicated that there is a variation among the breeding parents of japonica cultivars during the breeding process. However, the large difference in sample size leading to bias estimation of genetic diversity could not be ruled out. This study suitably estimates the rice genetic resources by analyzing the phylogenetic relationship, subpopulation structure, and genetic diversity among 148 accessions. It could provide suggestions to improve cultivars in different requests and increase the genetic variation simultaneously.