title: Nuclear and chloroplast diversity and phenotypic distribution of rice (Oryza sativa L.) germplasm from the democratic people's republic of Korea (DPRK; North Korea).
abstract: BACKGROUND
  Rice accounts for 43% of staple food production in the Democratic People's Republic of Korea (DPRK). The most widely planted rice varieties were developed from a limited number of ancestral lines that were repeatedly used as parents in breeding programs. However, detailed pedigrees are not publicly available and little is known about the genetic, phenotypic, and geographical variation of DPRK varieties.
  
  
  RESULTS
  We evaluated 80 O. sativa accessions from the DPRK, consisting of 67 improved varieties and 13 landraces. Based on nuclear SSR analysis, we divide the varieties into two genetic groups: Group 1 corresponds to the temperate japonica subpopulation and represents 78.75% of the accessions, while Group 2 shares recent ancestry with indica varieties. Interestingly, members of Group 1 are less diverse than Group 2 at the nuclear level, but are more diverse at the chloroplast level. All Group 2 varieties share a single Japonica maternal-haplotype, while Group 1 varieties trace maternal ancestry to both Japonica and Indica. Phenotypically, members of Group 1 have shorter grains than Group 2, and varieties from breeding programs have thicker and wider grains than landraces. Improved varieties in Group 1 also show similar and/or better levels of cold tolerance for most traits, except for spikelet number per panicle. Finally, geographic analysis demonstrates that the majority of genetic variation is located within regions that have the most intensive rice cultivation, including the Western territories near the capital city Pyungyang. This is consistent with the conscious and highly centralized role of human selection in determining local dispersion patterns of rice in the DPRK.
  
  
  CONCLUSIONS
  Diversity studies of DPRK rice germplasm revealed two genetic groups. The most widely planted group has a narrow genetic base and would benefit from the introduction of new genetic variation from cold tolerant landraces, wild accessions, and/or cultivated gene pools to enhance yield potential and performance.
authors.affiliation: Department of Plant Breeding and Genetics, Cornell University, Ithaca 14853, NY, USA.
authors.forename: HyunJung
authors.initials: H
authors.lastname: Kim
authors.affiliation: Rural Development Administration (RDA), Suwon 441-707, Republic of Korea.
authors.forename: Eung Gi
authors.initials: EG
authors.lastname: Jeong
authors.affiliation: Department of Crop Science, Chungnam National University, Daejeon 305-764, Republic of Korea.
authors.forename: Sang-Nag
authors.initials: SN
authors.lastname: Ahn
authors.affiliation: Department of Plant Biology, Cornell University, Ithaca 14853, NY, USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Doyle
authors.affiliation: Department of Plant Breeding and Genetics, Cornell University, Ithaca 14853, NY, USA.
authors.forename: Namrata
authors.initials: N
authors.lastname: Singh
authors.affiliation: Department of Plant Breeding and Genetics, Cornell University, Ithaca 14853, NY, USA.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Greenberg
authors.affiliation: Rural Development Administration (RDA), Suwon 441-707, Republic of Korea.
authors.forename: Yong Jae
authors.initials: YJ
authors.lastname: Won
authors.affiliation: Department of Plant Breeding and Genetics, Cornell University, Ithaca 14853, NY, USA.
authors.forename: Susan R
authors.initials: SR
authors.lastname: McCouch
keywords: DPRK; Diversity; Germplasm; indica; temperate japonica