title: Marker-assisted breeding of the rice restorer line Wanhui 6725 for disease resistance, submergence tolerance and aromatic fragrance.
abstract: BACKGROUND
  Rice is a staple food crop in the world. With the increase in world population and economic development, farmers need to produce more rice in limited field. However, the rice production is frequently affected by biotic and abiotic stresses. The use of natural disease resistance and stress tolerance through genetic breeding is the most efficient and economical way to combat or acclimate to these stresses. In addition, rice with aromatic fragrance can significantly increase market value for its good grain quality. Mianhui 725 (MH725) is an elite restorer line that has been widely used to produce three-line hybrid rice in China. We previously introduced rice bacterial blight resistance genes Xa4 and Xa21 into MH725 and obtained an introgression rice line Wanhui 421 (WH421), which theoretically possesses 96.9% genetic background of MH725.
  
  
  RESULTS
  Here we report the introduction and pyramiding of disease resistance genes Xa27 and Pi9, submergence tolerance gene Sub1A and aromatic fragrance gene badh2.1 in WH421 through backcrossing and marker-assisted selection. The newly developed introgression rice line was designated as Wanhui 6725 (WH6725), which theoretically possesses 95.0% genetic background of MH725. WH6725 and its hybrid rice conferred disease resistance to both blast and bacterial blight diseases and showed tolerance to submergence for over 14 days without significant loss of viability. Compared with non-aromatic rice MH725, WH6725 has strong aromatic fragrance. The major important agronomic traits and grain quality of WH6725 and its hybrid rice obtained in field trials were similar to those of MH725 and the control hybrid rice, indicating that WH6725 is as good as MH725 when it is used as a restorer line for three-line hybrid rice production.
  
  
  CONCLUSIONS
  We have successfully developed a new restorer line WH6725 with disease resistance to rice blast and bacterial blight, tolerance to submergence and aromatic fragrance, which can be used to replace MH725 for hybrid rice production.
authors.affiliation: Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore, 117604, Republic of Singapore.|Key Laboratory of Rice Genetics and Breeding, Anhui Rice Research Institute, Anhui Academy of Agricultural Sciences, Hefei, 230031, China.
authors.forename: Yanchang
authors.initials: Y
authors.lastname: Luo
authors.affiliation: Key Laboratory of Rice Genetics and Breeding, Anhui Rice Research Institute, Anhui Academy of Agricultural Sciences, Hefei, 230031, China.
authors.forename: Tingchen
authors.initials: T
authors.lastname: Ma
authors.affiliation: Plant Protection Research Institute, Anhui Academy of Agricultural Sciences, Hefei , 230031, , China.
authors.forename: Aifang
authors.initials: A
authors.lastname: Zhang
authors.affiliation: Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore, 117604, Republic of Singapore.
authors.forename: Kar Hui
authors.initials: KH
authors.lastname: Ong
authors.affiliation: Key Laboratory of Rice Genetics and Breeding, Anhui Rice Research Institute, Anhui Academy of Agricultural Sciences, Hefei, 230031, China.
authors.forename: Zefu
authors.initials: Z
authors.lastname: Li
authors.affiliation: Key Laboratory of Rice Genetics and Breeding, Anhui Rice Research Institute, Anhui Academy of Agricultural Sciences, Hefei, 230031, China.
authors.forename: Jianbo
authors.initials: J
authors.lastname: Yang
authors.affiliation: Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore, 117604, Republic of Singapore. yinzc@tll.org.sg.|Department of Biological Sciences, 14 Science Drive, National University of Singapore, Singapore, 117543, Republic of Singapore. yinzc@tll.org.sg.
authors.forename: Zhongchao
authors.identifier: http://orcid.org/0000-0001-8519-5879
authors.initials: Z
authors.lastname: Yin
keywords: Marker-assisted selection; Mianhui 725; Pi9; Sub1A; Wanhui 6725; Xa21; Xa27; Xa4; badh2.1