title: The Usefulness of Known Genes/Qtls for Grain Quality Traits in an Indica Population of Diverse Breeding Lines Tested using Association Analysis.
abstract: BACKGROUND
  A number of studies reported major genes/QTLs for rice grain shapes, chalkiness and starch physicochemical properties. For these finely mapped QTLs or cloned genes to make an impact in practical breeding, it is necessary to test their effects in different genetic backgrounds. In this study, two hundred nineteen markers for 20 starch synthesis genes, 41 fine mapped grain shape and related traits QTLs/genes, and 54 chalkiness QTLs/genes plus 15 additional markers and a large indica population of 375 advanced lines were used to identify marker-trait associations under 6 environments that can be used directly in breeding for grain quality traits.
  
  
  RESULTS
  The significant associations detected by the QK model were used to declare the usefulness of the targeted genes/QTLs. A total of 65 markers were detected associations with grain quality trait at least in one environment. More phenotypic variations could be explained by haplotype than single marker, as exemplified by the starch biosynthesising genes. GBSSI was the major gene for AC and explained up to 55 % of the phenotypic variation, which also affected GC and accounted up to 11.31 % of the phenotypic variation. SSIIa was the major gene for chalkiness and explained up to 17 and 21 % of variation of DEC and PGWC, respectively. In addition, RMw513 and RM18068 were associated with DEC in 6 environments as well. Four markers (RGS1, RM15206, RMw513 and Indel1) tightly linked to GS3, gw5, and qGL7-2 were the most important ones for grain shapes. Allelic combinations between SSIIa and RMw513 revealed more variations in DEC.
  
  
  CONCLUSIONS
  The validated markers for genes/QTLs with major effects could be directly used in breeding for grain quality via marker-assisted selection. Creating desirable allelic combinations by gene pyramiding might be an effective approach for the development of high quality breeding lines in rice.
authors.affiliation: Plant Breeding, Genetics and Biotechnology Division, International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.
authors.forename: Xiangqian
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Plant Breeding, Genetics and Biotechnology Division, International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.|Present address: Longping Branch, Graduate School of Central South University, Changsha, 410125, Hunan, China.
authors.forename: Lijie
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Plant Breeding, Genetics and Biotechnology Division, International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.
authors.forename: Kimberley
authors.initials: K
authors.lastname: Ponce
authors.affiliation: Plant Breeding, Genetics and Biotechnology Division, International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines. g.ye@irri.org.
authors.forename: Guoyou
authors.initials: G
authors.lastname: Ye
keywords: Association analysis; Chalkiness; Grain quality; Rice; Starch synthesis genes