title: Design of a Brassica rapa core collection for association mapping studies.
abstract: A Brassica rapa collection of 239 accessions, based on two core collections representing different morphotypes from different geographical origins, is presented and its use for association mapping is illustrated for flowering time. We analyzed phenotypic variation of leaf and seed pod traits, plant architecture, and flowering time using data collected from three field experiments and evaluated the genetic diversity with a set of SSR markers. The Wageningen University and Research Centre (WUR) and the Vavilov Research Institute of Plant Industry (VIR) core collections had similar representations of most morphotypes, as illustrated by the phenotypic and genetic variation within these groups. The analysis of population structure revealed five subgroups in the collection, whereas previous studies of the WUR core collection indicated four subgroups; the fifth group identified consisted mainly of oil accessions from the VIR core collection, winter oils from Pakistan, and a number of other types. A very small group of summer oils is described, that is not related to other oil accessions. A candidate gene approach was chosen for association mapping of flowering time with a BrFLC1 biallelic CAPS marker and a BrFLC2 multiallelic SSR marker. The two markers were significantly associated with flowering time, but their effects were confined to certain morphotypes and (or) alleles. Based on these results, we discuss the optimal design for an association mapping population and the need to fix the heterogeneous accessions to facilitate phenotyping and genotyping.
authors.affiliation: Laboratory of plant breeding, Wageningen University, 6700 AJ, Wageningen, The Netherlands.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Zhao
authors.forename: Anna
authors.initials: A
authors.lastname: Artemyeva
authors.forename: Dunia Pino
authors.initials: DP
authors.lastname: Del Carpio
authors.forename: Ram Kumar
authors.initials: RK
authors.lastname: Basnet
authors.forename: Ningwen
authors.initials: N
authors.lastname: Zhang
authors.forename: Jie
authors.initials: J
authors.lastname: Gao
authors.forename: Fei
authors.initials: F
authors.lastname: Li
authors.forename: Johan
authors.initials: J
authors.lastname: Bucher
authors.forename: Xiaowu
authors.initials: X
authors.lastname: Wang
authors.forename: Richard G F
authors.initials: RG
authors.lastname: Visser
authors.forename: Guusje
authors.initials: G
authors.lastname: Bonnema
mesh_terms: D000483:Alleles; D029741:Brassica rapa / Q000235:genetics*; D002874:Chromosome Mapping / Q000379:methods*; D032461:Chromosomes, Plant / Q000235:genetics; D035264:Flowers / Q000235:genetics; D056726:Genetic Association Studies; D014644:Genetic Variation; D005838:Genotype; D006238:Haploidy; D010641:Phenotype; D040641:Quantitative Trait Loci