Genome-Wide Association Mapping of Flowering Time in Brassica rapa

Brassica rapa is a species widely cultivated as oil and vegetable crops. Flowering time considerably impacts the economic yield in B. rapa crops. Pre-mature bolting caused by the low temperature in the early stage of plant growing results in completely loss of economic value in leafy B. rapa vegetables. To identify the polymorphisms and better understand the genetic architecture of flowering time in B. rapa, we conducted GWAS in a natural B. rapa population consisting of 688 accessions with 1.3 million identified SNPs. We identified 16 loci for bolting time and 20 loci for flowering time respectively, by analyzing phenotype data from three trails conducted in greenhouse or in open field. Candidate genes with known function or Arabidopsis orthologs were proposed, including genes that have been reported to play important roles in transition from vegetative stage to reproductive stage, including BrFLC1, orthologues of FT, VRNI. Loci without Arabidopsis orthologues were also identified which may indicate that the different regulation mechanimsms involved in B. rapa flowering control. This study enriches our knowledge of the genetic basis underlying flowering time variation in B. rapa and provides valuable markers for molecular breeding of B. rapa.