Genome-Wide Association Studies for Curd Induction Time in Brassica oleracea

Broccoli (Brassica oleracea var. italica) and cauliflower (B. oleracea var. botrytis) production in Taiwan has been confined in cool seasons due to heat stress. Heat-tolerance and early curding are two of major breeding aims. In this study, we aimed to uncover QTLs responsible for early curd formation by genome-wide association study (GWAS). A diversity panel of B. oleracea including 93 cauliflower, 86 broccoli and 13 kale accessions were used. The curding time were ranged 16~84 and 29~78 days in 2014 and 2015, respectively. The diverse panel was genotyped by multiplex shotgun genotyping (MSG) approach. A total of 220,042,148 raw reads were generated; 52,778 polymorphic SNP loci were discovered using TASSEL 5 GBS pipeline; and then 14,839 SNPs were used for analysis after filtered out minor and missing genotypes. After population structure by principle component analysis, a mixed model consists of 4 PCs and kinship in were applied to identify significantly associated SNP markers by TASSEL 5. A total of 19 significant SNPs localized on all 9 chromosomes. Some of significant SNPs were found co-localized with published QTLs mapped by bi-parental mapping populations in broccoli and cauliflower, such as previously identified BoFLC genes. The results found stable QTLs across different mapping populations as well as novel SNPs responsible for curding time in B. oleracea. The further confirmation is ongoing, and the results will facilitate to promote breeding efficiency to breed broccoli and cauliflower new varieties with early curding formation by marker-assisted selection.

Keywords: Brassica oleracea; Multiplexed shotgun genotyping, curd induction time, Quantitative trait loci, Marker assisted breeding.