| Onion (Allium cepa L.) is an important crop which possesses many health beneficial compounds, but also presents difficulties for genetic studies (i.e. complex genome, biennial generation, and inbreeding depression). To broaden the limited genomic resources, transcriptome sequencing using the Roche-454 platform of two inbred lines (OH1 and 5225) was performed. Single nucleotide polymorphisms (SNPs) were identified (3,364 on 1,716 cDNA contigs), and were mapped using gynogenic haploid families generated from F1 plants from the cross of OH1 and 5225. The most dense map of onion to date with 597 SNPs forming ten linkage groups was constructed from this study. Three hundred and thirty nine of these new SNPs also segregated in the previously developed F2 family from BYG15-23 x AC43. These two families shared 223 SNP markers, which were used to join maps and assign linkage groups to chromosomes. A second study characterized the genetics of red-bulb color and soluble-solids contents in the OH1 x 5225 haploid families. Quantitative trait loci were identified controlling the presence and intensity of anthocyanins in bulbs. Three QTLs, one on chromosome 7 and two in repulsion phase linkage on chromosome 4, conditioned the presence of anthocyanins. The quantities of the two anthocyanins [peonidin 3-glucoside and cyanidin 3-(6"-malonoyl-laminaribioside)] were assessed using high performance liquid chromatography (HPLC). Significant QTLs on chromosome 1 and 8 were associated with concentrations of peonidin 3-glucoside, while QTLs on chromosome 1 and 4 were associated with cyanidin 3-(6"-malonoyl-laminaribioside) concentrations. Significant correlations between the two anthocyanin concentrations and visual scores were detected. Consistent with previous studies, soluble-solids content 30-days postharvest was significantly associated with a region on chromosome 5. Genetic variation was discovered in yellow onion that contributed to increasing the intensity of red-bulb color in progenies. |
