Identification of quantitative trait loci for dry-matter, starch, and β-carotene content in sweetpotato

Development of orange-fleshed sweetpotatoes (OFSP) is desired for the improvement of the food supply and nutritional status of millions of people in developing countries, particularly in sub-Saharan Africa. However, sweetpotato [Ipomoea batatas (L.) Lam] breeding is challenging due to its genetic complexity, and marker-assisted breeding tools are needed to facilitate crop improvement. We identified quantitative trait loci (QTL) for dry-matter, starch, and beta-carotene content in a hexaploid sweetpotato mapping population derived from a cross between Tanzania, a white-fleshed, high dry-matter African landrace, and Beauregard, an orange-fleshed, low dry-matter sweetpotato cultivar popular in the USA. Two parental maps were constructed using a population of 240 clones. Strong correlations were observed between starch and dry-matter content (r > 0.8, P < 0.0001) in the storage roots, while moderate correlations (r = -0.6, P < 0.0001) were observed for beta-carotene and starch content. In both parental maps, QTL analysis revealed the presence of 13 QTL for storage root dry-matter content, 12 QTL for starch content, and 8 QTL for beta-carotene content. Multiple QTL regression models developed for segregation of alleles in each parent explained 15-24% of the variation in dry-matter content, 17-30% of the starch content, and 17-35% of beta-carotene content. To the best of our knowledge, this research presents the only QTL mapping study published to date for dry-matter, starch, and beta-carotene content in sweetpotato. This work improves our understanding of the inheritance of these important traits in sweetpotato, and represents a first step toward the long-term goal of developing marker-assisted breeding tools to facilitate sweetpotato breeding efforts.