Genetic linkage analysis using DNA markers in sweetpotato

Sweetpotato is one of the most important food crop species in the world, with more than 104,000,000 tons produced each year, and the breeding of superior cultivars with agronomically important traits, such as improved disease resistance, yield, and nutrient richness, is necessary, especially in developing countries. However, as a result of the crop's complex genomic architecture, which results from its hexaploidy (2n = 6× = 90), high heterozygosity, huge genome, and outcrossing nature, the analysis of genetic linkage in sweetpotato has been challenging. In addition, the lack of whole genome sequences or gene annotations for cultivated hexaploids has interrupted the validation of mapped QTL regions and gene cloning. In spite of these technical difficulties, linkage map construction and QTL mapping analysis have been reported. This review summarizes the results of these linkage analyses, which used SSR, AFLP, and retrotransposon-based molecular markers, and describes future directions for the genetic analysis and marker-assisted breeding of this important but genetically complex crop species.