High-Density Linkage Map Construction for Identifying Gene(s) Associated with Soil Rot Resistance in Sweetpotato

Sweetpotato [Ipomoea batatas (L.) Lam)] is one of the most important crop species in the world with more than 104,000,000 tons in annual production (FAO). Owing to its carbohydrate content and yield, this crop is a vital source of nutrient especially in developing countries. Streptomyces ipomoea is the causative agent of a destructive disease called soil rot in sweetpotato. When the sweetpotato is invaded by this fungus, the underground portion blackens and starts to decay, round black specks appear on the tuberous root, and the plant decomposes. Thus, this disease is known for causing severe damage and yield reduction in sweetpotato. Unfortunately, most domestic cultivars are susceptible to this disease. Thus, the breeding of disease-resistant cultivars is desired. However, genetic linkage analysis in sweetpotato has been challenging because this crop has complex genomic architecture derived from highly heterozygous, hexaploids (2n =6x =90) and outcrossing nature. In recent study, genetic linkage maps were constructed using molecular markers based on retrotransposon insertion polymorphisms (Monden et al. 2015). However, due to insufficient number of mapped markers in these maps, much efforts are needed for constructing higher-density linkage maps. In this study, we constructed higher-density linkage maps using several types of molecular markers such as single nucleotide polymorphism (SNP) and retrotransposon-based for identifying gene(s) or chromosomal regions associated with the soil rot resistance.