Characterization and development of EST-derived SSR markers in cultivated sweetpotato (Ipomoea batatas)

In this study, we investigated 181,615 ESTs for the identification and development of SSR markers. In total, 8,294 SSRs were identified from 7,163 SSR-containing unique ESTs. On an average, one SSR was found per 7.1 kb of EST sequence with tri-nucleotide motifs (42.9%) being the most abundant followed by di- (41.2%), tetra- (9.2%), penta- (3.7%) and hexa-nucleotide (3.1%) repeat types. The top five motifs included AG/CT (26.9%), AAG/CTT (13.5%), AT/TA (10.6%), CCG/CGG (5.8%) and AAT/ATT (4.5%). After removing possible duplicate of published EST-SSRs of sweetpotato, a total of non-repeat 7,958 SSR motifs were identified. Based on these SSR-containing sequences, 1,060 pairs of high-quality SSR primers were designed and used for validation of the amplification and assessment of the polymorphism between two parents of one mapping population (E Shu 3 Hao and Guang 2k-30) and eight accessions of cultivated sweetpotatoes. The results showed that 816 primer pairs could yield reproducible and strong amplification products, of which 195 (23.9%) and 342 (41.9%) primer pairs exhibited polymorphism between E Shu 3 Hao and Guang 2k-30 and among the 8 cultivated sweetpotatoes, respectively.This study gives an insight into the frequency, type and distribution of sweetpotato EST-SSRs and demonstrates successful development of EST-SSR markers in cultivated sweetpotato. These EST-SSR markers could enrich the current resource of molecular markers for the sweetpotato community and would be useful for qualitative and quantitative trait mapping, marker-assisted selection, evolution and genetic diversity studies in cultivated sweetpotato and related Ipomoea species.Sweetpotato (Ipomoea batatas) is a hexaploid (2n = 6x = 90) dicot and belongs to the family of Convolvulaceae. Due to its high yielding potential and adaptability under a wide range of environmental conditions, sweetpotato is one of the world's important food crops, especially in developing countries. According to the Food and A