Fingerprinting of the Global in trust Sweetpotato Collections

The International Potato Center (CIP) maintains the global sweetpotato collection in trust for humanity under the International Treaty for Plant Genetic Resources for Food and Agriculture (ITPGRFA). As part of the routine maintenance of the >5,250 accessions in the in vitro cultivated sweetpotato (Ipomoea batatas) collection, CIP has fingerprinted the entire collection to confirm the identity of the material that has been maintained in vitro for 25 years or more and also to use the fingerprint data as a long-term quality management tool. Initial fingerprints were obtained using 20 simple sequence repeat (SSR) markers. This SSR set yielded ~200 scorable alleles across the cultivated sweetpotato collection and although the SSR markers provided good discrimination of the diversity within the collection, a repeatable, high-throughput, sequenced-based marker system was desired. Due to the lack of a reference genome for sweetpotato, the options were limited for a sequence-based marker system yet preliminary results with DArTseq provided favorable results. To date, over 3,000 unique accessions have been fingerprinted by DArTseq yielding ~50,000 scorable SNPs per genotype. Reproducibility within and between runs is high, as is discrimination between accessions. Dendograms of the accessions show clear delineation of the accessions based on country of origin with sweetpotato accessions originating from Peru and Ecuador forming one large clade which is clearly distinct from clades derived of accessions from Brazil, Paraguay, Argentina, and central America. Accessions of African origin are closely related to the material from Eastern South America as has been previously suggested. This work lays the foundation for future work to compare other ex situ sweetpotato collections from around the world to determine how many unique accessions exist, the extent of the diversity in the worldwide ex situ sweetpotato collections, and to compare the ex situ diversity with that still in the field (in situ) to aid in targeted future collection missions to ensure diversity is conserved long-term in genebanks.