Cultivated Sweetpotato Germplasm Collection

Sweetpotato is the seventh most important food crop, in terms of production, in the world. Sweetpotato is grown mainly in developing countries with 80% of the world’s production coming from Asia, about 15% in Africa, and only 5% from the rest of the world. Sweetpotatoes rank as one of the healthiest vegetables, because of high levels of Vitamins A and C, iron, potassium, and fiber and contains thiamin (B1), riboflavin (B2) and pantothenic acid. Beta carotene is the most abundant pigment (provitamin A) in orange flesh sweetpotato varieties which is important in countries where they were introduced to combat vitamin A deficiency in children (CIP scientist won the world food prize for their work with orange flesh sweetpotato). Purple fleshed sweetpotatoes are a rich source of anthocyanins, which have medicinal value as anti-oxidants and cancer preventing agents.

The International Potato Center (CIP) maintains one of the world’s largest cultivated sweetpotato genebanks with over 5000 accessions maintained in vitro. The overall objective is to conserve the diversity in the collection and make it available to the global community for research, breeding, and training.

Almost the entire cultivated collection (5909 accessions, 97%) was genotyped by high density Diversity Arrays Technologies sequencing (HD-DArTseq). The genetic identity of 90% of the in vitro conserved sweetpotato collection has been verified by morphological characterization using 27 standard descriptors for sweetpotatoes (CIP, AVRDC, IBPGR. 1991), and a set of 20 SSR primers.

Geographic distribution of Ipomoea Batatas
Geographic distribution by continent
Morphological characterization of sweetpotato

The morphological characterization is done using 30 standard descriptors for sweetpotatoes (CIP, AVRDC, IBPGR. 1991.) in the field of the San Ramón station in the department of Junín at 800 meters above sea level.

Thirty standard sweetpotato descriptors
1. Twinning
2. Plant type
3. Ground cover
4. Vine internode diameter
5. Vine internode length
6. Vine pigmentation-Predominant vine color
7. Vine pigmentation-Secondary vine color
8. Vine pubescens
9. General outline of the leaf
10. Leaf lobes type
11. Leaf lobe number
12. Shape of central leaf lobe
13. Leaf size
14. Leaf vein
15. Foliage color-Mature leaf color
16. Foliage color-Inmature leaf color
17. Petiole pigmentation
18. Petiol length
19. Storage root shape
20. Storage root surface defects
21. Thickness of cortex
22. Skin color 1 Predominant color
23. Skin color 2 Intensity of predominant color
24. Skin color 3 Secondary skin color
25. Flesh color 1 Predominant color
26. Flesh color 2 Secondary flesh color
27. Flesh color 3 Distribution of secondary flesh color
28. Storage root formation
29. Latex production in storage roots
30. Oxidation in storage roots
Molecular characterization of sweetpotato

The genetic diversity maintained in the genebank is well characterized enabling better use and targeted selection and use of material by breeders, molecular biologists, taxonomists, and other germplasm users.

Currently a highly informative and user-friendly set of 20 SSR primers, which covers most of the sweetpotato genome, has been selected and is used to fingerprint accessions, assess diversity and aid in phylogenetic studies.

These SSR fingerprints provide a molecular ID for the accessions for in house quality management as well as for scientific investigations. One example of their use in genebank management has been the confirmation of identity of the in vitro collection by comparison of SSR fingerprints with material maintained from the originally collected samples.

Molecular fingerprint of sweetpotato using SSRs. The band pattern corresponds to SSR locus IBS11.

Important subsets available for distribution

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Collaboration with La Buena Esperanza school

Combat malnutrition and childhood anemia through consumption of sweetpotato.

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Wild Relatives of Sweetpotato

Crop wild relatives represent a diverse gene pool which can contribute beneficial traits such as resistance to biotic (insects and diseases) and abiotic (drought, frost, salinity) factors to crop improvement programs. The genetic erosion and loss of habitat of these valuable crop wild relatives is occurring as human populations grow and expand and variable climate changes natural habitats too rapidly for the plants to adapt. This put pressure on us to preserve theses wild relatives in genebanks before they are permanently lost. The genebank from the International Potato Center (CIP) maintains 1,092 wild sweetpotato accessions corresponding to 67 species from 19 countries. The wild collections are conserved as populations as seed in -20°C cold chambers. This includes the Batatas Series which consists of 13 species.

Seed regeneration of wild sweetpotato is undertaken using a few fundamental principles to produce enough seed for distribution while still maintaining as much allelic diversity as possible from the original collection. During regeneration, the accession is also characterized using standard genebank descriptors. Flower formation of sweetpotato, Ipomoea batatas (L.) Lam., and its wild relatives is challenging because flowering is dependent on various environmental conditions, some of which are still active areas of research to determine what is needed for flowering and seed formation. Flowering can vary widely in different seasons/years from poor to abundant. Some accessions produce little or no flowers like those from the species I. ramossisima, I. tiliaceae, and I. tabascana. For species and accessions which produce few flowers, the induction of flowering is often successful by an assortment of methods including a shortened photoperiod, increased humidity, chemicals, grafting onto other Ipomoea species or increased nutrient fertilization.

Seed Regeneration of Wild Relatives of Sweetpotato

Seed Germination

Harvest seed

Maintenance of plant material

Sealing the seed envelopes

Pollination

Seed storage

Ploidy Determination of Sweetpotato Wild Relatives by Flow Cytometry

Flow cytometry is a technique used for the determination of ploidy and nuclear DNA content. A major advantage of flow cytometry is the large number of nuclei analyzed in a very short period of time. This allows a rapid screening of large amounts of samples from breeding experiments, in-vitro regeneration, routine analysis for identity or compatibility checking or characterization studies in a genebank. Chromosome counting is performed for results validation.

Collection of young leaves

Flow cytometry analysis

Validation

Taxonomic classification of Batata series and ploidy level(s)

Ipomoea spp. Ploidy 2n (x=15)
I. batatas 6x, 4x
I. cordatotriloba 2x, 4x
I. cynanchifolia 2x
I. x grandifolia 2x
I. lacunosa 2x
I. x leucantha 2x
I. littoralis 2x
I. ramosissima 2x
I. tabascana 4x
I. tenuissima 2x
I. tiliacea 4x
I. trifida 2x, 4x, 6x
I. triloba 2x