Diversity Analysis of Sweet Potato Genetic Resources Using Morphological and Qualitative Traits and Molecular Markers

Abstract

The European Union (EU) market for sweet potatoes has increased by 100% over the last five years, and sweet potato cultivation in southern European countries is a new opportunity for the EU to exploit and introduce new genotypes. In view of this demand, the origins of the principal Italian sweet potato clones, compared with a core collection of genotypes from Central and Southern America, were investigated for the first time. This was accomplished by combining a genetic analysis, exploiting 14 hypervariable microsatellite markers, with morphological and chemical measurements based on 16 parameters. From the molecular analyses, Italian accessions were determined to be genetically very similar to the South American germplasm, but they were sub-clustered into two groups. This finding was subsequently confirmed by the morphological and chemical measurements. Moreover, the analysis of the genetic structure of the population suggested that one of the two groups of Italian genotypes may have descended from one of the South American accessions, as predicted on the basis of the shared morphological characteristics and molecular fingerprints. Overall, the combination of two different characterization methods, genetic markers and agronomic traits, was effective in differentiating or clustering the sweet potato genotypes, in agreement with their geographical origin or phenotypic descriptors. This information could be exploited by both breeders and farmers to detect and protect commercial varieties, and hence for traceability purposes.

Keywords: Ipomoea batatas; SSR markers; genetic diversity; qualitative traits.

Figure 1

Principal coordinate analysis (PCoA) of the sweet potato core collection based on molecular markers: two-dimensional centroids derived from the genetic similarity estimates computed among accessions in all possible pairwise comparisons using the whole SSR marker data set. The first two coordinates were able to explain 54% of the total variation, accounting for 31% and 23% of the total, respectively. Four different colors have been used to distinguish the accessions based on their geographical origin: blue = Brazil, red = Honduras, green = Italy, and brown = USA.

Figure 2

Genetic structure analysis of the sweet potato core collection: (A) The unweighted pair group method with arithmetic average means (UPGMA) tree of the genetic similarity estimates computed among pairwise comparisons of sweet potato accessions using the whole simple sequence repeat (SSR) marker data set, with nodes of the main subgroups supported by bootstrap values. The color scheme for this figure is the same as that used in Figure 1 (Blue = Brazil, red = Honduras, green = Italy, and brown = USA). (B) Population genetic structure of a core collection of N = 22 sweet potato accessions estimated using 11 microsatellite markers. Each sample is represented by a vertical bar partitioned into K = 3 colored segments representing the estimated membership. The proportion of ancestry (%) is reported on the ordinate axis, and the identification number of each accession is indicated below each histogram. (C) The unweighted pair group method with arithmetic average means (UPGMA)-constrained tree was built by applying the Euclidean similarity index and using the morpho-qualitative measurements of a subset of the I. batatas core collection. The positions of the samples throughout the dendrogram were kept fixed according to those ones resulting from the dendrogram in Figure 2A, and the bootstrap values supporting each node of the main subgroups were calculated.

Figure 3

Principal components analysis (PCA) of the sweet potato core collection based on qualitative traits: (A) Score plot of the first two principal components (PC1 and PC2) for the 22 sweet potatoes. (B) Eigenvectors of the variables measured for the first two principal components. Loadings (eigenvalues) for the first and second principal components were equal to 25% and 17%, respectively. TP: total phenols; TAA: total antioxidant activity; dw: dry weight.