Submitted to: Journal of Molecular Phylogeny and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2003
Publication Date: 2/2/2004
Citation: Rajapakse, S., Nilmalgoda, S., Molnar, M., Ballard, R.E., Austin, D.F., Bohac, J. 2004. Phylogenetic relationships of sweetpotato and other Ipomoea species in series Batatas (Convolvulaceae) based on nuclear B-amylase gene sequences. Journal of Molecular Phylogeny and Evolution. 30:623-632.
Interpretive Summary: The cultivated sweetpotato is an important food crop, ranking seventh in global food production. Sweetpotato is a member of the morning glory family. There are 12 wild species and a hybrid in this family that have been classified as the closest relatives of sweetpotato based on flower form. However the high level of variability found in these traits has confounded the exact classification of these species and their relative closeness to sweetpotato. DNA technology was applied to clarify these relationships. These experiments showed that one species had been incorrectly classified and two are in a distinct subclass. A clearer understanding of these relationships is useful in devising an approach to transferring novel genes from the wild species to the cultivated sweetpotato. This would enhance the potential to transfer useful genetic traits from the wild species to the cultivated sweetpotato, such as resistance to specific pests and tolerance to cold or flooding.
Technical Abstract: Phylogenetic relationships of 13 accessions and a cultivar representing sweetpotato and wild Ipomoea species in the series Batatas were investigated using the nucleotide sequence variation of the nuclear-encoded b-amylase gene. A 1.1-1.3 kb fragment of the gene spanning two exons separated by a long intron was PCR-amplified, cloned, and sequenced. Exon sequences were highly conserved, while the intron yielded large differences. Intron analysis grouped species currently recognized as having A and B genome types into separate clades. This grouping supported the present genome designation of most species, with the exception of I. tiliacea, previously believed to be a B genome species. Evidence collected by the present study indicates that I tiliacea should be placed in the clade consisting of A genome species. From the intron alignment, sequences specific to both A and B genome species have been identified. Exon sequences indicates that I. ramosissima and I. umbraticola are quite different from other A genome species. Placement of I. littoralis is questionable; its introns are similar to other B genome species, but its exons are quite different. Exon evolution indicates that the B genome species evolved faster than A genome species. Both intron and exon results indicate I. trifida, I. tabascana and sweetpotato are very closely related to each other.