The Use of DNA Sequences from the β-Amylase Gene to Determine the Genetic Relationship among Sweetpotato, I. batatas and Other Ipomoea Species in Series Batatas (Convolvulaceae)

in HortScience

The sweet potato Ipomoea batatas (L.) Lam. is classified in series Batatas (Choisy) in Convolvulaceae, with 12 other species and an interspecific true hybrid. The phylogenetic relationships of a sweetpotato cultivar and 13 accessions of Ipomoeas in the series Batatas were investigated using the nucleotide sequence variation of the nuclear-encoded β-amylase gene. First, flowers were examined to identify the species, and DNA flow cytometry used to determine their ploidy. The sweetpotato accession was confirmed as a hexaploid, I. tabascana a tetraploid, and all other species were diploids. A 1.1–1.3 kb fragment of the β-amylase 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 sequence differences. Intron analysis grouped species currently recognized as A and B genome types into separate clades. This grouping supported the prior classification of all the species, with one exception. The species I. tiliacea was previously classified as a B genome species, but this DNA study classifies it as an A genome species. From the intron alignment, sequences specific to both A and B genome species were identified. Exon sequences indicated that I. ramosissima and I. umbraticola were quite different from other A genome species. Placement of I. littoralis was questionable: its introns were similar to other B genome species, but exons were quite different. Exon evolution indicated the B genome species evolved faster than A genome species. Both intron and exon results indicated the B genome species most closely related to sweetpotato (I. batatas) were I. trifida and I. tabascana.

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