Abstract
The genus Fragaria encompasses species at ploidy levels ranging from diploid to decaploid. The cultivated strawberry, Fragaria×ananassa, and its two immediate progenitors, F. chiloensis and F. virginiana, are octoploids. To elucidate the ancestries of these octoploid species, we performed a phylogenetic analysis using intron-containing sequences of the nuclear ADH-1 gene from 39 germplasm accessions representing nineteen Fragaria species and one outgroup species, Dasiphora fruticosa. All trees from Maximum Parsimony and Maximum Likelihood analyses showed two major clades, Clade A and Clade B. Each of the sampled octoploids contributed alleles to both major clades. All octoploid-derived alleles in Clade A clustered with alleles of diploid F. vesca, with the exception of one octoploid allele that clustered with the alleles of diploid F. mandshurica. All octoploid-derived alleles in clade B clustered with the alleles of only one diploid species, F. iinumae. When gaps encoded as binary characters were included in the Maximum Parsimony analysis, tree resolution was improved with the addition of six nodes, and the bootstrap support was generally higher, rising above the 50% threshold for an additional nine branches. These results, coupled with the congruence of the sequence data and the coded gap data, validate and encourage the employment of sequence sets containing gaps for phylogenetic analysis. Our phylogenetic conclusions, based upon sequence data from the ADH-1 gene located on F. vesca linkage group II, complement and generally agree with those obtained from analyses of protein-encoding genes GBSSI-2 and DHAR located on F. vesca linkage groups V and VII, respectively, but differ from a previous study that utilized rDNA sequences and did not detect the ancestral role of F. iinumae.
Highlights
The genus Fragaria belongs to the economically important Rosaceae family, subfamily Rosoideae
Fragaria germplasm accessions were obtained from four sources: USDA National Clonal Germplasm Repository (NCGR), Corvallis, Oregon [accessions with CFRA prefixes and USDA Plant Introduction (PI) numbers]; the collection of Gunter Staudt in Merzhausen, Germany; our own collection (GS2C, PAWT, and U2A), and W
The sequenced region of the Fragaria alcohol dehydrogenase 1 (ADH-1) gene proved to be a rich source of informative nucleotide substitutions and indel polymorphisms
Summary
The genus Fragaria (strawberry) belongs to the economically important Rosaceae family, subfamily Rosoideae. Current understanding of the cultivated strawberry’s complex octoploid (2n = 8x = 56) genome composition and reticulate evolutionary history is limited, and relies on just a few molecular studies [2,3,4,5,6]. The octoploid, cultivated strawberry, Fragaria6ananassa originated in Europe in the mid-1700s from hybridization between the ancestral octoploids Fragaria chiloensis and Fragaria virginiana [7]. These octoploids are native to South and North America, respectively, but had been brought to Europe and were being grown in proximity in European horticultural gardens [8], where hybridization ensued. The immediate and very recent ancestry of the cultivated strawberry is evident as a matter of historical record, and to further trace its ancestry is to explore the origin(s) of its octoploid progenitors
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