Submitted to: Taxon
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/20/2004
Publication Date: N/A
Citation: Interpretive Summary: It is important for plant breeders to understand the relationships among squash species to produce improved varieties that allow the grower to become more competitive the global market place. Genetic diversity (differences among DNA which compose genes which provide the expression of the characteristics that humans can see) in squash (scientific name = Cucurbita pepo L.) forms the basis for recognition of five infraspecific groups (different types such as crookneck and zuchinni) representing three wild and two domesticated (selected by man through time) groups. The domesticated groups consist of cultivated pumpkins, marrows, and a few ornamental gourds (Group 1), and the crooknecks, scallop squashes, acorn squashes, and most ornamental gourds (Group 2). The wild groups consist of free-living populations in the Greater Mississippi Valley and the Ozark Plateau, Texas, and northeastern Mexico. These groups of squash were investigated at the DNA level of complexity (single components of genes). The data indicate that these species are very different and have likely been domesticated by man in different regions of North, Central, and South America. The have very different DNA components and an understanding of these components will allow plant breeders to increase their effectiveness in producing improved varieties of squash and to allow for the use of wild groups in crossing to commercial groups to diversify the genetic make up of squash. This increase in genetic diversity will provide for varieties that are unique to American agriculture, thus allowing the grower to be more competitive in a global market place.
Technical Abstract: Five hypervariable regions of plastid DNA were surveyed for single nucleotide polymorphisms (SNPs) that might be useful for revealing evolutionary relationships and nucleotide substitution patterns in the domesticated squash Cucurbita pepo L. Seven such SNPs were found in four of the five plastid regions. Phylogenetic analysis of these data, using C. argyrosperma subsp. sororia as outgroup, confirmed previous evidence that C. pepo subsp. ovifera and subsp. fraterna are genetically distinct lineages that share a common ancestor not shared with subsp. pepo. However, none of the SNPs distinguished among the three varieties of subsp. ovifera. Six of the seven substitutions within C. pepo were part of the G to A to C to T to G series of substitutions that had been previously documented for the Cucurbitaceae. The seventh substitution was T to A, while three of the ten SNPs occurring between C. pepo and C. argyrosperma were also A:T to T:A transversions. Taken together, the substitution data suggest that one or more mechanisms favoring the success of G:C to A:T, A:T to C:G, and A:T to T:A substitutions are operating in Cucurbita.