Submitted to: Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 5, 2012
Publication Date: April 5, 2013
Citation: Ulloa, M., Abdurakhmonov, I.Y., Perez-M, C., Percy, R.G., Stewart, J. 2013. Genetic diversity and population structure of cottons (Gossypium spp.) of the New World assessed by SSR markers. Botany. 91:251-259. Interpretive Summary: Genetic diversity is desirable for long-term cotton improvement of yield and fiber quality, and in the reduction of crop vulnerability to diseases. Genetic diversity is defined as the genetic makeup among individuals. Many species of wild cottons of the North and South American Continents also known as the New World remain unexploited, and some of them possess favorable traits lacking in modern cottons. To assess the genetic diversity and population structure in cotton species, 111 cotton accessions representing Asiatic and New World wild species were assessed using molecular markers with wide genome coverage. Molecular markers (small pieces of DNA that can be detected chemically) represent a tool that is used to study genetic diversity and genetic relationships. Marker-data from 124 molecular markers grouped all species into distinct groups, which were consistent with origin, evolutionary history, and geographic distribution or ecotypes of these wild cotton accessions, suggesting existence of clear population structures. In addition, molecular marker data was consistent with the fundamental knowledge of modern cotton formation and the rapid radiation of the American cotton linage that took place somewhere in the southwestern Mexico, following by a differentiation-speciation during plant evolution. Additional studies are needed to establish a defensible taxonomic treatment of new taxa with molecular distant and different geographical cotton types. These results improve our understanding of genetic relationships among these wild cottons and provide useful information for constructing a collection of this genetic resource for use in cotton improvement.
Technical Abstract: A global analysis of cotton (Gossypium spp.) genetic diversity is the first step to understand its geographical distribution, dissemination, genetic relatedness, and population structure. To assess the genetic diversity and population structure in Gossypium species, 111 cotton accessions representing five allotetraploids (AD1 – AD5 genomes), 23 Asiatic diploids (A1 and A2 genomes), and 82 diploids of the New World subgenus Houzingenia (D1 – D11 genomes) species were assessed using SSR markers with wide genome coverage. The average genetic distances (GD) between the two most important New World tetraploid cottons [Upland (G. hirsutum L.) and Pima (G. barbadense L.)] was 0.39. Among the three shrubs type Sections (Houzingenia, Integrifolia, and Caducibracteolata) and three arborescents Sections (Erioxylum, Selera, and Austroamericana), the GD ranged 0.19 – 0.41. Phylogenetic analyses grouped all species into distinct phylogenetic clades, which was consistent with genomic origin, evolutionary history, and geographic distribution or ecotypes of these accessions, suggesting existence of clear structured strata. Considering all genomes, the highest statistical analysis of structure test through measurements of ad hoc ('K) occurred at K = 2, with group Q1 with Asiatic diploid A genomes and with group Q2 with all the New World diploids of the D-genome. AD genome accessions shared nearly equal alleles from both Q1 and Q2 groups. Considering all the diploids of the New World D-genomes, the highest value of 'K occurred at K = 5. These results are consistent with the fundamental knowledge of tetraploid AD-genome formation and the rapid radiation of the American diploid cotton linage that took place somewhere in the southwestern Mexico, following by a differentiation-speciation during angiosperm evolution. Additional studies are needed to establish a defensible taxonomic treatment of new taxa with molecular distant and different geographical ecotypes.