|Mcd. stewart, James|
Submitted to: Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/15/2011
Publication Date: 9/15/2011
Citation: Feng, C., Ulloa, M., Perez-M, C., Mcd. Stewart, J. 2011. Distribution and molecular diversity of arborescent Gossypium species. Botany. 89:615-624. Interpretive Summary: Variation in genetic makeup among individuals is known as genetic diversity. Genetic diversity is desirable for long-term cotton improvement of yield and fiber quality, and in the reduction of crop vulnerability to diseases. One remedy for narrow genetic diversity in cotton is to collect, evaluate and utilize a broader range of germplasm, with special emphasis on undomesticated or wild cottons. Many species of Mexican wild cottons remain unexploited, and some of them possess favorable traits lacking in modern cottons. Molecular markers (small pieces of DNA that can be detected chemically) represent a tool for studying genetic diversity and genetic relationships. We used molecular markers to assess the genetic diversity among a total of 33 specimens representing several types of wild cottons. Twenty-four of the specimens belonged to a single species called Gossypium aridum. Molecular marker data for most samples supported traditional classifications of cotton types. However, the results also indicated that the 24 specimens of Gossypium aridum exhibited more genetic diversity than was expected. Further study is needed to classify the specimens of Gossypium aridum, and to evaluate genetic relationships among them. 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: Mexico is a center of diversity of Gossypium. As currently circumscribed, arborescent Gossypium species (Section Erioxylum) are widely distributed in dry deciduous forests located from the central state of Sinaloa at the north of its range to the eastern state of Oaxaca in the south. However, extensive morphological variation exists among accessions from these different geographic/ecological regions. The objective of this work was to determine if the observed morphological variation is reflected at the molecular level. Molecular diversity and phylogenetic relationships were estimated with 210 RAPD and 766 AFLP fragments among 33 accessions of arborescent Gossypium including 24 of G. aridum, which is the most widely distributed of the arborescent Mexican diploid Gossypium species. Over 90% of the fragments were polymorphic; however, each accession contained only between 32-46% of the total loci. Two-thirds of the loci among the G. aridum accessions had allelic frequencies lower than 80%. The genetic distance between G. gossypioides (Subsection Selera) and species of Subsection Erioxylum ranged between 0.64 and 0.84. The genetic distance between two recognized species, G. lobatum and G. schwendimanii, within Subsection Erioxylum was 0.32. Most molecular data support the traditional classification of Gossypium species and the geographical ecotypes of the G. aridum accessions. A newly collected accession, US-72, of Subsection Erioxylum was genetically distant (range 0.42 to 0.54) from the other species of the Subsection. Molecular data support the recognition of this taxon as a new species. The molecular diversity among accessions of G. aridum was greater than that among the species of Subsection Erioxylum. The results indicate that the taxonomic classification of this Subsection deserves additional study to establish a defensible taxonomic treatment of the various taxa and to resolve genetically distant geographical ecotypes into new taxa.