COTTON GERMPLASM: RESOURCES AND TOOLS FOR CHARACTERIZATION

Authors: Percival Jr, Albert; Kohel, Russell; Yu, John

Submitted to: International Cotton Genome Initiative Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 6/6/2002
Publication Date: 6/6/2002
Citation: Percival,Jr., A.E., Kohel, R.J., Yu, J. 2002. Cotton germplasm: Resources and tools for characterization [abstract]. International Cotton Genome Initiative Workshop. p. 82.

Interpretive Summary:

Technical Abstract: Future improvement of cotton has met new challenges that require integrated tools to characterize existing genetic resources. Fragmentary data and information on germplasm characterization need to be coordinated into an integrated whole. The four domesticated species (G. hirsutum, G. barbadense, G. arboreum, and G. herbaceum) of the genus Gossypium embody considerable genetic diversity. However, this is dwarfed by the genus whose 49 species have a geographic range that covers most tropical and subtropical regions of the world. The cotton gene pool is subdivided into three sub-pools. The primary pool is limited to the tetraploid species where no genetic barriers are known to exist in any intraspecific hybrids. The secondary pool includes germplasm resources that require manipulation beyond simple crossing to obtain fertile hybrids. The tertiary pool involves species that may or may not hybridize easily with commercial tetraploids and makes trait transfer difficult. There is no reason to believe that this range in diversity does not correspond in physiological and chemical diversity. The domesticated and wild species of cotton, consequently, represent a wide genetic storehouse for potential exploitation by cotton breeders of the world. The U.S. Gossypium Collection currently maintains over 8,500 seed accessions of Gossypium species. The individual seed samples, represented in the collection, were obtained by collectors during planned plant explorations to various parts of the globe, by individuals who independently obtained seeds, and by seed exchanges or donations with other similar collections or "seed banks¿. The rationale behind the US Gossypium Collection is to preserve the broadest possible genetic base for cotton and make this available to all legitimate users. Diversity is viewed from the perspective of germplasm utilization in terms of traits that can be utilized for the improvement of the cultivated species. In this sense, more emphasis is placed on genes related to environmental fitness and physiological processes than on the morphological features important in taxonomic classification. The curatorial activities of the collection are focused on acquisition, maintenance, and distribution in order to preserve the broadest possible natural variability of Gossypium as a resource for continued efforts to modify and improve cotton cultivars. Current commercial cultivars grown today around the world have a very narrow genetic base. It is for this reason that it is imperative that we take advantage of the available gene pools. As DNA markers/clones, genetic/physical maps, and other genomic tools are being developed from cotton, they needed to characterize the US Gossypium Collection to identify redundancy and duplication from other collections and to provide guidance for evaluation and selection. A subset of the collection that represents the range of diversity of G. hirsutum and outliers of other species was subjected to molecular characterization. Pilot experiments included cottons that were genotyped with polymorphic DNA markers. DNA profiles of these cottons were analyzed and results showed strengths and deficiencies of the DNA markers. A set of 104 core reference markers is needed to serve as the standard descriptors to characterize workable sets of Gossypium accessions. Every cotton chromosome or linkage group will be covered by at least 4 markers of the core set. Although more molecular markers are needed for detailed characterization, all evaluations of cotton germplasm across different genepools and germplasm sources can be shared and pooled into a common database for gene mining analysis with the core reference markers.