The plant genetics group (Blake, Lavin, McCoy and Talbert) uses a wide range of technologies and model plant systems to test hypotheses concerning the quantification and utilization of diversity in cultivated and native germplasm pools. Alfalfa (Medicago sativa L.) is an outcrossing autotetraploid (2n=4x=32), barley Hordeum vulgare L.) a self-pollinated diploid (2n=2x=14) and wheat (Triticum aestivum L.) a primarily self-pollinated allohexaploid (2n=6x=42). These cultivated species and their wild relatives span a broad range of mating systems, genome sizes and cytogenetic structures. Each group contains a large, well-documented germplasm pool which has been subjected to enormous selection pressure. The tropical legumes studied by Lavin varyin ploidy level, life cycle and mating structure. Some species in this group have been subjected to artificial selection. One goal of this group proposal is to contrast levels and types of variation in undisturbed populations with variability available in germplasm pools subjected to human intervention.
Although early agriculturists made great strides in developing modern crops, several lines of evidence suggest that the germplasm resources utilized were often extremely limited (e.g., Osborn et al., 1986; Weedin, 1992). In this regard, progress in cultivated plant improvement is constrained because of undue dependence on the progeny of plants selected thousands of years ago. Future improvement of cultivated plants will depend on what we can discover about the genetic variation in accessible germplasm pools, and to what extent such variation can be incorporated into the genomes of cultivated species. For example, the grass tribe Triticeae (of which barley and wheat are members) shows an overall similarity in terms of genome size, chromosome number and gene arrangement among species; however, most interspecific crosses yield infertile progeny. It is critical to identify which wild lineages of Triticeae contributed which genomes to the cultivated species, and then to determine whether species of the wild lineages can successfully cross with modern cultivars. Currently the laboratories of Talbert and Blake are developing molecular markers (RFLPs detected by both PCR and traditional Southern blot analysis) which will permit the comparison of DNA sequences from cultivated and wild species spanning the Triticeae. Knowing the level of genetic divergence between species of the Triticeae family at the molecular level will provide insight into the origin of genetic breeding barriers during speciation events. Similar goals are being addressed within the Medicago genus. Such knowledge may provide a means by which certain plant breeding barriers can be circumvented.
An additional goal of this project is to develop an understanding of structural genomic aspects which promote reproductive isolation in plants. Barley, wheat and alfalfa have well-characterized genomes, represent a range of cytogenetic structures, and include both self- and cross-pollinated species. We propose to estimate genetic diversity within both cultivated and wild species, and to determine the genetic distance between species related to either the crop or the wild species. We will then be able to ascertain how closely the natural process of isolation mimics the process of isolation performed through domestication.