Fertility and chromosome composition of wheat x jointed goatgrass backcross progeny

The first study was designed to quantify the rate of backcrossing of wheat × jointed goatgrass first generation backcross progeny (BC 1) in the field, as a rate of backcrossing of BC1 plants to jointed goatgrass alone has not been determined under field conditions. The second study sought to develop and utilize a genomic in situ hybridization (GISH) procedure to identify A- and B-genome chromosomes separately from C- and D-genome chromosomes in the wheat × jointed goatgrass second generation backcross progenies (BC2) that were generated from the work done in chapter one. These two chapters work together in assessing the biological risk of releasing wheat varieties with novel genes. The first chapter examined the rate of backcrossing of BC1 progeny to jointed goatgrass as this is the breeding direction required for introgression of novel crop genes into a weedy species. Field trials were conducted in Colorado during the 2010–11 and 2011–12 growing seasons and were supplemented with greenhouse trials to determine female fertility and self-fertility of wheat × jointed goatgrass BC1 plants. Backcrossing rates in the field were determined with germination evaluations of spikes collected from 14 BC1 plants from 2011 and 6 BC1 plants from 2012 pollinated by jointed goatgrass. Pollination by jointed goatgrass led to the production of 43 BC2 plants in 2010–11 and 1 BC2 plant in 2011–12. Mean backcrossing rates were estimated at 0.648% in 2010–11 and 0.024% in 2011–12. Median backcrossing rates were estimated at 0.041% in 2010–11 and 0.0% in 2011–12. Female fertility rates of BC1 plants were evaluated on emasculated and hand pollinated spikes from 66 plants, and resulted in a mean observed female fertility rate of 0.03%. With each successive backcross to jointed goatgrass there is a greater number of C- and D-genome bivalent chromosome pairings during meiosis, resulting in increased fertility of BC1 plants compared to wheat × jointed goatgrass hybrid plants. Because of the increase of potential bivalent chromosome pairings, male fertility has been observed in BC1 plants. With increased female and male fertility observed in BC1 plants, the potential exists for BC1 plants to self-pollinate. Self-fertility of BC1 plants was estimated on spikes from 17 plants using a single bagged spike (to prevent cross-pollination) in addition to 37 plants used in a whole bagged plant method with mean observed self-fertility of rates of 0.0% and 0.004%, respectively. These results demonstrate the first direct account of a mean backcrossing rate of BC1 plants pollinated by jointed goatgrass under field conditions. With partial self-fertility restored in the BC2 generation and shown to increase in subsequent selfing generations, BC2 individuals could propagate by seed via self-pollination even if there is no jointed goatgrass in the vicinity for pollination. Isolated patches of BC2 individuals would mark the beginning of a genetically unique jointed goatgrass population with the acquisition of novel genes from wheat and stable introgression occurring in the BC2S2 generation. Thus, the ability of BC1 plants to backcross to jointed goatgrass in the field would make it highly likely that a wheat gene conferring a selective advantage could introgress into a jointed goatgrass population. It is possible that transgenic wheat cultivars will be released in the future and determining the best management practices of these transgenic cultivars is necessary to minimize novel gene introgressions from wheat into weedy species.;The second chapter sought to develop and utilize a GISH procedure for identifying chromosomes by genome in wheat × jointed goatgrass backcross progenies. GISH has become a widely applicable cytogenetic technique for examining genome structure in interspecific hybrids and polyploid species. Direct labeling of genomic DNA from the diploid species T. urartu and Ae. speltoides was used to produce fluorescently labeled probes to visually identify chromosomes and chromosome segments belonging to the A and B genomes, respectively. Whole genomic probes showed extensive cross hybridization across all genomes when hybridized individually or hybridized with multiple probes. This resulted in fluorescent hybridization signals that were nearly homogeneously distributed among all chromosomes leading to an inability to karyotype chromosomes by genome. Varying concentrations of unlabeled genomic DNAs were unsuccessful in limiting cross-hybridization of repetitive DNA sequences to non-targeted chromosome regions. Multi-color GISH proved to be an unreliable technique for differentiating multiple genomes simultaneously in wheat × jointed goatgrass backcross progeny.;Here we have considered the rate at which wheat × jointed goatgrass BC1 plants backcross to jointed goatgrass for a second generation in the field and their genetic makeup. (Abstract shortened by UMI.).