Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2000
Publication Date: 11/14/2000
Citation: Wang, Z.N., Hang, A., Hansen, J., Burton, C.S., Mallory-Smith, C.A., Zemetra, R.S. 2000. Visualization of a-and b-genome chromosomes in wheat (triticumaestivum l.) x jointed goatgrass (aegilops cylindrica host) backcross progenies. Genome. Interpretive Summary: Jointed goatgrasss is a devastating weed in winter wheat fields of the western United States, infesting 3 million hectares. It is closely related to wheat and can be crossed to each other. The development of herbicide-resistant wheat may provide a means to control jointed goatgrass effectively. However, this is risky if the herbicide- resistant gene could escape from wheat to jointed goatgrass through the continuous crossing and backcrossing between these two species. Cytogenetically, jointed goatgrass is a tetraploid with chromosome number 2n = 4x = 28 and consists of CCDD genomes, sharing a common D genome with wheat which is a hexaploid, with chromosome number 2n = 6x = 42, and having AABBDD genomes. If a herbicide-resistant gene is on the D genome of wheat, it could move to jointed goatgrass by homologous chromosome pairing and gene recombination. If the gene is located on the A or B genomes, it could move to jointed goatgrass by translocation or breaking and rejoining events. Therefore, a technique to identify A or B genome chromosomes or chromosome segments in a jointed goatgrass background would greatly facilitate estimation of the risk of releasing herbicide-resistant wheat. This research describes a procedure for identifying the genome A or B chromosomes and chromosome fragments in fertile wheat x jointed goatgrass backcross progenies and to assess the biological risk of releasing herbicide-resistant wheat.
Technical Abstract: Wheat (Triticum aestivum) and jointed goatgrass (Aegilops cylindrica) can cross with each other, and their self-fertile backcross progenies frequently have extra chromosomes and chromosome segments, presumably retained from wheat, raising the possibility that a herbicide resistance gene might transfer from wheat to jointed goatgrass. Genomic in situ hybridization (GISH) was used to clarify the origin of these extra chromosomes. By using T. durum DNA (AABB genome) as a probe and jointed goatgrass DNA (CCDD genome) as blocking DNA, one, two, and three A- or B-genome chromosomes were identified in three BC2S2 individuals where 2n = 29, 30, and 31 chromosomes, respectively. A translocation between wheat and jointed goatgrass chromosomes was also detected in an individual with 30 chromosomes. In pollen mother cells with meiotic configuration of 14 II + 2 I, the two univalents were identified as being retained from the A or B genome of wheat. By using Ae. markgrafii DNA (CC genome) as a probe and wheat DNA (AABBDD genome) as blocking DNA, 14 C-genome chromosomes were visualized in all BC2S2 individuals. The GISH procedure provides a powerful tool to detect the A or B-genome chromatin in a jointed goatgrass background, making it possible to assess the risk of transfer of herbicide resistance genes located on the A or B genomes of wheat to jointed goatgrass.