NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
October 14, 1999
Fusarium head blight (scab) is a devastating fungal disease of wheat, but a long-term solution to this region's scab problem may be getting nearer. A research team with the USDA-Agricultural Research Service in Fargo has found that two wild relatives of wheat are excellent sources of resistance to scab.
What's more, the USDA-ARS researchers have successfully produced fertile hybrids that carry the full complement of durum chromosomes as well as a few chromosomes or chromosome segments from a wild relative that confer scab resistance.
"We have hybrids that are very promising," says Prem Jauhar, a research geneticist at Fargo's Northern Crop Science Laboratory who leads the USDA-ARS team. "We are at a very important juncture in the whole process, but we are not done yet."
The USDA-ARS team has crossed the durum cultivars Lloyd and Langdon with two remotely related wheatgrass species: Thinopyrum junceiforme and Lophoyrum elongatum. Genes from Th. junceiforme and L. elongatum have conferred scab resistance to their respective durum hybrids, says Jauhar, who explains that genes are pieces of DNA, the material located primarily in cell nuclei that determines heredity. Chromosomes are made up primarily of DNA and protein.
The incorporation of scab resistance into fertile durum hybrids represents significant progress toward developing scab-resistant durum cultivars. Jauhar's objective is to produce hybrid derivatives, or genetic stocks, that will facilitate breeding scab resistance into durum cultivars. Jauhar says his research team will continue using the tools of cytogenetics and conventional plant breeding to ensure that the wheatgrass material they've introduced into the hybrids continues to be transferred to subsequent generations. Once they've determined that the chromosome material from the wild parent is indeed stably integrated into the durum chromosome material, and that the reconstituted durum material has remained fertile, they will release it to the durum breeders, but Jauhar can provide no time line. He says the material will be crossable with both durum and hard red spring wheat breeding lines.
In 1994, Jauhar began work with FISH (Fluorescent In Situ Hybridization), a sophisticated molecular technique that allows researchers to identify alien chromosomes or chromosome segments they've introduced into a crop cultivar. Under the microscope, a specially designed probe causes the incorporated chromosomes to fluoresce, or light up. The USDA-ARS team is using FISH in their work with the scab-resistant hybrids.
While Jauhar's work is promising, commercial cultivars derived from his team's effort will appear on a longer-term horizon, says Elias Elias, the durum breeder at North Dakota State University. Even though the USDA-ARS hybrids contain all chromosomes from Lloyd and Langdon, the distantly related wheatgrass chromosomes or chromosome segments these hybrids also carry will require plant-breeding efforts to refine agronomic and quality traits.
Jauhar says wheat evolved in nature from three wild grasses: Triticum urartu, Aegilops speltoides, and Triticum tauschii. Durum resulted when T. urartu and Ae. speltoides crossed in nature, about 10,000 years ago. Durum carries the designation "tetraploid"--meaning that each of its cells contains four sets of seven-chromosome pairs, for a total of 28 chromosomes. Of the wheatgrasses the USDA-ARS team crossed with Lloyd and Langdon, Th. junceiforme is a tetraploid while L. elongatum is a diploid--carrying only two seven-chromosome pairs.
The original parents of wheat (T. urartu, Ae. speltoides and T. tauschii) were all diploids. Bread wheat is the result of the natural crossing of tetraploid wheat with T. tauschii, so bread wheat (including hard red spring) is a "hexaploid," carrying 42 chromosomes--six seven-chromosome pairs. Jauhar says geneticists prefer working with diploids, which have fewer chromosomes and thereby make the search for specific genes easier. However, if the traits researchers seek are not contained in diploids, their search must expand to tetraploids and beyond.
In 1994, Jauhar initiated research work on biotechnology at his USDA-ARS lab in Fargo. He acquired a gene gun and developed other facilities for directly transferring genes from other organisms into plants. Using these facilities, his research team produced the world's first transgenic durum wheat and standardized the techniques of direct gene transfer into durum cells. Several scientists with the USDA-ARS in Fargo and with NDSU are now using this facility. Transgenic technology, such as that available through Jauhar's lab, will help researchers incorporate anti-fungal genes of alien origin into durum wheat and thereby accelerate breeding for scab resistance.
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Source: Prem Jauhar (701) 239-1309
Editor: Dean Hulse (701) 231-6136