Plant breeding has taken a "be prepared" stance in developing a new Canadian Prairie Spring (CPS) wheat variety that carries a new gene for disease resistance even before it's needed, says an Agriculture and Agri-Food Canada (AAFC) researcher in Swift Current.

The as yet unnamed HY476, which was recommended for registration earlier this year, carries the gene BT8, a new source of genetic resistance to common bunt. Resistance to common bunt in current wheat varieties is based on a single gene, BT10, which is still effective in Western Canada, but is expected to wear down over the next several years, says Dr. Ron Knox, a biotechnologist at the Semiarid Prairie Agricultural Research Centre (SPARC) in Swift Current, Saskatchewan.

"We know it is just a matter of time before we see a mutation in the disease pathogen and the old resistance no longer does the job," he says. "It's important in the breeding process, if possible, to have more than one line of resistance waiting in the wings." The AAFC Swift Current wheat breeding program is funded in part by the Wheat Check-off Fund administered by Western Grains Research Foundation.

Prairie plant breeders have done such a good job over the past 25 years in developing spring wheat varieties with common bunt resistance that the disease is rarely an issue for producers, says Knox. Because the variety registration system has, for years, placed emphasis on bunt resistance, the disease has been suppressed to the point "where it is almost undetectable," he says. "But, it is still out there and we need to maintain resistance to prevent it from becoming a problem."

Common bunt, caused by fungi, can attack spring and winter wheat crops. Prior to the development of chemical treatments and genetic resistance, it was regarded as one of the most devastating diseases of wheat in Canada and other countries.

Because the disease favours cool, moist growing conditions, it is more often found in Prairie winter wheat crops, says Knox. The disease infects the seed head, replacing the seed with a mass of brownish spores, and it affects both yield and quality. These spore clumps or bunt balls also produce an odour. Heavily infected fields and samples have often been described as having a fishy odour, says Knox.

While seed treatments are available to control bunt, plant breeders have recognized the long-term value of developing resistant varieties. AAFC breeders Dr. Ron DePauw and Dr. Julian Thomas began work in the mid '80s to backcross resistant genes into CPS and hard red spring lines. Their efforts over the years eventually led to the development of wheat varieties such as AC Carma and AC Foremost, which carry the BT10 resistance, and now HY476, which carries the new gene resistance.

"Incorporating resistance is a slow process," says Knox. "We have to put new lines out in the field, inoculate seeds with the disease and then check the progeny to see if the disease shows up. It's a matter of crossing and re-crossing lines to get material that not only has good quality and agronomics, but also carries the resistance."

The genetic resistance for common bunt was actually discovered by wheat geneticists in the Pacific Northwest Region of the U.S. more than 30 years ago. The BT10 and BT8 genes, for example, have been the prime sources of bunt resistance in wheat crops across Idaho, Washington and Oregon. However, because the cooler, wetter growing conditions in those states are prime for disease development, the turnover of bunt resistance is much faster. Breeders there need to develop varieties with new lines of resistance to stay ahead of the disease.

The disease cycle in Western Canada is much slower because of warmer, drier growing conditions, and common bunt is a good example, says Knox. While BT10 is no longer effective for U.S. growers, it has controlled the disease on the Canadian Prairies for the past 10 years and continues to do so.

Knox is also working with other common bunt resistance genes such as BT12 and BT11 for future wheat varieties. Researchers also plan to investigate the potential of pyramiding or stacking genes such as BT8 and BT10 in a single variety, which would extend the life of both genes.

The Wheat and Barley Check-off Funds, administered by the Western Grains Research Foundation (WGRF), allocate more than $4 million annually to wheat and barley breeding programs