Winter Crop Research
Frozen by Karnal Bunt

by Tracy Sayler

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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.

North Dakota State University, South Dakota State University, and the University of Minnesota, among other public and private crop breeding programs, all have winter crop nurseries near Yuma, AZ. The arid environment is ideal in preventing many foliar pathogens from forming, that could affect seed increases from promising new wheat lines.

The Karnal bunt outbreak in Arizona and the subsequent federal quarantine, however, has meant that most seed harvested from experimental lines in the winter nurseries ("grow-outs," in plant breeder talk) near Yuma will not be brought back to NDSU, SDSU, and U of M trial plots and crop nurseries this summer.

With the quarantine, interstate movement of possible carriers of Karnal bunt spores has become highly restrictive. Karnal bunt spores can be carried on a variety of surfaces, including plants, seeds, soil, farm equipment, tools, and even vehicles. The detection of a spore doesn't mean the disease is present; a susceptible host and the right conditions are needed for spores to develop into the Karnal bunt fungus.

Wheat material may be brought back under quarantine and grown under isolated greenhouse conditions, with highly stringent handling requirements. But with hundreds and even thousands of affected lines to consider, and to prevent interruptions in the summer breeding schedule as well as to other greenhouse research projects, this is a realistic option wheat breeders have for only a few select lines.

Operation desert spores

Karnal bunt (Kb) is a fungal disease of wheat, including durum, and triticale (a hybrid of wheat and rye). Barley, oats, and rye are not susceptible to Kb, and durum is less susceptible to Kb than bread wheats.

Infected grain will yield slightly less, and quality becomes affected. Flour made from bunted kernels can become discolored and develop a fishy odor and taste. The disease poses no threat to human health, but wheat containing more than 3 percent bunted kernels is generally considered unfit for human consumption.

In the quarantine areas of the southwestern U.S., the USDA has taken extraordinary measures to ensure containment. Some wheat acreage has been destroyed, with affected growers indemnified by the U.S. Government to cover their losses. Other affected acreage has been harvested under controlled conditions for non-seed use only within the quarantine area. Wheat, as a host crop, cannot be planted in any contaminated field for a period of five years. That's about how long spores that carry Kb can survive in the soil.

This summer, the USDA will begin surveying about 2,500 country elevators in 42 states for the presence of Kb, in an extension of the federal containment effort. If infected grain is found during the voluntary sampling process, an affected grain handling facility would receive federal reimbursement for the losses.

Research most affected in the Northern Plains

Karnal bunt has never been detected in the Northern Plains. It is not known whether the Kb fungus has the ability to overwinter here. Government containment efforts should go a long way in assuring that Kb won't occur in other wheat-producing areas of the United States, and that U.S. wheat export won't be affected. For now, the only real casualty in the Northern Plains because of Karnal bunt is research progress.

"This has ripped a hole in our program. It affects progress in the whole system," says Bob Busch, USDA-ARS wheat breeder at the U of M. Busch says he'll lose a year to two years of wheat breeding progress because of the quarantine on his winter grow-outs. The severity of the setback depends on how much remnant or back-up seed from promising lines that stayed in Minnesota over the winter, and wasn't used in the Arizona nursery.

Busch is particularly frustrated because the interruption will come at the expense of a stepped-up effort over the last few years to breed varietal resistance to scab, a disease he says that's even more significant and has caused more economic losses than Karnal bunt.

"This is a serious thing politically, but biologically, Karnal bunt ranks below many others in so far as potential devastating effects. Scab has been much more devastating to us. People have literally been put out of business because of scab," says Busch.

Roger Jones, U of M extension plant pathologist, has mixed feelings about the Kb issue. Efforts by the USDA to eradicate Kb should be supported; he says steps taken now will help prevent Kb from becoming a bigger problem.

But at the same time, he wishes scab received the same amount of federal attention: scab has affected many more acres and producers across the United States, yet the problem has received a fraction of the federal resources being allocated to Karnal bunt.

Busch has been burned by Karnal bunt before: he had to abandon his former research site and breeding materials in Mexico in the early 1980s due to Kb. He lost two to three years of breeding advancements then; this latest incident isn't any easier to swallow. "The loss of Arizona for winter grow-outs would be significant. Arizona is a huge distribution area for seed increases used by a lot of people," which he says includes land-grant colleges, federal and private research, even a world germplasm bank, which includes germplasm from close to 40,000 wheat lines. Much remnant seed remains in the world germplasm bank, unaffected by the Kb quarantine.

The Kb quarantine complicates cooperative scab nursery tests which involves Canada. NDSU, SDSU, Agriculture and Agrifood Canada (the equivalence to USDA) and the U of M all exchange breeding materials to test for scab tolerance. Busch coordinates the exchange of materials for the uniform scab nursery: he says that durum lines in this case couldn't be exchanged with Canada this year, because of the tougher international phytosanitary measures. However, hard red spring wheat material was successfully exchanged for testing.

SDSU spring wheat breeder Jackie Rudd says lost time is one of the biggest consequences, "and it's hard to put a value on what that loss of time is." A single head of wheat can yield up to a pound of seed in a generational grow-out. With the lines he left behind at Yuma, "that's one-half bushel for every acre from now on I'm not going to get back."

Scott Haley, SDSU winter wheat breeder, says there is less need for a winter grow-out site for winter wheat than there is for spring wheat. But Haley used the Yuma site for the first time last winter to make some winter wheat increases, and lost about 250 crosses. "It's a hit, but I've got other crosses to rely on. And unlike the spring wheat breeders, I don't have to plant until next September, so there's a chance I could get some material back yet from Arizona." Haley says he was hoping to step up his use of the Yuma site for hard white wheat breeding, as the climate there reduces the chance for seed weathering.

Canadian crop breeders have also been affected by the Kb outbreak, as they have winter nurseries in southern California, and have been affected by the Kb quarantine. Fred Townley-Smith, wheat breeder with Agriculture and Agri-food Canada in Winnipeg, says that under normal circumstances he would have brought 7,000 to 8,000 lines of small grains back to Canada; but that material will likely stay at the California research site, indefinitely.

Townley-Smith has another nursery in New Zealand that is unaffected by the quarantine, but some parts of the breeding program will suffer generational setbacks nonetheless.

AgriPro has limited winter nurseries in New Zealand and Argentina, and conducts much of its seed breeding in greenhouses near Fort Collins, Colo. However, the company did have seed from its new variety Gunner in Yuma last winter to speed up increases to get seed to market sooner. Gunner has good scab tolerance; better than 2375 and most other spring wheat varieties currently available to growers, says Bob Knudson, AgriPro's northern wheat manager.

"We're not going to be able to bring Gunner seed back from Arizona, even though it tested negative for Karnal bunt. We had hoped to have certified Gunner seed to growers next year, but now it won't be available until 1998," says Knudson.

NDSU wheat breeder Richard Frohberg had about 1,500 experimental wheat lines left in Yuma, that he wanted to bring back to North Dakota for summer trials. He intends to recover some of the lines with no remnant seed and increase them under quarantined greenhouse conditions. Like other wheat breeders, some parts of his program have been set back as much as two years.

It appears likely that crop breeders will need to find a new winter nursery location. Possible locations are New Zealand, Chile, Hawaii, Ecuador, Puerto Rico, or somewhere in the Caribbean region. "At this point, all we know is that it's going to be more expensive," says Frohberg. There would be some advantages in moving further south, however: Longer days would enhance seed increases, and grow-outs would be accomplished sooner.

Sharing a common winter nursery site worked well in Yuma, Rudd says, and should be considered by the land-grant colleges in the Northern Plains again, even if only to share the increased expenses of what looks to be a new overseas site.

U of M brings barley back
from Arizona; NDSU does not

The University of Minnesota decided to bring seed back from experimental lines grown in its winter barley nursery near Yuma, Ariz. Otherwise, the U of M barley breeding program effort to develop cultivars with resistance to scab would have suffered a serious setback.

Detection of Karnal bunt in Arizona resulted in concern about infections in other wheat-producing areas of the United States, and subsequent federal quarantine measures. "But it's awfully important to point out that Karnal bunt doesn't attack barley. It is a non-host crop," says U of M barley breeder Don Rasmusson.

The U of M decision came only after consultation with the Minnesota Department of Agriculture, the American Malting Barley Association, and input from the Northwest Experiment Station and the Minnesota Barley Research and Promotion Council.

Also lending support to the decision: Infection occurs during the flowering stage of a host plant, and wheat fields in the area of Yuma had not flowered when the barley lines were harvested. Further, the U of M barley lines were grown in a Karnal-bunt free area, where the disease has not been detected.

Still, the U of M took special preventive precautions. The barley seed was tested and cleared by the Arizona Department of Agriculture before it left the state, and it was tested again when it arrived in Minnesota, with no traces of Karnal bunt spores found. Finally, barley from the Arizona nursery will only be planted in controlled test plots located at the Agricultural Experiment Stations at St. Paul, Morris, and Crookston.

Busch Ag Resources returned barley lines from its Arizona nursery site to Colorado, following similar precautionary measures.

NDSU officials, meanwhile, decided that no matter how remote the risks may be, it would not bring seed back from any crops grown in Arizona winter test plots, whether it be wheat or non-host crops such as barley, dry beans, or crambe.

"It will be a setback of up to two years for parts of my barley breeding program," says Rich Horsley, NDSU's six-row barley breeder. Horsley had to leave about 350 six-row lines behind in Arizona, many of which were being bred for increased resistance to problem diseases, such as rusts.

Rasmusson is optimistic about making further research progress this summer in his objective, to develop barley with more scab tolerance. He says the U of M's scab research effort on barley is young, beginning only after the severe scab year of 1993, and could not have afforded an interruption.

"The seed we got back from the Arizona grow-outs is in good shape. This summer, we hope to accumulate a lot of information on vomitoxin production in barley, among other characteristics related to scab, and to have barley lines to move to increase rapidly," Rasmusson says.

Photo Credit: USDA, APHIS

Copyright Prairie
Grains Magazine
June 1996