Feb/March 1998
Crop Breeders Making Progress in Developing Scab Tolerant Varieties
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.
Management techniques will help minimize the scab problem in small grains, but there are two key factors needed to bring the disease under control: better weather, and better varieties. God only knows about the weather. Significant progress is being made, however, in developing scab-tolerant varieties.
Call it foresight, scientific curiosity or just plain luck, but the University of Minnesota breeding program - with funding in part by the Minnesota wheat checkoff - had already began researching sources of resistance to scab in the early 1980s. A scab nursery was initiated in 1986 at the Experiment Station in St. Paul to evaluate scab-resistant lines. Since scab was not a major problem then, the research at the time was not a major priority.
That changed, however, after the 1993 scab epidemic. The U of M put most of its traditional wheat breeding program on hold to focus virtually all efforts on breeding for scab resistance.
An increase in scab research funding now has about 20 principal investigators involved with Fusarium head blight research at the U of M, with wheat lines screened for scab resistance at three scab nurseries in Minnesota: the St. Paul Ag Experiment Station, the West Central Experiment Station in Morris, and the Northwest Experiment Station in Crookston. Different germplasm which is unadapted to Minnesota is being used, including Asian sources of resistance. Scab has been a major problem in China for decades, and resistant germplasm sources have been identified in ongoing research efforts there.
Northern crop breeders use off-season breeding locations to speed up the varietal development process. The loss of the Arizona research site due to the Karnal bunt outbreak in 1996 set research back for public and private wheat breeders by a year. The winter nurseries are now back on track, but not all at the same location; some are in California, some in New Zealand.
Since 1993 the U of M wheat breeding program has released two varieties - Verde and Bacup. Bacup was the first variety available to growers with a Chinese source of scab resistance in its pedigree. Verde has half of its parentage from the U of M, and from germplasm donated by Pioneer when the company abandoned its wheat breeding program in the early 1990s. Verde doesn't have any Chinese sources of resistance in its background, but similar to distant cousin 2375, it contains a fair level of tolerance against the spread of scab in the wheat head, what crop breeders call type II resistance; as well as some ability to maintain sound kernels despite presence of scab, or type III resistance.
Bacup exemplifies the challenge a crop breeder has in developing foreign, unadapted germplasm, and breeding desirable traits into a new variety suited for our growing area, while isolating undesirable traits. Bacup has high protein and test weight, and, under heavy to extreme disease pressure, will have an average yield. However, it is a non-performer when scab is not a problem, with poor straw strength and a yield of 10 to 15 bushels less than top performers.
The U of M will release another transition variety this year for seed increase; yet unnamed, the new variety will be generally available in 2000. It demonstrates good tolerance against the spread of scab in the wheat head, but under extreme disease situations does not posess kernel tolerance the way Bacup does. However, the new line demonstrates much better yield potential than Bacup. USDA-ARS wheat geneticist and wheat breeder Bob Busch also has another line nearing release, with good scab tolerance that yields well.
South Dakota State University spring wheat breeder Jackie Rudd has two transitional lines nearing release. After registered and certified seed production, one may be ready for general release in 2000, the other in 2001.
"They do not include Chinese sources of resistance, but similar to 2375, are field tolerant. The line that will be released first is not as high yielding as the second, but has better scab tolerance," says Rudd. "Without scab, the first line is equal to 2375 in yield; and in moderate to high scab, it should outyield 2375. The second line is considerably higher in yield compared to 2375, with scab tolerance considerably better than 2375, but still not at the level of resistance we will finally get from Oriental sources of resistance."
Rudd hopes to follow these lines with a spring wheat variety that's even more scab tolerant, from Chinese sources of scab-resistant germplasm, for seed production in 2001 and general release in 2003.
Richard Frohberg, North Dakota State University spring wheat breeder, also is making progress in breeding for scab tolerance. He is developing a transitional variety with good yield and type II scab resistance for general release by 2001, possibly sooner. This will be followed up by lines Frohberg is developing with Chinese scab-resistant germplasm that would have even stronger scab resistance and other improved characteristics such as leaf spotting resistance and better quality.
Private development efforts
Greg Fox, with Western Plant Breeders, is working on developing a new line, yet unnamed, that will be similar to 2375, with better scab tolerance than Sharpshooter. Fox says seed for the line is currently being increased in winter nurseries in Arizona. "If things go perfectly from here, release would be in the year 2000," he says.
Bob Knudson, Agripro's northern wheat seed manager, says that "Gunner is as good as there is for us, until we have something better for scab tolerance. We do have a more scab-tolerant variety under development that includes Asian material not in Gunner." That is set for release in 2000. Wheat research and development takes time as well as money - it costs $350,000 to $400,000 to develop a new variety, says Knudson.
"We're supportive of all breeding programs to solve scab. In my 40 years in the wheat business, this is one of the most challenging things I've seen. We have to save the industry. That's our goal."
More challenging for durum
Belzer was released by NDSU last year, and will be generally available in 2000. It has moderate resistance to scab and has the highest performance against scab and vomitoxin among all current durum cultivars. However, on average, Belzer has lower test weight than all medium/tall height durum varieties. Breeding of advanced lines with scab tolerance continues at NDSU.
Durum is more suceptible to scab than hard red spring wheat. Elias Elias, NDSU durum breeder, says durum spikelets are more concentrated and closer together. This may lead durum heads to stay wetter longer, increasing the susceptibility to the spread of scab. Durum also has a different genetic makeup: it has two sets of chromosomes, while spring wheat has three.
Breeding for scab resistance is more of a challenge for durum than spring wheat, since there are virtually no sources of resistance to use for crossbreeding. "There is nothing for durum like the Chinese sources of resistance such as Sumai 3 in spring wheat. We tried to transfer Sumai into durum, and it didn't work. We're trying to manipulate the genetic makeup of durum so it can be transferred, but that could take a decade. We're also looking at wild relatives of durum and finding some level of resistance, but not as much as Sumai."
Elias says he may have a new durum variety equal to Belzer in scab tolerance ready for release in the next two to three years. But a true scab resistant durum variety may still be ten years away. Finding a source of resistance or a way to transfer resistant sources of spring wheat germplasm into durum through biotechnology would speed the process, he says.
Two-row, six-row dilemma
Development of scab-tolerant barley lines is a top priority for northern crop breeding programs, and screening for deoxynivalenol (DON, or vomitoxin) is even more important in barley than in wheat. Since malting barley is used for malting and brewing, scab-induced beer gushing and vomitoxin produced by scab are key quality issues for the industry. The development of varieties with durable resistance or tolerance is the best long term solution, says Mike Davis, president of the American Malting Barley Association.
The Minnesota Agricultural Experiment Station has released a new six-row barley variety called MNbrite (MNS85 as an experimental line). It will be grown on limited acreage for seed production this year. U of M barley breeder Don Rasmusson says MNbrite is about 50% more tolerant to scab and vomitoxin than Robust. It is equal in yield, more susceptible to lodging, earlier maturing, and higher in protein compared to Robust. MNbrite has not yet been accepted by the industry for malting; its malting and brewing characteristics are being evaluated, and plant scale testing is underway.
Because this variety showed promise and there is a critical need for scab-tolerant varieties, MNbrite skipped AMBA's pilot scale evaluation program and was advanced directly to plant-scale evaluation.
Pilot-scale testing involves a malting and brewing analysis of 60 pounds of seed from the experimental line, using Morex as a check. AMBA prefers at least two years of pilot-scale testing data before an experimental line moves further to plant-scale testing, where it is grown on 700 acres to get about 30,000 to 35,000 bushels of seed for malting and brewing analysis, conducted at facilities of AMBA members.
"MNbrite is a step forward, but by no means a superior variety," says Rasmus-son. He is using MNbrite and two-row barley germplasm as progeny to develop a better malting variety that could be released by the U of M in another two to three years. "I would sure hope to have something in place for growers with acceptable quality and better scab tolerance within four to five years. We have to have the cooperation of everyone, including the industry," says Rasmusson.
"The earliest we could have a six-row in pilot-scale testing is two years, and assuming it would pass that test, it would go to plant-scale testing. Assuming it would be accepted by the industry, we could have a release by 2003 under the current system," says Rich Horsley, six-row barley breeder at NDSU. However, if an experimental line shows promise, AMBA would be expected to expedite the testing process, as it did with MNBrite, and a variety could be released sooner.
Busch Ag Resources is developing a six-row that is promising, with good quality and scab tolerance. It will go through plant-scale testing this year and might be released in 1999.
Conlon is a new two-row barley released by NDSU that is scab-tolerant. There are other two-row varieties with scab tolerance as well, including some Canadian varieties, such as AC Oxbow. But just as there are crossbreeding difficulties in transferring scab tolerance from spring wheat to durum, there are similar crossbreeding difficulties with two-row and six-row barley cultivars. So why not simply grow two-row barley for malting in the Red River Valley?
Several reasons: one is that these varieties are adapted to more arid climates, and to be accepted in the Valley, the yield potential, straw strength, and spot blotch resistance of such cultivars would need to be comparable to six-row cultivars. Also, these varieties would need to be accepted by the industry for malting. Anheuser-Busch, Miller, and Stroh are the biggest industry players in the Valley, and may be hesitant to change time-honored brew recipes that traditionally include six-row malting barley.n
(This information is sponsored in part by the Minnesota Scab Initiative)
A look at the wheat breeding process
SDSU expects to release some scab-tolerant material ahead of this schedule. North Dakota State University and the University of Minnesota plan to have more scab-tolerant lines available to the public before 2005 as well.
In the wheat breeding process, a cross is made (seed from one head of a line well-adapted to the northern area, with seed from a head of a scab-resistant line, such as the Chinese material, Sumai 3). This produces what wheat breeders call F1 seed. A row of F1 seeds are planted and harvested, and from that seed increase comes F2 seed.
The process is not absolute; it might be accelerated by more intensive, expanded techniques, or suffer unexpected setbacks - such as the Karnal bunt outbreak in 1996, which disrupted the winter nursery site in Arizona that most northern public and private wheat and barley breeders had been using. The loss of this site set scab breeding efforts back by a year.
American Cyanamid announces $25,000 matching grant to support scab research
American Cyanamid has announced a Scab Research Matching Grant to encourage grower support for ongoing research efforts aimed at bringing the scab fungus under control. The announcement was made during the National Association of Wheat Growers convention last month in San Diego.
"With nationwide scab losses since 1991 totaling more than $3 billion, we are pleased to offer this grant as it will attract vital dollars in 1998 for scab research. We hope that the support of wheat growers will help us to further scab research and preserve the future of the wheat industry," said Guy Zummo, manager of the company's well-known herbicide products, Assert and Avenge.
Through the Scab Research Matching Grant, Cyanamid will match, dollar for dollar, every "Harvest Point" award credit contributed up to $25,000. Growers earn Harvest Points award credits through the "Harvest Partners" preferred customer program with qualified purchases of American Cyanamid crop protection products, including Assert and Avenge, purchased from participating dealers. These points can then be redeemed for products and services offered exclusively through the Harvest Partners program. Contributions of Harvest Points award credits to scab research will be matched through December 31, 1998 or until the contribution equals $25,000.
The money will be donated by Cyanamid on a quarterly basis to the North Dakota Grain Growers Association and the Minnesota Association of Wheat Growers, who will be responsible for allocating the scab research funds.
Growers can simply indicate the amount to be contributed to scab research on their Redemption Request Forms which are enclosed in Harvest Partners preferred customer program statements.
For more information about the Scab Research Matching Grant or to request a Harvest Partners enrollment form, growers can call the Harvest Partners program service center at 1-800-258-2345 or visit their local Cyanamid dealer for details.
Minimizing scab at planting
No wheat varieties are totally resistant to scab, but some vari-eties have shown more tolerance. Planting at least two or three tolerant wheat varieties with differing maturity dates will help minimize the risk of scab infection. In a wet year, however, large quantities of the fungus which causes scab are produced, subjecting virtually any wheat field to some degree of scab infection. Check variety trial results to see which varieties performed the best in the presence of scab (Nov/Dec 1997 Prairie Grains Magazine).
According to North Dakota State University, varietal reaction to scab is given as one of six categories:
Very susceptible: AC Elsa, Glupro, Gus, McNeal, Majestic, Norm, Sonja, Splendor, CDC Teal, Wheaton, 2398.
Susceptible: Amidon, Bergen, AC Cadillac, Coteau, Ernest, Grandin, Hamer, Keene, Kulm, Lars, Nora, Norlander, Oxen.
Moderately susceptible: Bacup, Butte86, AC Domain, Forge, Len, Marshall, Nordic, Prospect, Russ, Sharp, Sharpshooter, Stoa, Verde.
Moderate or intermediate: AC Barrie, Gunner.
The other two categories are moderately resistant and resistant. No wheat released to date can be reliably considered resistant, although experimental lines now under extensive testing at NDSU and in other public breeding programs may soon achieve this goal.
NDSU says some varieties, although susceptible to scab to a varying degree, show less yield loss or scabby grain from scab than others, exhibiting yield or grain tolerance. These varieties include Majestic, Splendor, Coteau, Hamer, Russ, Sharp, Verde, Trenton, 2370, and 2375.
Of current durum varieties, only Rugby is categorized by NDSU as moderately susceptible. All the rest are susceptible or very susceptible, although Ben, Munich, and Renville, along with Rugby, have shown less yield loss or scabby kernels than would be expected based on the appearance of the plants in the field.
A 56-pound test weight and 85% germination should be minimum standards for saved seed. A seed quality and germination test of saved seed is recommended. The University of Minnesota Plant Disease Clinic will analyze seed for quality and germination. Contact the clinic at (612) 625-1275. The North Dakota State Seed Department analyzes seed for germination percentage. Contact the department at (701) 239-7210.
Clean disease-infected grain before using for seed. Saved seed with germination of 80 to 90% should be treated with a fungicide seed treatment before planting. Most standard seed treatment fungicides may significantly improve germination and emergence of scab infected wheat.
Realize, however, that although a seed treatment before planting will improve seed germination and seed vigor, it will not prevent subsequent head scab infection. Spores of the Fusarium fungus are carried through the air to infect the flowers or developing kernels of the head; the infection does not move up from infected seed.n
Information from Robert Stack and Marcia McMullen, NDSU plant pathologists. For World Wide Web information on scab in small grains, check out the NDSU web site: http://www.cc.ndsu. nodak.edu/instruct/stack/FHB/FHB.html
Western Canada could be first for Roundup-ready wheat
Western Canadian farmers could become the first in the world to grow Roundup Ready wheat under a new agreement between Monsanto and Agriculture Canada. The multi-year joint research agreement will see the technology that makes a crop resistant to Monsanto's herbicide Roundup inserted into Canada Western Red Spring Wheat lines at the federal government's Winnipeg Cereal Research Centre, according to the Manitoba Co-operator.
Under the deal, researchers will share technology and project expenses, which are expected to be around $2 million. Some of the funds will come through the federal government's Matching Investment Initiative, under which taxpayers match research investments made by the private sector.
David Torgerson, executive director of the Minnesota Wheat Research and Promotion Council, points out that wheat producers in the northern U.S. could benefit from the agreement.
"If Monsanto were to develop a similar program in the United States, it would likely be winter wheat, the largest wheat class and thus a larger market. Northern U.S. producers have grown Canadian varieties, such as AC Domain, so U.S. spring wheat producers might benefit, depending on licensing and production rights under the agreement," he says.
Roundup-ready wheat for Canada only, however, would definitely give Canadian farmers a production advantage over U.S. spring wheat producers.
"It is important that we work with biotechnology companies to make sure U.S. spring wheat producers have access to the same technology that other wheat producers have. It may even offer an opportunity for our two countries to work more closely together on market access," says Torgerson.n