On BarleyA Rust of Another
Agronomist Darrell Wesenberg inspects barley test plots for early-season
incidence of barley stripe rust.
When barley stripe rust started powdering plants and sapping yields in the
Pacific Northwest in 1995, USDA's Agricultural Research Service was as ready
as could be under the circumstances. Agency scientists knew they were facing a
new fungal disease. They also knew that farmers had no resistant barley variety
and no adequate fungicide registered to fight it.
Many of themlike ARS plant pathologist Roland F. Line, an
international expert on a similar disease that affects wheat, and ARS
agronomist Darrell M. Wesenberg, an expert on barley breedinghad followed
the spread of barley stripe rust from Europe to South America in 1975 and to
the United States in 1991. David Marshall of Texas A&M University first
observed the rust in Texas.
Line and Wesenberg are part of a broad effort to rein in the disease. Line
is based at ARS' Wheat Genetics, Quality, Physiology, and Disease Research Unit
in Pullman, Washington. Wesenberg is in the ARS Small Grains and Potato
Germplasm Research Unit at Aberdeen, Idaho.
Their cooperators include other ARS researchers in Aberdeen, Pullman, and
St. Paul, Minnesota; scientists at Centro Internacional de Mejoramiento de Maiz
y Trigo, or CIMMYT, an international organization headquartered in Mexico; and
state university scientists and private breeders throughout the western United
Natural Resistance, a First Defense
The researchers' teamwork to ward off the threat has focused primarily on
exploiting the genetic rust resistance already present in wild and cultivated
strains of barley plants.
A severe barley stripe rust infection can severely dehydrate plants and ruin
the barley crop.
The researchers have now developed some new, conventionally bred resistant
barley. More varieties will arrive soon. And genetic engineering offers the
possibility of more strongly resistant varieties for farmers in the future.
Barley stripe rust spreads by powdery, yellow spores. The spores are
produced in large, yellow stripes between leaf veins, giving the leaves a
striped, rusty appearance. The fungus may rapidly cover the leavesand
even the barley headand effectively suck the plant dry.
"The rust causes rapid water loss, creating a drought for the plant no
matter how much water is available," says Line.
The disease reached the Northwest's "backyard" in 1993, turning up
in Arizona, southern Idaho, and Montana. It was then that Line started working
under controlled conditions in the greenhouse with rust collections from the
regions where barley stripe rust occurred in North America.
Line artificially infected plants from ARS' gene bank in
Aberdeenformally known as the National Small Grains Collection. He used
DNA identification techniques and pathogenicity studies to show that the barley
rust was "clearly different from wheat stripe rust, but closely
By 1995, Line confirmed what scientists had feared: The barley pathogen,
like its wheat stripe rust cousin, was favored by cool, wet springs and mild
winters. "Unfortunately, that meant the Pacific Northwest and California
were tailor-made for it," he says.
Line has received reports of plants in California fields being so damaged
that they weren't worth harvesting. "Wherever this disease shows up and is
not controlled, it causes significant to severe damage at times. When severe,
yield losses of 50 percent are not uncommon," he says.
More bad news: Line and Xianming Chen, an associate in his lab at Pullman,
determined that the rust consists of at least 31 different races or strains.
This means it could attack a wide range of barley varieties and easily create
new races that might attack new resistant varieties that are developed.
Plant breeders rely on sources such as ARS' National Small Grains Collection
for materials for improving crops. Here, agronomist Charles Erickson selects
barley accessions for evaluation.
By 1996, the fungicide Folicur became available to growers under an
emergency authorization by the U.S. Environmental Protection Agency (EPA). Line
provided research data that farmers and pesticide companies used in requesting
the EPA approvalgranted on a year-by-year basis. Line had found that
Folicur protected barley late into the season, throughout all its vulnerable
stages. He had also determined that at least two other fungicides are
effective, and he is part of an effort to make them available, too.
Identifying the Resistance Genes
Line and Chen identified many sources of rust resistance in the Aberdeen
collection. By making many crosses with susceptible varieties and among the
resistant sources, they identified 26 genes for resistance. They also found
which genes are common in the resistant sources.
Rust-resistance genes are now easier to locate, because of a new technique
Line and colleagues developed for finding molecular markers linked to rust
"It's a real breakthroughfaster, more efficient, and less
expensive," says Line. "It yields more markers, and it is directly
associated with resistance genes." This technique is currently being used
in cooperation with Patrick M. Hayes, a barley breeder at Oregon State
University, to breed for adult plant resistance to the rust and other diseases.
To find barley with natural resistance to the destructive rust, ARS
researchers at Aberdeen, Idaho, have meticulously screened hundreds of plants
from the nation's barley gene bank at Aberdeen and elsewhere.
They did the work with Colorado State University and Bolivian scientists.
Colleagues at Colorado State included plant pathologists William M. Brown, Jr.,
Joseph P. Hill, and Vidal Velasco.
ARS agronomist Harold E. Bockelman manages the Aberdeen gene bank that also
houses wheat, oats, rye, and other small grains.
Field evaluations began in 1990 in Cochabamba, Bolivia. That location was
chosen because the fungus was severe there, causing losses of 30 to 70 percent.
"We started testing for stripe rust resistance before it showed up on any
American farms," says ARS agronomist Darrell Wesenberg, "because it
seemed likely the rust would eventually make its way into the United
At the Bolivia trials, the scientists identified several rust-resistant
plants. A star performer was number 78Ab10274, a product of the ARS barley
breeding program at Aberdeen. Later, 78Ab10274 also did well in trials at
Toluca, Mexico, which had by then become another site of severe rust
infestation. Hugo Vivar directed the Mexico trials for CIMMYT.
Tests in Idaho and several other western states showed that 78Ab10274
yielded as many bushels as most leading commercial varieties of spring barley.
Scientists gave it the name "Bancroft" and expect to formally release
it for commercial production this year.
Though tests have so far focused on Bancroft's performance as a feed barley,
ARS scientists are also conducting field-scale trials to evaluate its potential
for malting and brewing.
To introduce antifungal genes into barley, biological research technician
Robert Campbell places barley tissue into the vacuum pressure chamber of a
Engineering Better Barley
New techniques for gene-engineering barley may augment conventional breeding
like that used to produce Bancroft and may hasten development of additional
rust-resistant barley for the future. Biotechnologists Shibo Zhang, Myeong-Je
Cho, and Peggy G. Lemaux of the University of California and ARS geneticist
Phil Bregitzer at Aberdeen have come up with a new and better way to sidestep
some of the problems that can occur when researchers try to slip new
genessuch as genes for disease resistanceinto barley cells.
Instead of moving the genes into plant embryo tissuea common
approachthe scientists recommend using what's known as cultured
meristematic tissue, which is derived from the growing tip of the plant. They
say this tissue is less likely to incur changes in its genetic makeup when it
is bombarded by a gene guna device that shoots gene-coated particles into
Also, successive generations of plants derived from laboratory-cultivated
meristematic tissue are less liable to develop natural differences, or
mutations, known as somoclonal variation. Though desirable in some types of
plant breeding, somaclonal variation can disrupt genetic engineering
What's more, embryonic tissue sometimes yields albino plantlets, while
meristematic tissueif cultivated according to lab procedures developed by
the scientistshas a better chance of yielding fertile, green, healthy
plantlets. Zhang, Cho, Lemaux, and Bregitzer are seeking a patent for their
discoveries.By Don Comis
and Marcia Wood, Agricultural
Research Service Information Staff.
This research is part of Plant Diseases, an ARS National Program
described on the World Wide Web at
Roland F. Line is in the
USDA-ARS Wheat Genetics, Quality,
Physiology, and Disease Research Unit, 361 Johnson Hall, Washington State
University, Pullman, WA 99164-6430; phone (509) 335-3755, fax (509) 335-7674.
Darrell M. Wesenberg and
Phil Bregitzer are in the
USDA-ARS Small Grains
and Potato Germplasm Research Unit, 1691 S 2700 W, Aberdeen, ID 83210;
phone (208) 397-4162 [Wesenberg ext. 108, Bregitzer ext. 116], fax (208)
"On BarleyA Rust of Another Stripe" was published in
the August 1999 issue of
Agricultural Research magazine.