Pests tend to be good travelers.
Consider the gypsy moth, an insect that defoliates trees while in its caterpillar stage; tansy ragwort, a toxic weed that infests pastureland; or eastern filbert blight, a disease that kills filbert trees. These are a few examples of destructive pests that traveled thousands of miles to get to Oregon.
Unfortunately for Oregon's barley growers, a plant disease called barley stripe rust may be the best traveler of them all. Some pests get around as hitchhikers or stowaways on agricultural crops transported via truck, train or ship from one place to another. Barley stripe rust doesn't bother with ground transportation. This pest prefers to fly.
According to Chris Mundt, Oregon State University plant pathologist, barley stripe rust is able to move long distances in relatively short periods of time because it travels on the wind just like many other fungal plant diseases. However, this disease can travel hundreds or even thousands of miles on the wind, making it a particularly good air traveler.
"Spores of the disease have thick walls that are resistant to temperature extremes," said Mundt. "The spores are well-adapted for survival in the upper atmosphere so they can be blown long distances by prevailing winds at high altitude and still be viable after falling back to earth."
But the mobility of this disease is just the beginning of the bad news.
"Explosive," "devastating," "horrific," "capable of inflicting enormous damage," "most serious disease threat in the region"-these are some of the ways scientists and industry experts have described barley stripe rust.
Depending on weather conditions, the disease varies from year to year and even from field to field in how destructive it may be. However, since its arrival in Oregon nearly a decade ago, barley stripe rust has caused millions of dollars in crop losses. Oregon growers produced over eight million bushels of barley in 1998, worth $12 million. Oregon production fell in 1999, but was back up to 8.4 million bushels in 2000.
"The year 2000 was the worst I've had for crop damage caused by barley stripe rust," said Lynn Long, a Klamath Basin grower. Long raises barley crops on 1,900 acres near Klamath Falls. "It seems as though the severity of the infestations is getting worse and worse. It's an increasingly difficult problem."
The stripe rust fungus acts like a parasite while it grows on plant leaves, breaking into plant cells and robbing the host plant of nutrients and moisture. The fungus produces large numbers of spores every day so as the disease grows and spreads, it gradually stunts the host plant more and more.
Barley plants infected with barley stripe rust become weakened and tend to produce smaller kernels than healthy non-infected plants. Widespread infections seriously reduce barley yields and kernel quality to the point that grain quantity and quality drops off significantly.
In response to the threat, a group of OSU agricultural scientists and extension educators, in cooperation with the Oregon Grains Commission and international barley researchers based in Mexico, began coordinating efforts early in the 1990s to help Oregon barley growers fight the disease.
The group, known as the barley stripe rust team, includes Chris Mundt, OSU plant pathologist; Pat Hayes, OSU barley breeder; Randy Dovel, formerly an agronomist at OSU's Klamath Falls Agricultural Experiment Station; Rod Todd, OSU Extension Service agent in the Klamath County Extension office; Russ Karow, OSU Extension Service cereal crops specialist; Hugo Vivar, barley breeder with the International Maize and Wheat Improvement Center in Mexico; and Tammy Denee, administrator with the Oregon Grains Commission, Pendleton.
They conducted a two-part strategy involving short-term and long-term solutions. In the short term, team members worked with growers and the commission to identify fungicide controls to prevent barley stripe rust infections. Growers have also tried to avoid barley stripe rust by growing less susceptible barley varieties. The long-term approach focused on developing stripe rust-resistant barley varieties.
Mundt had been keeping a wary eye on the disease since the early 1990s and was the first to warn growers and the Oregon Grains Commission about it. Given barley stripe rust's unique ability for high-altitude air travel, Mundt's vigilance was well justified.
After moving north from South America to Mexico in the 1980s, the disease crossed the U.S.-Mexico border in 1991 and decimated barley crops in Texas. It appeared in Colorado the following year and from there apparently blew over to California's Sacramento Valley.
In 1995 the disease was reported in every state of the western United States and caused commercial-scale losses of barley production in several areas including the Klamath Basin.
The Oregon Grains Commission provided crucial early support in the battle against barley stripe rust, according to Mundt.
"We [Mundt, Pat Hayes and Russ Karow] met with the commission to talk about the problem a few years before the rust actually got here," said Mundt. "The commission has limited resources for research grants, but decided to fund OSU research on the problem. Looking back now, it turned out to be a very good decision."
Sam Henzel thinks the decision was a lot more than good. He believes Mundt's early warning and the commission's response to it were crucial to southern Oregon's barley industry.
"The five- or six-year advance warning we received saved the industry here," said Henzel, Klamath Basin barley grower and co-owner of Tri-Cord elevators in the lower Klamath Lake area. "This area's first serious infestation was in 1995. The grains commission getting involved early on, along with OSU, was the most important thing. It prevented the situation from getting into horrific losses."
Most Oregon barley production is in the south central part of the state-Klamath County-and northeast Oregon-Sherman, Gilliam and Umatilla counties. Growers produce feed barleys for livestock and malting barleys for use in the brewery industry. Malting barleys have higher market value, but feed barleys comprise most of Oregon's barley production.
Barley stripe rust hit Klamath Basin growers much harder than the barley growers further north. This happened for two reasons, according to Karow.
"First, the cool, moist spring weather conditions of the Klamath Basin are ideal for the disease," Karow said. "And second, most Klamath Basin growers plant barley annually, which helps the disease survive in the field year after year."
Growers in the northern counties often plant barley in rotation with winter wheat crops. Planting barley in a crop rotation breaks the life cycle of the disease, making it harder for stripe rust to survive in the same area from year to year.
The disease's hardiness helps it survive through several generations in one growing season, which, in turn, helps it spread rapidly, Karow explained.
"When barley stripe rust first hit the Klamath Basin, many producers were growing the six-row type barleys, which are generally feed barleys," said Todd.
All barley varieties fall into two categories: two-row barleys and six-row barleys. Two-row barleys have a row of kernels on either side of the main plant stem. Six-row barleys have three rows of kernels on either side of the main plant stem.
"The six-row types were very susceptible to the disease and many growers switched to two-row varieties, which seem to be less susceptible," said Todd. "It's not the best answer to controlling the disease, but switching varieties has helped some growers avoid serious losses."
Todd's role on the stripe rust team is to coordinate local educational efforts in the Klamath Basin. He set up workshops and field days to deliver information on the disease to growers and industry representatives.
"Until we get a better long-term solution such as a truly good variety agronomically [good yield potential and kernel quality], as well as having the resistance that is necessary, the problem won't have gone away," Todd said.
J.W. Cope, barley field representative with Winema Elevators near Merrill, Oregon, agrees.
"The ultimate solution will be either we won't grow barley or we will have to grow resistant or tolerant varieties," Cope said. "The disease has had a huge impact here, more than any other barley producing area that I know about."
Pat Hayes, OSU barley breeder and team member, has led the variety development effort. He worked closely with team members, growers, the grains commission, and international barley breeders in his search for parent barley varieties to use in advancing new stripe rust-resistant progeny.
"We were able to get an early start with the resistant varieties program because of support from the Oregon Grains Commission and a good working relationship with many researchers in the International Center for Agricultural Research in the Dry Areas (ICARDA)," said Hayes. "The ICARDA connection is important because scientists with that group have been working on the barley stripe rust problem for a long time and they already have stripe rust-resistant plant material."
Hugo Vivar, barley breeder and Latin American program coordinator for ICARDA, provided Hayes with disease-resistant plant material in the early stages of the variety development project. Vivar is now retired but continues to work with Hayes as a consultant.
The barley stripe rust resistance project came along at a good time, said Hayes.
"In 1991, when we first began talking about this, I had already been involved in the barley genome mapping effort for several years," Hayes said. "The push to come up with stripe rust-resistant barley varieties proved to be an excellent opportunity to use this gene-mapping technology in basic plant breeding to develop a new variety growers wanted."
The barley genome-mapping project is a cooperative effort involving several land grant universities and barley industry associations. Scientists and industry officials undertook the project in the hope that mapping the barley genome would allow barley breeders to develop improved barley varieties with specific characteristics such as high yield potential, disease and pest resistance and cold hardiness. The project began in 1985 and is ongoing.
A genome, or gene, map is a graphical representation of an organism's genome, or set of genes that the organism passes on to progeny. The map shows where specific genes are located, relative to each other, on a chromosome (see related story). Scientists are currently conducting a wide variety of genome mapping projects. For example, scientists have been working on the mapping of the human genome over the past several years.
However, back in the 1980s when Hayes, in concert with colleagues from several other land-grant universities, started their project with the barley genome, the whole idea of gene mapping was radically new.
"Many plant breeders were skeptical about the practical use of gene maps in breeding projects back in the 1980s," Hayes said, "and some breeders still are not completely convinced that gene maps are useful."
Hayes, however, believes that the development of the stripe rust-resistant barley variety Tango makes a strong case for the role gene mapping can play in plant breeding.
Tango is the first barley variety produced by the OSU barley breeding program in response to the stripe rust threat. It is also the first publicly released commercial crop variety in the United States and the world, to Hayes' knowledge, to be developed with the assistance of marker-assisted selection, an application of gene mapping technology.
So what is the advantage of using this technology in the development of new plant varieties? Hayes said gene maps save time and allow breeders to identify genes that are responsible for a particular characteristic.
Hayes and his colleagues began working on the variety that eventually became Tango in 1989. It was officially released to growers in 2000. That's 10 years from greenhouse to the grower's field. It may not sound like a big deal, but it is to a plant breeder.
"Usually it takes 12 to 15 years to get a new plant variety developed and released," said Hayes. "The use of gene maps saved a lot of time in the first three to five years when, in a traditional breeding project, breeders have to field test all the progeny (which may be hundreds or thousands) from parental crosses, evaluate them for disease resistance and discard those that appear susceptible. With gene maps, we were able to identify and concentrate our efforts on just those progeny that had the resistance gene."
Hayes describes the development of Tango as a great example of a basic nuts- and-bolts application of gene mapping technology. He added that gene mapping doesn't involve any of the controversial gene technologies such as transgenic techniques used to develop genetically modified organisms.
"We could have developed Tango without the aid of gene maps, but having the maps enabled us to know which gene makes Tango resistant to barley stripe rust," said Hayes. "This knowledge will allow us to develop new varieties that possess Tango's stripe rust resistance characteristic in an even shorter time period. Tango required 10 years of development. Newer, better varieties may take six to eight years to develop. It is the ability to locate and identify genes for resistance that makes this possible."
The downside, Hayes continued, is that Tango is not a great variety in terms of grain yield and kernel quality.
The Tango variety isn't the best answer to Oregon's barley stripe rust problem, but Hayes believes the development of Tango proved an important point.
"We've shown that gene technology can play a major role in our efforts to develop barley varieties that will more closely satisfy grower requirements," he said.
Lynn Long is confident that Hayes and his colleagues will deliver.
"The development of new varieties is a work in progress and I believe we will see some good varieties released," said Long. "The challenge for Hayes and his breeding group now is to come up with a variety that is resistant to barley stripe rust and that has good agronomic characteristics, or in other words, something that will deliver a good return to growers."
|GENE MAPS HELP BREEDERS|
A genome is an organism's complete set of chromosomes. And, if you'll recall from your high school biology course, chromosomes contain the genetic material that determines the characteristics of all living things. Chromosomes occur in pairs within cells and all organisms have a particular number of pairs of chromosomes. Humans, for example, have 23 pairs of chromosomes. Barley plants have seven pairs.
Chromosomes are linear in form, and for that reason, so are gene maps. A gene map is a vertical line with loci (intersecting lines along the axis of the vertical) indicating where particular genes are located on the chromosome.
Gene maps allow plant breeders to establish the relative location of genes of interest-in this case genes for barley stripe rust resistance. Scientists do this by identifying other genes adjacent to the gene of interest. The second step is important because genes are usually passed from parent to progeny in groups.
"Any particular gene is always linked to other genes on any chromosome," said Hayes. "Therefore, when we cross parent plants to get a gene for resistance in the progeny, we know genes for other characteristics will come along with a resistance gene."
It's generally possible to identify at least one of the genes associated with the gene of interest using laboratory processes called electrophoresis and DNA sequencing.
"The ability to identify genes associated with, or linked to, desired genes is what makes gene mapping a valuable tool," said Hayes. Breeders use the identifiable genes as markers-often called molecular markers-that they look for in progeny from parent crosses. This process is referred to as marker-assisted selection.