A new race of wheat rust, Ug99, has overcome many of the resistant genes that have been saving wheat varieties since the 1950s. The rust is spreading quickly through southern Asia and the potential for the disease to move into North America is high.
June 10, 2008
1950s, resistance genes bred into wheat varieties have held truly devastating
stem rust epidemics in check. However, a new race of the rust, Ug99, has
overcome many of those resistance genes and is marching east through southern Asia.
appeared in Uganda wheat in 1999 and
spread to Kenya and Ethiopia during the next few
“At that point,
many international scientists said, ‘This is something we need to check because
this new race can overcome many of the effective resistances,’” said David
Marshall, research leader with the USDA-ARS in North Carolina last spring.
included the resistances that are in the international germ plasm out of the
International Maize and Wheat Improvement Center near Mexico City. That’s alarming and
this rust has become a front-burner issue.”
The spread of
Ug99 through east Africa “raised a red flag and the USDA, in cooperation with
CIMMYT and other international breeding centers, set up a program to identify
germ plasm worldwide, based on how it fares — resistant, intermediate, or
susceptible — with the new rust race,” said Marshall.
done in large part with the Global Rust Initiative (see
www.globalrust.org/), continues to move forward.
so does Ug99. By last year, the rust had leapt from Africa into Yemen. Now confirmed in Iran, wind patterns suggest
Ug99 could have also reached the northern Middle East, Afghanistan, India and Pakistan. Some 20 percent of the
world’s wheat is grown in India and Pakistan.
“One of the
interesting factors that Iran has introduced to the
situation is barbary bushes, an alternate host for the stem rust fungus,” says
Gene Milus, University of Arkansas professor and wheat
pathologist. “That means Ug99 will likely hybridize with the stem rust isolates
that are native to Iran.”
isolates coming out of Iran will probably be
different than the Ug99 that went into the country.
“That’s due to
the sexual recombination and will mix up the genotype. If indeed that happens,
the thinking is there may be even more resistance genes overcome by new races
coming out of Iran.”
varieties being grown in Afghanistan are susceptible to
Ug99. Even though there isn’t huge wheat acreage there, many Afghanis — as with
African producers — are subsistence farmers.
could really mess things up in that region of the world,” says Milus. “Adding
another volatile element in that area could destabilize it even further. No one
new stem rust will end up in the United States.
“Will it arrive
on the trade winds — we get winds out of China, across the Pacific Ocean and into the United States. Or will it arrive via
clothing? Obviously, there is a lot of traffic between the United States and the Middle East these days. There is a
serious possibility this rust could arrive aboard an airplane,” says Jim
Peterson, wheat breeder at Oregon State University and chair of the
National Wheat Improvement Committee.
“We don’t know
how much time there is before it’s found here. Months? A decade? But it is
multiplying and moving well with the aid of susceptible wheat varieties.”
worry is with wheat in the subcontinent. At least 75 percent of the region’s
major production area is susceptible to Ug99.
“It is critical
to get new disease resistances integrated into their varieties and deployed as
quickly as possible,” says Peterson. “If that doesn’t happen, there could be
serious food shortages in those areas.”
The NWIC represents
U.S. wheat researchers. “We
try to communicate to federal agencies, Congress, and USDA our concerns
relative to wheat issues,” says Peterson. “That includes everything from
marketing to diseases to import/export dynamics, whatever.
“As you can
imagine, Ug99 has been a top concern of ours and the National Association of
Wheat Growers for several years. We’ve continued to communicate those concerns
to Congress and ARS to try and promote research funding to address this
critical vulnerability in the United States and around the world.”
Unfortunately, U.S. funding is largely
is certainly taking a leadership role in addressing this exposure. They’ve
sponsored and funded screening of U.S. material — germplasm,
varieties, experimental lines — in Kenya over the last three
That work has
produced a “tremendous data set” to understand both vulnerability and what
resistances can be deployed against the rust.
good news. The bad news is we’ve been going to Congress for the last three
years trying to raise awareness of Ug99 and promote additional funding for both
ARS and state research programs that breed wheat varieties. State pathologists
are included in those efforts, obviously.
“Our efforts to
increase funding have so far been unsuccessful. We’re optimistic growing
awareness — along with recent, acute concerns over world food security — might
spur additional research funding.”
Does the new
farm bill provide any funding? “The ink on that is still wet,” says Peterson.
“But to my knowledge, it doesn’t. The word is there’s been no infusion of funds
into this rust research.”
disappointed that Congress doesn’t understand what’s at stake with the disease.
“On top of everything, our government has cut USAID (United States Agency for
International Development) funding for just this sort of work. For this fiscal
year, 2008, the money that’s been providing base support for international
research centers — not just for wheat, but all crops — has been cut to zero.
Congress cut next year’s funding, as well.”
shortsighted in the extreme, insists Milus. “The disease can be erratic but
under the right environmental conditions, there can be 100 percent loss in
infected fields. It can be devastating.”
Both men laud
the Bill and Melinda Gates Foundation, which pledged $26.7 million towards
monitoring and combating the rust for the next three years.
is a critical message to others about how important this is and how exposed
many developing nations are to Ug99,” says Peterson. “There are solutions,
here. From our standpoint, scientists need resources available so we can
respond quickly. That’s been a big challenge, thus far. I hope timing is in our
favor,” says Peterson.
A bit of
historical perspective: until the 1960s, stem rust was a major disease in the Midwest. Some years, 30 to 50
percent of North Dakota’s wheat crop was lost
to the disease.
major portion of the world’s wheat has a high vulnerability to the disease,”
says Peterson. “Fungicides can be of help, but they aren’t a silver bullet —
particularly in developing nations that have difficulty accessing fungicides,
much less applying them.”
And how in a
developing nation could vast wheat acreages be treated? Not many countries have
aerial applicator fleets.
“The fear is
we’ll have a year when the environment is perfect for the disease and it takes
off. I don’t know how small farmers would be able to stay ahead of it — even if
the fungicides are available to them.”
circumstance, jugs of fungicides could be sitting outside farmers’ doors, “but
do they have the means, infrastructure and education to apply fungicides at the
proper time, proper stage of development? Perhaps they could minimize the
damage, but it is certainly unlikely they could eliminate the disease
are spraying fungicides two or three times during the wheat growth cycle.
“They’re under intense rust pressures — stem rust first, but also leaf and
stripe. So, they have to use high levels of fungicide just to get a crop. That
should be a warning to everyone.”
As it was in
the 1950s, the answer to the new stem rust is variety resistance.
“UG99 took out
many of the core resistance genes we’ve relied on for decades. That has left us
extremely vulnerable. There are a small number of genes still effective. Right
now, the strategy is to, as quickly as possible, move those into adapted
varieties and get them into farmers’ hands.”
International Maize and Wheat Improvement Center (CIMMYT) is “working
frantically” to do just that, says Milus. “They have a small number of
experimental lines already on seed increase with genes they think will provide
effective resistance. They’ll deploy those in India, Pakistan and parts of Africa. But it takes time.
Just to increase seed stocks to cover a couple of countries takes two or three
rust’s movement is very tricky, says Peterson. There have been attempts to
match up information on wind flow and the disease’s progress out of Africa.
done a tremendous job predicting movement based on wind flow. But one event can
throw everything off. Last year, one major wind event essentially moved the
rust from Yemen into Iran. “
wind events have since been recorded that “could have already moved the disease
into India and Pakistan. That isn’t a definite
— and nothing has been found on the ground. But the model says it’s possibly