Castroville, Texas
May 28, 2009
Standing as a sentinel for rust
issues that can affect wheat from South Texas to Canada is a
field nursery operated by Texas AgriLife Research just east of
Castroville.
Dr. Jackie Rudd of Amarillo and Dr. Amir Ibrahim of College
Station, both AgriLife Research wheat breeders, work with
researchers from throughout the Great Plains to test varieties
for rust resistance, primarily on leaves.
While Ug99, a new stem rust causing concern around the world,
has garnered the most attention lately, leaf rust is actually
with Texas producers every year, Rudd said. It was rated as the
top disease affecting wheat statewide in a recent survey of
producers.
 “What
we have here is a multi-state screening nursery for leaf rust,
and we hope we don’t have to use the same nursery for screening
for stem rust, which is a serious disease that we’ve had a
handle on for the past 50 years,” Ibrahim said.
Ug99 broke that 50-year resistance record when it first appeared
in Africa in 1999. The rust has followed a path predicted by
scientists through east Africa and now is in Kenya, Uganda,
Ethiopia, Sudan, Yemen and Iran. This has led to concern that it
might reach the U.S.
“We don’t want to see it at our back doors, so we are developing
a plan of action,” Ibrahim said. “We have a proactive approach
to deal with it.”
He said they are working mainly through host-plant resistance
and developing lines with good resistance to it.
“We send lines to be tested in Kenya where the disease is,”
Ibrahim said. “We use molecular markers to screen against it. We
have varieties in the pipeline that are resistant to Ug99, and
they are under seed increase. So we are ready with those
resistant varieties.”
He said there also is a need to develop a fungicide application
package and a plan of mitigation in case this race comes to
Texas and in case that longtime resistance breaks at any time.
Different types of rust diseases attack under different
environments in the various wheat growing regions, Rudd said.
For the last 10 years, leaf rust has caused an average of 5
percent yield loss every year in Texas, but it generally doesn’t
kill the entire crop, he said. It’s very important to producers
to grow resistant varieties, but it is not devastating in any
one year.
 Stripe
rust is a disease Texas didn’t even have until 2001, Rudd said.
“We started seeing it then, and 2003 was a bad year,” he said.
“In 2005, Texas producers lost almost 15 percent of their wheat
crop due to that one disease.”
Stem rust can be even more devastating, Rudd said. It’s one that
doesn’t just cause yield reduction, but can destroy entire
fields.
The nursery at Castroville is grown to identify varieties with
resistance and susceptibility, he said.
Wheat varieties such as TAM 112 do great in the High Plains
because that region doesn’t get leaf rust every year, but it is
not recommended in the rest of Texas because it is susceptible
to leaf rust and stripe rust, Rudd said.
“On the other hand, TAM 203 is nice and clean with a very good
resistance to all the rusts,” he said. “The nursery in South
Texas is important because that is how we are able to identify
things like that, because every single year there is rust.”
The significant thing about South Texas is that often rust that
begins there will often move up with the winds and maturity of
the crop into northern Texas and into Oklahoma and all the way
to Manitoba, Canada within a single season’s time, Rudd said.
“So Texas often gets blamed for causing epidemics throughout the
Great Plains,” he said. “We have to really work hard to keep a
high level of resistance in Texas, not only to protect the Texas
producers, but the entire Great Plains.”
The nursery at Castroville was started in 2000 by Dr. Alan
Fritz, a wheat breeder at Texas A&M University at the time. It
has grown from less than 1.5 acre to about 20 acres, and
involves about10 universities, mostly from the Great Plains, all
looking at the leaf rust, Rudd said.
“It’s a great nursery for identifying susceptibility and
selecting for resistance,” he said. “The nursery has yield
trials to look at the yield production and also populations so
we can find resistant material for the next generations. There
are more than 10,000 different genetic rows of wheat that we
evaluate every year here.”
Rudd said when he started in 2002, only 20 percent of Texas A&M
varieties were resistant to leaf rust. Right now, 80 percent of
the TAM material is resistant, “so we’ve made a lot of gains
through nurseries like this.”
In the area of stripe rust, a lot of ground has been gained in
the last few years and most of the TAM varieties are resistant
to stripe rust also, he said.
But the wheat breeders’ job is not done. A resistant variety
often becomes susceptible in a few years because of changes in
the pathogen, Rudd said. Breeding programs are changing their
strategy and beginning to breed for durable rust resistance.
The type resistance involves multiple genes and was very
difficult to breed for until recent advances in molecular-marker
technology, he said.
“Stem rust demonstrates the on-going battle between breeders and
pathogens,” Rudd said. “We’ve had total resistance for the last
50 years, but with Ug99 that has changed. Now we have to change
our focus.
“Since we don’t have Ug99 in the U.S., we don’t have stem rust,
so we can’t use a nursery like this,” he said. “We use molecular
markers and send material over to Kenya to screen for
resistance, rather than bring the disease here. We don’t have it
here, and we don’t want it here.” |
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