Sometimes less is more. That´s how Kansas State University wheat breeder,
Allan Fritz, is now approaching the problem of getting durable leaf rust
resistance into new varieties.


Combining several resistance genes that, individually, impart only a minor
level of leaf rust protection to all races of leaf rust should offer more
durable resistance than using a single gene with very strong resistance to
specific races of rust, Fritz said.

"Leaf rust long has been one of the biggest concerns for wheat breeders in
Kansas and the Great Plains," he said. "In most cases, just as soon as wheat
breeders release a new variety with strong leaf rust resistance, a race of
leaf rust that can overcome that resistance comes along to attack the
variety."

To try to get ahead of this problem, Fritz is changing his approach. Instead
of focusing on strong, race-specific sources of leaf rust resistance, he is
now working with plant pathologists from the U.S. Department of
Agriculture´s Agricultural Research Service and CIMMYT (International Maize
and Wheat Improvement Center) in Mexico to incorporate so-called "minor"
genes for leaf rust resistance.

"None of these minor genes in itself provides strong resistance to leaf
rust. A variety minor gene resistance won´t be perfectly green during a leaf
rust outbreak. But there will be fewer leaf rust pustules, they´ll be
smaller, and they will take longer to develop on the leaves," he explained.

"When three or more minor genes for leaf rust resistance are combined, a
variety will have very acceptable resistance to all races of leaf rust. In
Mexico, varieties with minor gene resistance have maintained that resistance
for many years. That´s what we´d like to see in our new wheat varieties."

Fritz and his team at K-State have been crossing a genotype called "Amadina"
onto Overley, a hard red winter wheat variety. Amadina has four minor genes
for leaf rust resistance.

"We currently have 11 such lines in the Kansas Intrastate Nursery tests. If
all goes well with these experimental lines, we may have a new variety with
durable leaf rust resistance ready for release in 2011," he said.

Some of the minor genes for leaf rust resistance also carry minor gene
resistance for stripe rust, Fritz added. As a result, the new varieties
developed for minor gene, durable, slow-rusting leaf rust resistance will
also have the same type of durable resistance for stripe rust.

"If this type of durable leaf rust and stripe rust resistance can be
incorporated into most or all of our new wheat varieties, that will give us
more resources to focus on other traits in our breeding problem, such as
scab resistance, Hessian fly resistance, quality, and others," the wheat
researcher said.

K-State Research and Extension is a short name for the Kansas State
University Agricultural Experiment Station and Cooperative Extension
Service, a program designed to generate and distribute useful knowledge for
the well-being of Kansans. Supported by county, state, federal and private
funds, the program has county Extension offices, experiment fields, area
Extension offices and regional research centers statewide. Its headquarters
is on the K-State campus, Manhattan.

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