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Researcher takes new approach with wheat leaf rust resistance

Agriculture.com Staff 12/10/2008 @ 10:03am

Sometimes less is more. That's how Kansas State University (K-State) 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 says.

"Leaf rust long has been one of the biggest concerns for wheat breeders in Kansas and the Great Plains," he says in a university report. "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 says.

"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 says.

Some of the minor genes for leaf rust resistance also carry minor gene resistance for stripe rust, Fritz adds. 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 says.

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

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