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David Marshall
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My research program focuses on understanding wheat-powdery mildew and wheat-rust pathosystems.  My research identifies genes for seedling and adult-plant resistance in contemporary cultivars and breeding lines.  New resistance genes are sought-out, identified, and introgressed into wheat germplasm adapted to those areas where the diseases are limiting factor to wheat production.  Molecular markers are being developed and utilized to facilitate marker-assisted selection for resistance genes in segregating populations and homozygous lines.  Research on the deployment of host diversity on local and regional scales emphasizes extending the useful life of disease resistance genes.

Specific objectives are: (1) Identify sources of resistance to fungal pathogens and introgress the resistance into adapted genotypes of cool-season cereals; (2) Breed and develop germplasm and varieties of hard winter wheat adapted to the humid regions of the southeastern U.S.; (3) Determine the effects of host genotypic heterogeneity on disease severity and yield; and 4) Develop and utilize molecular marker-assisted selection for disease resistance in cereals.


I have also overseen the breeding and development of specialty hard wheats for the humid areas of the eastern U.S.  We are collaborating with the North Carolina Organic Bread Flour Project. This project aims to link the farmer, the baker, and the miller in North Carolina with the goal of providing a viable market for organic hard and soft wheat and other small grains.

My program has identified many sources of resistance (especially to powdery mildew, stripe rust, leaf rust, and stem rust of wheat) that are available for breeders to incorporate into their specific germplasm and lines.

The first Winter Wheat Stem Rust Resistance Nursery, a key tool in the fight against the rust strain Ug99, has been established by ARS and international cooperators.

The nursery, established by ARS and the International Maize and Wheat Improvement Center(CIMMYT), is located in Ankara, Turkey, where CIMMYT coordinates its global winter wheat breeding program. It is the first of its kind for winter wheats, and is a joint effort to distribute 100 lines that have been identified by international scientists as having resistance to the deadly Ug99 stem rust and its descendants.

Thirty of the 100 lines in the nursery were developed by ARS scientists and contain resistance to stem rust races in Kenya and the United States. The lines developed by ARS focus on the use of four or five resistance genes that have been incorporated into various combinations in winter wheat lines. Multiple genes for resistance will slow the pathogen's ability to readily overcome the new wheat varieties that breeders develop. The amount of time these genes can remain effective is key to maintaining resistance to stem rust in the United States.

Nursery is New Tool in Fight against Ug99 Wheat Stem Rust
Agricultural Research Magazine, February 2010