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United States Department of Agriculture

Agricultural Research Service

Christina Cowger
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Dr. Cowger investigates the biology, epidemiology, and population genetics of economically important small grain pathogens. Her goal is to contribute to improved, sustainable management practices. Her program interacts closely with breeders, extension personnel, and other pathology and population genetics groups in the U.S. and beyond.
Dr. Cowger has expertise in pathogen adaptation to host resistance; host genotype diversity and its effects on pathogen populations; small-grain disease diagnosis and management; and epidemiological and management implications of pathogen population structure.  Her group conducts research in the laboratory, greenhouse, and at multiple field locations. The lab uses molecular techniques to investigate species identity, phylogeny, population structure, and pathogen life cycles. Epidemiological modeling and classical field-plot research are also carried out.

Three examples of current research:

* Little is known about the population structure of Blumeria graminis f. sp. tritici, cause of powdery mildew of wheat. Powdery mildew is a chronic problem in the eastern U.S. and can inflict substantial economic losses on soft red winter wheat producers. Cowger’s lab is learning about the mildew population in order to design more effective management strategies.  Researchers develop and use virulence profiles of mildew isolates to facilitate breeding for resistance.  Our group analyzes molecular variation among mildew isolates to learn about gene flow and population subdivision, using both classical and new, genealogy-based population genetic approaches.

*Stagonospora nodorum blotch is a disease of wheat leaves and heads that reduces test weights and may infect grain, potentially causing disease problems the following year if the seed is replanted.  The fungus has recently been shown to produce a large suite of host-selective toxins (HSTs), which have a toxic effect when they interact with specific genes in the wheat plant that may be conferring resistance to a completely different disease.  Cowger’s group is getting a picture of HSTs and the wheat genes they target in the Southeastern U.S.  This will help determine whether breeders in the region can and should “breed out” sensitivity to these toxins.  Cowger is also working collaboratively to determine how much of an effect on yield and test weight SNB has, and consequently where to set thresholds for profitable fungicide application.

* Fusarium head blight (scab) is a potentially devastating disease caused by the fungus Fusarium graminearum (= Gibberella zeae).  The fungus produces mycotoxins, including DON and nivalenol, in the heads of wheat and other small grains. Even low concentrations of DON, or "vomitoxin," cause serious digestive problems in livestock and humans. Cowger’s lab receives funding from the U.S. Wheat and Barley Scab Initiative to help clarify what makes for a severe scab outbreak.  The group is collaborating with other USWBSI-funded researchers to investigate the effects of extended post-flowering moisture on disease and toxin development in cultivars with different levels and types of resistance.  Other studies focus on the results of late (post-flowering) infections, and the use of both cultivars and fungicides to manage disease.

Last Modified: 4/12/2013