Fusarium Head Blight of Wheat

Introduction

Fusarium Head Blight (FHB), also known as head scab, caused by Fusarium spp., has historically been a devastating disease of wheat and barley around the world. In the 1990's losses in excess of 3 billion dollars to the US wheat industry and concerns over food safety led to the establishment of the US Wheat and Barley Scab Initiative. Funds appropriated by Congress are being used to support research in more than 20 states, including Kentucky, with the goal of stopping FHB from damaging wheat and barley crops. In Kentucky, fungal inoculum is readily availabe because prevalent cropping systems of no till or minimal till wheat production result in increased corn residue.  The benefits of these cropping systems make incorporating FHB resistance into soft red winter wheat the most effective control strategy.

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FHB Disease Life Cycle

Several species are capable of causing FHB.  In North America the species most commonly encountered is Fusarium graminearum.  Natural variation in F. graminearum exists but no races or specific strains have been identified.  In Kentucky, the primary source of inoculum comes from overwintering fungus colonies in remaining corn stubble.  The fungus produces perithecia on colonized corn stubble. These perithecia release ascospores into the air which infect the wheat or barley plant.  The plant is most susceptible to infection during flowering.  Symptoms caused by the fungus include premature bleaching of the spikelets or entire spike.  Seed from infected spikelets may be small, shriveled, and white or chalky in appearance.  FHB infected seeds are commonly referred to as tombstones. For more information, check the American Phytopathological Society (APS) lesson on FHB.

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Screening for FHB Resistance

An important part of the UK Wheat Breeding Program is development of wheat varieties with resistance to FHB. Screening for resistance is currently done in Lexington and Princeton, Kentucky. The Lexington FHB nursery is mist-irrigated and inoculated with scabby corn to optimize the conditions for infection. The Princeton FHB nursery is non-irrigated and inoculated with both scabby corn and a suspension of Fusarium graminearum spores. Wheat lines evaluated in the nurseries include early generation and advanced breeding material as well as material from multi-state collaborations. Resistance is assessed by symptoms (severity and incidence), Fusarium damaged kernels (FDK) and deoxynivalenol (DON) load.

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