A Visual Scale for Estimating Damage to Soft Red Winter Wheat Kernels by

Fusarium Head Blight

Jessica S. Engle, Erick D. De Wolf, and Patrick E. Lipps

A series of photographs showing different levels of kernel damage. Each photograph represents a certain percentage of affected kernels up to 100%.

A visual scale for soft red wheat was prepared by creating a grain sample with a known percentage of diseased kernels from the susceptible soft red wheat cv. Hopewell. Each sample contained a total of 200 kernels including a representative proportion of diseased kernels. The sample was then mixed and placed in a 5 cm-diameter container. Photographs are actual size to facilitate the comparisons with grain samples. The visual scale can be used by passing grain samples over the photographs until the percentage of affected kernels is approximated by the damage seen in the scale. Record the appropriate percentage and continue onto the next sample. It is important to take a random, uniform sample from the harvested wheat. To reduce sampling error and improve mean estimates, multiple readers may be employed, although correlation between evaluators has been high.

Fusarium head blight (head scab), caused by Fusarium graminearum, is an important disease in many wheat growing regions of the United States. Infection causes floret sterility and poor grain fill resulting in reduced yield, test weigh and seed quality. Diseased kernels are often shriveled and may have a white or pink discoloration. Affected grain may also contain mycotoxins that have detrimental affects on animal and human health. Seed that appears unaffected may be contaminated with mycelium or conidia of F. graminearum, resulting in seedling blight and root rot when contaminated seed is planted.

Fusarium head scab – shriveled, moldy seed from diseased head

Damage caused by Fusarium head blight can be quantified by assessing head disease incidence and severity, mycotoxin level in grain, and grain yields. Researchers interested in evaluating fungicide efficacy, or the genetic resistance of wheat cultivars and breeding lines, are also concerned with kernel damage. Estimations of kernel damage are also useful to grain farmers and handlers required to assess grain marketability or feed value.

Acknowledgements:

Ms. Sharon Chapman and Mr. Eric Chanay for assistance in sample preparation.

Mr. Kenneth Chamberlain of the Ohio State University for assistance with photography.

Selected References

Bai, G-H. and Shaner, G. 1994. Scab of wheat: prospects for control. Plant Disease. 78:760-766.

McMullen, M., Jones, R. and Gallenberg, D. 1997. Scab of wheat and barely: a re-emerging disease of devastating impact. Plant Disease. 81:1340-1347.