Stephen Harrison, Arceneaux, Kelly J., Price, III, Paul P, Padgett, Guy B.
Stephen Harrison, Kelly Arceneaux, Niranjan Baisakh, Boyd Padgett and Paul P. “Trey” Price III
Fusarium head blight has become the major limiting factor of high yield and quality wheat in the Gulf Coast region in the past decade. The disease is caused by a fungal pathogen that infects wheat heads during flowering, causing shriveled and discolored grain or unfilled florets. It is also referred to as scab because of the discolored areas of heads infected by the disease. Fusarium head blight has significantly contributed to the decline in wheat acreage in Louisiana over the past 10 years. Wheat acreage now hovers around 20,000 acreas compared with more than 200,000 acres 10 years ago.
A crop heavily infected by Fusarium head blight will have reduced yield, low test weight and mycotoxin levels above the permitted level, resulting in rejection by grain elevators. Currently, there are only a few varieties with a significant level of resistance to the disease adapted to the Gulf Coast.
Louisiana wheat enters export markets through Mississippi River elevators, so it is important that locally adapted, scab-resistant varieties be identified and developed. The best way to control wheat scab is the application of effective fungicides at flowering, coupled with use of a variety containing several resistance genes. The wheat breeding program devotes a large amount of resources to develop resistance and uses inoculated, misted nurseries and molecular marker technology.
Of the 461 wheat crosses made in 2020, 89% included parents with high Fusarium head blight resistance and/or known resistance genes. The parents were chosen to combine good yield and agronomic characteristics with resistance genes from both parents in each cross. Molecular markers play a key role in this aspect of the breeding program. There are about two dozen known genes that confer some level of disease resistance, but none that do so adequately alone. The only way to know what genes each parent has, and to combine several different genes into one breeding line, is to run molecular markers for the different Fusarium head blight genes on candidate parents and advanced lines. Genomic selection is also an important aspect because it allows estimation of the cumulative effect of many minor genes for resistance present in the best breeding lines.
Wheat varieties susceptible to Fusarium head blight are grown both in misted test areas and in normal field settings to test commercial and experimental fungicides for efficacy. Fungicides are applied during flowering, which is the optimum timing for scab, at labeled rates and appropriate water volumes. Plots are then visually rated for Fusarium head blight multiple times during the rest of the season. At maturity, plots are harvested using a specialized combine. Currently, recommended commercial fungicides for scab management include: Caramba, Miravis Ace, Proline and Prosaro. Unfortunately, we can only achieve 50% control with the best fungicides and highest water volumes; therefore, planting scab-resistant varieties remains of utmost importance.
The wheat breeding program has made tremendous strides in development of Fusarium head blight resistant varieties over the past decade. Today’s varieties are much more resistant than varieties from 20 years ago and continue to improve. Likewise, tremendous strides have been made in development and deployment of fungicides for Fusarium head blight management.
Stephen Harrison is a professor, Kelly Arceneaux is a research associate, Niranjan Baisakh is an associate professor, all in the School of Plant, Environmental and Soil Sciences. Boyd Padgett is a professor, and Paul P. “Trey” Price III is an associate professor, both in the Central Region.
(This article appears in the spring 2021 issue of Louisiana Agriculture.)
Wheat and oat breeder Stephen Harrison observes fields of grain varieties at an AgCenter field day. Photo by Bruce Schultz