Fusarium Ear Blight - Control Measures

Control Measures

(A) Resistant cultivars Since 1990, an extensive research endeavor has focused on development and use of resistant cereal cultivars and integrated pest management systems for the control of Fusarium head blight. Thousands of plant lines are subjected to artificial inoculation with F. graminearum. Those lines having reduced fungal growth and low levels of seed contamination with the mycotoxin DON are selected and advanced in additional breeding trials.

To date, sources of resistance conferring complete resistance to FHB have not been identified in wheat. Quantitative Trait Loci (QTL) composed of one or more genes, such as Fhb1 derived from the Chinese wheat cultivar Sumai 3, have been identified in wheat. However, these genes confer only partial resistance to FHB, and many of the initial sources of resistance were not well adapted to most of the grain production regions of the U.S. While some success has been made in transferring FHB resistance from such exotic sources into adapted cultivars, identification and deployment of FHB resistance already present in local native germplasm and cultivars is providing another means to achieve this goal. Ultimately, control of FHB, to meet the very low DON limits in wheat grain, will require an integrated approach including development of cultivars having multiple resistance genes and use of fungicides.

Fusarium head blight resistance is a complex trait,. Two to five major genes, plus several minor genes, have been reported from various sources of FHB resistance . QTLs for FHB resistance have been mapped to almost all wheat chromosomes when different mapping populations were investigated. In Sumai 3, QTLs for FHB resistance have been identified on 3BS, 5AS, 6AS, 6BS, and 3BSc, a QTL region proximal to the centromere on 3BS,. In Wuhan 1, the QTLs for FHB resistance were mapped to 2DL and 4B, QTLs on other chromosomes were also reported including those on chromosomes 2A, 2B, 3A, 3B, 5D, 6D, 5B, 4A, 1B, and 7A in wheat germplasm from Europe, Brazil, and Asia. But only the QTL on 3BS from the Chinese cultivar Sumai 3 consistently showed a major effect on Type II resistance across different genetic backgrounds and environments. Other QTLs for FHB resistance exhibited a minor effect, and their expression varied significantly with genetic backgrounds and the environments where the disease was evaluated. Therefore, Sumai 3 has been extensively used as a major source of resistance to FHB in breeding programs worldwide. However, heavy use of narrow FHB resistance sources may increase selection pressure on the pathogens to wear away the effectiveness of the resistance genes involved. New FHB resistance germplasm are desired to broaden the genetic diversity of FHB resistant sources and improve the level of wheat resistance to FHB.

(B) Agronomic management practices Crop sequence (what crops were planted and when) and tillage (soil incorporation of crop residues) have been shown to affect the incidence of FHB. In recent years, decreases in tillage are thought to have contributed to regional scab epidemics by increasing levels of inoculum available for infection. Since the risk of FHB depends on a viable inoculum source, the management of cereal debris on the soil surface may or may not impact the level of FHB. The relative contribution of inoculum from local and distant sources is not yet fully understood. In regions where there is a significant source of airborne inoculum, local management of the disease (on a single farm) may not be effective

(B) Chemical control Chemical controls, such as fungicides, provide partial control of FHB and associated mycotoxin contamination. A number of foliar fungicides have been used to manage FHB in some areas and are applied around the period of wheat flowering. In many areas, fungicides are rarely used for FHB control because of high cost, variable efficacy, and the erratic nature of FHB epidemics. Research continues to identify fungicides that are more effective for the control of FHB.

(c) Biological control Several investigators are focused on finding affordable and environmentally compatible biocontrol agents for the management of FHB. Biocontrol agents could play an important role in organic cereal production. In conventional production, such agents may extend protection of spikes past the flowering stage after fungicides can no longer be applied. Certain strains of spore- producing bacteria (such as Bacillus species) and yeasts (such as Cryptococcus flavescens) show some promise for the control of FHB and the reduction of mycotoxin contamination, however there effectiveness at field level is not well known.

(d) Integrated management Integrated management of FHB may one day be achieved by the combined application of biocontrol agents and fungicides to flowering wheat and barley varieties with partial resistance. Disease forecasting models may help to optimize FHB management by targeting fungicide and biocontrol applications.The online Fusarium Head Blight Risk Assessment Tool (http://www.wheatscab.psu.edu/riskTool_2010.html) may be used to gauge the relative risk of FHB in wheat fields in the U.S. A public outreach program called Scab Smart provides U.S. wheat and barley growers with the latest information on integrated management tools that can be applied in their section of the country. Disease Forecasting models help producers determine the risk of FHB infection at the flowering period of wheat, and thus help optimize FHB management by having fungicides applied only when models indicate that the risk of FHB infection is present, based on current weather parameters. The spring wheat model also has the option for the producer to choose the level of resistance present in the wheat variety grown. Level of resistance affects the FHB risk.

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