Ear Spray Targeting for Improved Ear Blight and Mycotoxin Control

Since cultural measures, fungicides, and resistant cereal genotypes have provided only partial control of Fusarium head blight to date, biological control is being explored as an additional tool in the integrated management of this disease. Microbial antagonists or their metabolites are potentially useful in the disruption of spike infection, fungal spread within the spike, seedling blight development, saprophytic survival of the fungus in crop residues, and fungal sporulation on crop residues. Initial efforts have been focused on bioprospecting for microbial antagonists of Gibberella zeae. Bioprotectants have been selected primarily based on their antibiosis and competition abilities, though mycoparasitism, induced resistance, and metabolic inhibition of mycotoxin synthesis are also useful mechanisms of biological control. Numerous isolates of yeast, spore-forming bacteria, and other bacteria have been identified that reduced FHB and/or mycotoxin contamination in laboratory, greenhouse, or small-scale field tests, sometimes with a magnitude of control equivalent to fungicide applications. But a lack of consistency in FHB control, especially in variable field environments, has hampered the transition from the laboratory to meaningful field-testing of biological control agents. Almost nothing is known about the ecology, survival, and antimicrobial activity of biological control agents following their application to plant surfaces in field environments – a fundamental knowledge gap. Some research is underway and much more is needed to define controlled culture systems for producing biological control products of consistently high quality that could then be tested in uniform regional field tests against FHB. Product formulation and application technologies are as or more critical to biocontrol efficacy as they are to fungicide efficacy, yet little research has been conducted in the context of biological control agents. Bioprotectants, especially isolates of spore-forming bacteria, may be combined with foliar fungicides to further reduce FHB mycotoxin contamination in cereal cultivars with partial resistance to FHB. Antifungal metabolites of biological control agents should also be considered as direct tools in the integrated management of FHB. These substances might be applied as foliar sprays or the genes encoding their synthesis might be genetically engineered into cereal crops along with appropriate tissue-specific promoters. While there are significant challenges to overcome, biological control strategies hold considerable promise for contributing to the long-term management of FHB.