Submitted to: World Mycotoxin Forum, the Third Conference
Publication Type: Abstract Only
Publication Acceptance Date: 11/6/2006
Publication Date: 12/15/2006
Citation: Brown, R.L. 2006. Pre-Harvest Strategies for Prevention of Mycotoxin Contamination. World Mycotoxin Forum, the Third Conference, Book of Abstracts. p. 65. Interpretive Summary:
Technical Abstract: Aflatoxins are carcinogens produced by Aspergillus flavus and A. parasiticus when these fungi infect crops before and after harvest. Contamination of foods and feeds with aflatoxins, therefore, threatens both human and animal health. Traditional control methods (e.g. cultural practices, pesticides) have not been effective in controlling aflatoxin producing fungi. Our research, therefore, focuses on acquiring knowledge of: 1) the interruption of aflatoxin biosynthesis, 2) fungal populations and biocontrol using atoxigenic A. flavus strains and 3) enhancement of host plant resistance to aflatoxin contamination through a) gene insertion and b) breeding along with the identification of resistance markers in newly-developed lines. Strategies for interrupting aflatoxin biosynthesis could be significantly benefited by previous studies conducted in our lab that identified the cluster of pathway genes, corresponding biosynthetic enzymes and precursor intermediates involved in aflatoxin B1 and B2 synthesis. Our current study of A. flavus genomics provides an innovative strategy and rapid investigative tool for simultaneous analysis of the biochemical function and genetic regulation of fungal genes to understand the molecular regulation of aflatoxin biosynthesis. A project is currently underway to identify, through EST technology, the complex gene array involved in fungal virulence, aflatoxin formation, signaling pathways between the fungus and the environment and fungal reproduction/survival. Microorganisms have often been suggested as agents for control of aflatoxin contamination. The best biocompetitive agent to control A. flavus would be atoxigenic strains of A. flavus, because these strains are expected to be adaptable to environmental conditions identical to the toxigenic strains and would be biologically active. Research demonstrating success in the competitive exclusion of toxigenic strains by atoxigenic strains and subsequent drastic reductions of aflatoxin levels in cottonseed have led to an industry/ARS partnership in support of extensive field trials in Arizona and the large scale development of atoxigenic strains. Recently, this technology and the assessment of its impact has been extended to areas of Texas and California and now include rotation crops, particularly corn. Plant breeding for resistance is practicable for corn due to the existence of a large germplasm pool with differential resistance. However, genetic engineering may be essential for cotton since it contains little resistance to aflatoxin contamination in its seed. Genes encoding antifungal proteins have been identified and cotton has been transformed with these genes and is being tested for enhanced resistance to aflatoxigenic fungi. A rapid and simple laboratory-based kernel screening assay (KSA) was developed that enhances resistance screening for corn breeders and facilitates the study of kernel resistance mechanisms. The strategy of comparing kernel proteomes of resistant with susceptible genotypes has facilitated the discovery of antifungal and stress related proteins associated with resistance (RAPs). This strategy is enhanced by the discovery of closely-related corn lines differing in resistance among lines produced in a West African breeding program combining resistant germplasm from the U.S. with that discovered in Central and West Africa. Confirmation of a role for resistance associated proteins/corresponding genes in resistance would yield markers useful to breeders to develop agronomically superior resistant corn lines.