Introduction

Mycotoxins are fungal metabolites that can contaminate foods and feeds, and exhibit toxic effects in higher organisms (Sharma and Salunkhe 1991) that consume the contaminated commodities. The regulatory guidelines and advisory limits issued by the United States Food and Drug Adminstration (FDA) on some contaminated commodities can facilitate severe economic losses to the growers. Therefore, mycotoxin contamination of foods and feeds is a serious food safety problem affecting the competitiveness of U.S. agriculture, both domestically and worldwide. Mycotoxins that significantly impact agriculture include aflatoxins produced by Aspergillus flavus and A. parasiticus, trichothecenes (in particular deoxynivalenol or DON) produced by Fusarium spp., ochratoxins produced by A. ochraceus and Penicillium viridicatum, and fumonisins produced by F. verticillioides (synonym, moniliforme, as used in some literature cited in the present article) (Brown et al. 1998). Cyclopiazonic acid produced by A. flavus, can also be included on this list of significant mycotoxins. Aflatoxins, potent liver toxins, and carcinogens comprise the most widely studied mycotoxins (CAST 1979; Diener et al. 1987; Payne 1998), because of established results in their ability to induce animal diseases, particularly liver cancer in humans [reviewed in Eaton and Groopman (1994)]. However, other mycotoxins such as DON, are of particular concern for the brewing industry which has cutoff levels as low as 0.5 ppm for DON in barley used in malting (Robens 2001). In addition, recognizing the potential for fumonisins to cause animal or human health problems (Marasas 1996), the FDA has now announced the availability of a final guidance document entitled "Guidance for Industry: Fumonisin Levels in Human Foods and Animal Feeds" in the November 9, 2001, Federal Registry. More than 50 countries have established or proposed regulations for controlling aflatoxins in foods and feeds, and at least 15 countries have regulations for levels of other mycotoxins (Haumann 1995). The FDA has set limits of 20ppb, total aflatoxins, for interstate commerce of food and feed and 0.05 ppb of aflatoxin M1 for sale of milk. Because of both food and feed safety concerns and the establishment of regulatory limits on DON and aflatoxins, it is estimated that over $1.5 billion in crop losses occur annually due to contamination of corn, cottonseed, peanut, and treenuts with aflatoxins and of wheat and barley with DON (Robens 2001).

An association between mycotoxin contamination and inadequate post harvest storage conditions has long been recognized. However, studies have revealed that seeds are contaminated with mycotoxins primarily at the preharvest stage [reviewed in Lisker and Lillehoj (1991)]. Therefore, many current research strategies focus on preharvest control of mycotoxins [reviewed in Brown et al. (1998)]. Maintaining good cultural and management practices that promote the general health of crops can reduce but not eliminate preharvest mycotoxin contamination. For example, insect resistant germplasm, such as corn transformed with the gene encoding Bacillus thuringiensis crystal protein (Bt maize), reduced levels of fumonisins (Dowd 2000). Irrigation of peanut essentially prevents aflatoxin contamination of this crop, probably by preventing drought stress, known to induce contamination in peanut (Cole et al. 1985). However, optimization of management practices to control mycotoxins is not always possible due to production costs, geographic location, or the nature of the production system for the particular crop vulnerable to mycotoxins. In addition, even the best management practices are sometimes negated by biotic and abiotic factors that are hard to control and by extremes in environmental conditions. The complex epidemiology of A. flavus on corn (Wicklow 1991) can drastically affect the outcome of measures to control aflatoxin contamination on this crop. Therefore, there is an urgent need for development and utilization of strategies involving state-of-the-art technologies to control preharvest mycotoxin contamination. The current article highlights recently published and high-impact research involving molecular-based technologies that has been accomplished and that enhances a host plant resistance strategy for controlling mycotoxin contamination.

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