Deepak Bhatnagar Kanniah Rajasekaran Jeffrey W Cary Robert Brown Jiujiang Yu and Thomas E Cleveland

Abstract

Aflatoxins are extremely carcinogenic secondary metabolites produced by Aspergillus fla-vus when this fungus invades crops such as maize, cotton, tree nuts and peanuts. Adverse health effects from the ingestion of these toxins have caused regulatory agencies throughout the world to limit the amount of aflatoxins that are permitted in food or feed that is available for sale. This results in undue economic burden on the grower. New biotechnologies such as: (i) the use of disarmed, non-toxigenic biocompetitive strains of A. flavus in biocontrol of aflatoxin contamination, and (ii) identification of plant constituents that disrupt aflatoxin biosynthesis or fungal growth and their use in new biochemical marker-based breeding strategies to enhance resistance in crops to aflatoxin, could potentially save the agricultural industry in the United States alone hundreds of millions of dollars. In addition to the above mentioned studies, USDA, Agricultural Research Service scientists and other researchers have been studying the genetics of the biosynthetic pathway of this important toxin in order to understand how and why this fungus makes aflatoxins. With this knowledge, strategies are being developed to interrupt aflatoxin synthesis, thereby preventing aflatoxin contamination of crops. The fungal genome of A. flavus has been sequenced to understand the regulation of aflatoxin formation by environmental factors. This information is being used to assist in the development of host-resistance against aflatoxin contamination by studying the effects of various physiological parameters, e.g., drought stress on gene expression in toxigenic fungi. The toxin biosynthetic machinery in the fungus also can be disrupted, which may enable the development of atoxigenic fungal strains that can be used as "designer" biocontrol agents.

Introduction

Aflatoxins are natural poisons produced predominantly by two common fungi, Aspergillus flavus and Aspergillus parasiticus. A. flavus is most commonly found in agricultural fields, and when it invades crops like maize, peanuts, cotton, and tree nuts, it produces aflatoxins if the environmental conditions permit. Chronic, as well as sporadic, aflatoxin contamination in a variety of field crops and agricultural commodities worldwide has had a serious impact

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