Development of Aspergillus Flavus Af36

Aflatoxins are highly toxic cancer causing fungal metabolites known to cause immune-system suppression, growth retardation, liver disease, and death in both humans and domestic animals. Human exposure to aflatoxins is limited by regulations that prohibit the use of crops containing excess quantities of aflatoxins for foods and feeds. Aflatoxins are regulated in part per billion (ppb) ranges with the maximum allowable level varying with country and intended use of the commodity. The quantity permitted in U.S. foods ranges from 0.5 ppb to 20 ppb. Aspergillus flavus, the asexual species responsible for most aflatoxin contamination of many crops, is composed of many genetic groups, called vegetative compatibility groups, that vary widely in several characteristics. Aspergillus flavus is not sufficiently aggressive as a pathogen to cause meaningful losses in yield. However, infection of crop components predisposed by stress, insect damage or the environment can result in high aflatoxin levels. Relatively small proportions of a crop infected with highly toxic isolates can result in unacceptable crop aflatoxin content. Isolates of A. flavus belonging to different vegetative compatibility groups may produce widely different quantities of aflatoxins and fungal communities resident in different areas frequently vary in average aflatoxin-producing potential. Some naturally occurring isolates of A. flavus produce no aflatoxins and are called atoxigenic strains. Certain atoxigenic strains have the ability to competitively exclude aflatoxin-producing strains during crop infection and thereby reduce aflatoxin contamination. One of these, AF36, has been registered as a biological control for the competitive exclusion of aflatoxin producing fungi from cottonseed. The registration process for AF36 that began in 1993 and extended over a decade succeeded in facilitating treatment of over 100,000 acres (Figure 1). The process was greatly facilitated by the IR-4 which served as a liaison and helped prepare and file submissions to EPA.