Ecology of Aspergillus avus, regulation of aatoxin production, and management strategies to reduce aatoxin contamination of corn

The contamination of corn (maize) by fungi and the accumulation of mycotoxins are a serious agricultural problem for human and animal health. One particular devastating group of mycotoxins, called aatoxins, has been intensely studied since the 1960s. Studies of Aspergillus avus, the agriculturally relevant pro- ducer of aatoxins, have led to a well-characterized biosynthetic pathway for aatoxin production, as well as a basic understanding of the organism’s life cycle. Unfortunately, these eorts have not resulted in corn production practices that substantially reduce aatoxin contamination. Similarly, the use of agrochemicals (e.g., fungicides) results in very limited reduction of the fungus or the toxin. Thus, cultural management (fertility and irrigation) coupled with aggressive insect management is current recommendation for inte- grated aatoxin management. The development of resistant hybrids appears to be a very promising tech- nology, but commercial hybrids are still not available. Thus, biocontrol appears to be the most promising available avenue of reducing aatoxin accumulation. Biocontrol utilizes nontoxigenic strains of Aspergillus to reduce the incidence of toxin-producing isolates through competitive displacement. To maximize the eectiveness of biocontrol, a thorough knowledge of the environmental factors inuencing colonization and growth of Aspergillus is needed. A. avus not only colonizes living plant tissue, but it also grows sapro- phytically on plant tissue in the soil. These residues serve as a reservoir for the fungus, allowing it to over- winter, and under favorable conditions it will resume growth and release new conidia. The conidia can be transmitted by air or insects to serve as new inoculum on host plants or debris in the eld. This complex ecology of Aspergilli has been studied, but our understanding lags behind what is known about biosynthe- sis of the toxin itself. Our limited understanding of Aspergilli soil ecology is in part due to limitations in eval- uating Aspergilli, aatoxin, and the biosynthetic genes in the varying aspects of the environment. Current methods for assessing Aspergillus and aatoxin accumulation rely heavily on cultural and analytical meth- ods that are low throughput and technically challenging. Thus to understand Aspergillus ecology and envi- ronmental eects in contamination to maximize biocontrol eorts, it is necessary to understand current treatment eects and to develop methodologies capable of assessing the fungal populations present. In this manuscript we discuss the current knowledge of A. avus ecology, the application of selected molecu- lar techniques to eld assessments, and crop practices used to reduce aatoxin contamination, focusing on chemical treatments (fungicides and herbicides), insect management, and crop management.