Submitted to: Mycologia
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2002
Publication Date: 10/10/2002
Citation: Horn, B.W., Dorner, J.W. 2002. Effect of Competition and adverse culture conditions on aflatoxin production by aspergillus flavus through successive generations. 94(5):741-751. Interpretive Summary: Aspergillus flavus is a fungus that infects seeds of peanuts, cotton, corn and tree nuts and contaminates them with aflatoxins, carcinogenic compounds that pose a significant health hazard to animals, including humans. Although A. flavus is easily grown in the laboratory, it often quickly loses its ability to produce aflatoxins. In nature, however, such degeneration does not occur. The purpose of this study was to identify the environmental factors responsible for maintaining aflatoxin- producing ability in nature. The experiments suggest that adverse environmental conditions (high temperature, low pH and nutrient deprivation) but not competition with other microorganisms allow the fungus to produce aflatoxins from one generation to the next. Knowledge of the environmental factors that are responsible for maintaining aflatoxin production in nature is necessary for devising strategies to control these fungi in agricultural fields.
Technical Abstract: Strains of Aspergillus flavus often degenerate with serial transfers on culture media, resulting in morphological changes and loss of aflatoxin production. However, degeneration does not readily occur in nature as indicated by the wild-type morphological characters of newly isolated strains and the high percentage of aflatoxigenic A. flavus from soil and crops in some geographic regions. In this study, three aflatoxin-producing strains of A. flavus were serially transferred using conidia for 20 generations (three independent generation lines per strain) on potato dextrose agar at 30 C. The rate of degeneration was compared to that of cultures grown in the presence of competing fungi (A. terreus, Penicillium funiculosum and the yeast, Pichia guilliermondii) and under adverse conditions of elevated temperature, reduced water activity, low pH and nutrient deprivation. Formation of morphological variants and the associated loss of aflatoxin production over generations varied considerably according to strain and the generation line within each strain. In the strain most sensitive to degeneration on potato dextrose agar, aflatoxin-producing ability was maintained to varying degrees under adverse conditions but not when A. flavus was competing with other fungi.