Submitted to: Mycoscience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2007
Publication Date: 11/27/2007
Citation: Wicklow, D.T., Horn, B.W. 2007. Association between vegetative compatibility and aflatoxin production by Aspergillus species during intraspecific competition. Mycoscience. 48:267-273. Interpretive Summary: A promising strategy for eliminating preharvest aflatoxin of susceptible crops, especially in environments conducive to an aflatoxin outbreak, involves field applications of non-aflatoxin producing strains of A. flavus and/or A. parasiticus, which displace the naturally occurring aflatoxin-producing strains through mechanisms of intraspecific competition. There is a need to explain the underlying mechanism(s) of competition and this study describes a novel procedure for evaluating Aspergillus interference with aflatoxin production. Evidence is presented which demonstrates a relationship between aflatoxin yield among paired cultures of Aspergillus flavus or A. parasiticus, using the suspended disc culture method, and the extent to which both isolates are capable of producing a cooperative mycelial network.
Technical Abstract: Intraspecific competition is the basis for biological control of aflatoxins, but there is little understanding of the mechanism(s) by which competing strains inhibit toxin production. Evidence is presented which demonstrates a relationship between strength of the vegetative compatibility reaction and aflatoxin production in A. flavus and A. parasiticus using the suspended disc culture method. Combining aflatoxin-producing isolates belonging to different vegetative compatibility groups (VCGs) resulted in a substantial reduction in aflatoxin yield. Pairs of aflatoxin-producing isolates within the same VCG, but showing weak compatibility reactions using complementary nitrate-nonutilizing mutants, also were associated with reduced levels of aflatoxin B1. In contrast, pairings of isolates displaying a strong compatibility reaction typically produced high levels of aflatoxins. These results suggest that interactions between vegetatively compatible wild-type isolates of A. flavus or A. parasiticus are cooperative and result in more aflatoxin B1 than pairings between isolates that are incompatible. Successful hyphal fusions among spore germlings produce a common mycelial network with a larger resource base to support aflatoxin biosynthesis. By comparison, vegetative incompatibility reactions result in the death of those heterokaryotic cells composed of incompatible nuclei and may disrupt the formation of mycelial networks at the expense of aflatoxin biosynthesis.