Horn Association between vegetative compatibility and afl atoxin production by Aspergillus species during intraspecifi c competition

Intraspecifi c competition is the basis for biological control of afl atoxins, but there is little understanding of the mechanism(s) by which competing strains inhibit toxin production. Evidence is presented that demonstrates a relationship between strength of the vegetative compatibility reaction and afl atoxin production in Aspergillus fl avus and A. parasiticus using the suspended disk culture method. Combining wild-type afl atoxin-producing isolates belonging to different vegetative compatibility groups (VCGs) resulted in a substantial reduction in afl atoxin yield. Pairs of afl atoxin-producing isolates within the same VCG, but showing weak compatibility reactions using complementary nitrate-nonutilizing mutants, also were associated with reduced levels of afl atoxin B1. In contrast, pairings of isolates displaying a strong compatibility reaction typically produced high levels of afl atoxins. These results suggest that interactions between vegetatively compatible wild-type isolates of A. fl avus and A. parasiticus are cooperative and result in more afl atoxin 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 afl atoxin biosynthesis. By comparison, vegetative incompatibility reactions might result in the death of those heterokaryotic cells composed of incompatible nuclei and thereby disrupt the formation of mycelial networks at the expense of afl atoxin biosynthesis.