VEGETATIVE COMPATIBILITY WITHIN POPULATIONS OF ASPERGILLUS-FLAVUS, ASPERGILLUS-PARASITICUS, AND A-TAMARII FROM A PEANUT FIELD

The diversity of vegetative compatibility groups in Aspergillus flavus, A. parasiticus and A. tamarii, mycotoxigenic fungi that produce aflatoxins and/or cyclopiazonic acid in peanut seeds, was examined. Soil samples were collected from a peanut field shortly after planting and peanut seeds were later harvested from the same soil sites. Aspergillus tamarii isolates were divided into morphologically distinct types A and B. A chlorate medium was used to select for nitrate-nonutilizing mutants (niaD, nirA, and cnx). Vegetative compatibility groups were determined by pairing complementary mutants on a nitrate medium. Diversity of vegetative compatibility groups, expressed as the number of groups divided by the total number of isolates, was in order of increasing diversity: A. tamarii type A (0.15); A. parasiticus (0.22); A. tamarii type B (0.31); and A. flavus (0.56). All isolates were incompatible in interspecific pairings; isolates of A. tamarii type A were also incompatible with type B isolates. Populations of A. parasiticus and A. tamarii types A and B in the peanut field showed a nonrandom distribution of soil isolates based on their vegetative compatibility groups, suggesting that isolates of a group represented, to some degree, a single clone. The high diversity of vegetative compatibility groups in A. flavus may be due to the influx of genetic variability through aerial spore dispersal from infected corn and cotton.