Vegetative compatibility within populations of Aspergillus flavus, A. parasiticus, and A. tamarii from a peanut field

Abstract

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.

Key Words:

• Aspergillus flavus
• Aspergillus parasiticus
• Aspergillus tamarii
• peanut
• population
• soil
• vegetative compatibility