Molecular genotype analysis of natural toxigenic and nontoxigenic isolatesof Aspergillus flavus and A-parasiticus

Aspergillus flavus and A. parasiticus are closely related species belonging to the Aspergillus section Flavi. Both species can produce aflatoxins, but not all isolates of either species do so. We examined the genetic relation ship between toxigenic and non-toxigenic isolates using RAPD and Neighbour Joining analysis. Twenty-four RAPD amplifications using a combination of 17 primers discriminated between 20 isolates of A. flavus and 15 isolates of A. parasiticus. A. flavus isolates divided into two distinct groups with bo th toxigenic and non-toxigenic isolates occurring in each group. No associa tion was seen between RAPD genotype and the ability to produce toxin. Five non-toxigenic isolates of A. parasiticus separated into two groups, in whic h the isolates were similar but not identical. These groups of non-toxigeni c isolates occurred on branches in which toxigenic isolates also occurred. This study suggests that either multiple losses of toxigenicity in A. flavu s and A. parasiticus have occurred, or that recombination has reasserted th is phenotype into a variety of different genetic backgrounds.