Genetic structure of <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> populations isolated from maize in Argentina

Fusarium verticillioides (sexual stage Gibberella moniliformis) is a common fungal pathogen of maize worldwide that also produces fumonisin mycotoxins. Populations of this fungus can be diverse with respect to neutral and selectable genetic markers. We used vegetative compatibility groups (VCGs) and amplified fragment length polymorphisms (AFLPs) to evaluate the genetic structure of three F. verticillioides populations from commercial maize fields in Argentina. Based on work with similar populations from outside South America, we expected individuals within the populations to be genetically diverse, that genotypic variation would be distributed in a manner consistent with random mating, and that populations from different locations would be genetically indistinguishable from one another. We analysed 62 AFLP loci for 133 fungal isolates. All three populations were genotypically diverse but genetically similar and potentially part of a larger, randomly mating population, with significant genetic exchange occurring between the three subpopulations. There was no evidence for linkage disequilibrium at P = 0.05. The low values of G _ST , the lack of frequent private alleles, and the lack of a systemic pattern of linkage disequilibrium all suggest that sexual reproduction is sufficiently common in F. verticillioides and that the dispersal of strains is sufficiently efficient for the population of F. verticillioides in the main maize growing region to be a single randomly mating population with no detectable genetic subdivision. Thus differences in disease and/or toxin production observed in this region are best attributed to differences other than the genetic composition of the population.