|Bowden, Robert - Bob|
Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2003
Publication Date: 3/15/2004
Citation: Zeller, K.A., Bowden, R.L., Leslie, J.F. 2004. Population differentiation and recombination in wheat scab populations of gibberella zeae in the united states. Molecular Ecology. 13:563-571. Interpretive Summary: Fusarium head blight, or scab, is an important disease affecting yield and quality of wheat and barley. The main cause of the disease in North America is the fungus Fusarium graminearum, also known as Gibberella zeae. Our objective in this study was to test the hypothesis that G. zeae consists of a uniform population throughout the central and eastern United States across a span of several years. We analyzed molecular markers of G. zeae from more than 500 isolates in eight field populations from seven states collected during the 1998, 1999 and 2000 cropping seasons. We found that all of the populations have high genotypic diversity and appeared to be interbreeding. All populations had high similarity to each other. There was some evidence that populations farther apart differed slightly. The results of this study found no evidence for differences in subpopulations that might affect breeding for disease resistance.
Technical Abstract: In limited previous studies of the Ascomycete fungus G. zeae in North America, the populations examined were genetically and phenotypically diverse and apparently constitute subsamples from a larger population. Our objective in this study was to test the hypothesis that a homogeneous, randomly mating population of G. zeae is contiguous throughout the central and eastern United States across a span of several years. We analyzed presence/absence alleles based on Amplified Fragment Length Polymorphisms (AFLPs) at 30 loci, 24 of which are genetically defined on a linkage map of G. zeae, from > 500 isolates in eight field populations from seven states collected during the 1998, 1999 and 2000 cropping seasons. All of these strains had AFLP profiles similar to those of standard isolates of G. zeae phylogenetic lineage 7. All of the populations have high genotypic diversity, little or no detectable genetic disequilibrium, and show evidence of extensive inter-population genetic exchange. Allelic frequencies from some of the populations examined are not statistically different from one another, but others are. Thus, the populations examined are not mere subsamples from a single, large, randomly mating population. Geographic distance and genetic distance between populations are significantly correlated. The observed differences are relatively small, however, indicating that while genetic isolation by distance may occur, genetic exchange has occurred at a relatively high frequency among U.S. populations of G. zeae. We think that these differences reflect the time required for the alleles to diffuse across the distances that separate them, since relatively little linkage disequilibrium is detected either in the population as a whole or in any of the individual subpopulations.