|Bock, C. H. - USDA, ARS|
|Thrall, P. H. - CSIRO (AUSTRALIA)|
|Burdon, J. J. - CSIRO (AUSTRALIA)|
Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 5, 2004
Publication Date: February 1, 2005
Citation: Bock, C., Thrall, P., Burdon, J. 2005. Substantial genetic variation in populations of alternaria brassicicola suggests the occurrence of sexual recombination. Mycological Research. 109:227-236. Technical Abstract: Substantial polymorphism was detected between isolates from five populations of Alternaria brassicicola attacking Cakile maritima along the New South Wales coast of Australia, with a maximum of two genotypes being shared between population pairs. Of ten pair-wise population comparisons, six had no pathogen genotypes in common; only one genotype occurred five times, and most (93%) were found only once. Although an UPGMA based on Nei's measure of genetic distance clearly separated the five populations, a cluster analysis using individual isolates failed to group them according to population, indicating significant gene flow. An analysis of molecular variance indicated ca. 14% of the variation occurred between populations, suggesting only limited population differentiation. Tests of the relative contribution of clonality and sexual recombination indicated low, albeit significant levels of linkage disequilibrium in all populations. The observed level of linkage disequilibrium, and the high genotype diversity provides support for the contention that a hitherto unidentified sexual stage might be a significant factor in the lifecycle of A. brassicicola.