Clonality and host selection in the wheat pathogenic fungus Puccinia triticina
ABSTRACT Clonal reproduction in Puccinia triticina, the cause of wheat leaf rust, has long been hypothesized but has never been demonstrated. Using a population genetics approach and microsatellite markers, we analysed genetic diversity of this fungus at each level of genome organisation. Sampling included isolates from two field populations growing on two cultivars carrying specific resistance genes, completed with isolates representing the main pathotypes identified from a national survey. For the two cultivars, populations differentiated according to the distribution of their genotypes and pathotypes. There was a high proportion of repeated genotypes, combined with a significant linkage disequilibrium and a strong negative value for FIS. These three factors, especially heterozygote excess, strongly support the hypothesis of a high rate of clonal reproduction. Each pathotype matched a unique multilocus genotype, except for a few isolates, which were taken to be mutants of the dominant genotype. We discussed the strong relationship between pathotypes and genotypes as the consequence of clonal reproduction combined with a strong selection exerted by host cultivars. (c) 2007 Elsevier Inc. All rights reserved.
Article: Phylogeography and population structure of the grape powdery mildew fungus, Erysiphe necator, from diverse Vitis species.[show abstract] [hide abstract]
ABSTRACT: The grape powdery mildew fungus, Erysiphe necator, was introduced into Europe more than 160 years ago and is now distributed everywhere that grapes are grown. To understand the invasion history of this pathogen we investigated the evolutionary relationships between introduced populations of Europe, Australia and the western United States (US) and populations in the eastern US, where E. necator is thought to be native. Additionally, we tested the hypothesis that populations of E. necator in the eastern US are structured based on geography and Vitis host species. We sequenced three nuclear gene regions covering 1803 nucleotides from 146 isolates of E. necator collected from the eastern US, Europe, Australia, and the western US. Phylogeographic analyses show that the two genetic groups in Europe represent two separate introductions and that the genetic groups may be derived from eastern US ancestors. Populations from the western US and Europe share haplotypes, suggesting that the western US population was introduced from Europe. Populations in Australia are derived from European populations. Haplotype richness and nucleotide diversity were significantly greater in the eastern US populations than in the introduced populations. Populations within the eastern US are geographically differentiated; however, no structure was detected with respect to host habitat (i.e., wild or cultivated). Populations from muscadine grapes, V. rotundifolia, are genetically distinct from populations from other Vitis host species, yet no differentiation was detected among populations from other Vitis species. Multilocus sequencing analysis of the grape powdery mildew fungus is consistent with the hypothesis that populations in Europe, Australia and the western US are derived from two separate introductions and their ancestors were likely from native populations in the eastern US. The invasion history of E. necator follows a pattern consistent with plant-mediated dispersal, however, more exhaustive sampling is required to make more precise conclusions as to origin. E. necator shows no genetic structure across Vitis host species, except with respect to V. rotundifolia.BMC Evolutionary Biology 01/2010; 10:268. · 3.52 Impact Factor