Evolution of azole resistance and thermal adaptation in global populations of Parastagonospora nodorum

Danilo Augusto dos Santos Pereira 1 Daniel Croll 2 Bruce A. McDonald 1 Patrick C. Brunner 1
1Institute of Integrative Biology, Plant Pathology Group, Swiss Federal Institute of Technology, Zurich, Switzerland
2Institute of Biology, Laboratory of Evolutionary Genetics, University of Neuch√Ętel, Neuch√Ętel, Switzerland

Organisms become adapted to their local environment through natural selection. This process is easily observed in agroecosystems where human activities result in rapid evolution of fungal plant pathogens towards higher levels of virulence and reduced sensitivity to fungicides. Different pathogen populations may respond differently to the same human-imposed selection. A sustainable management of crop diseases requires improved knowledge of the genetic basis of the observed phenotypes in pathogen populations. A first step to obtain this knowledge is to differentiate the evolutionary forces acting on quantitative traits by using a QST /FST comparison. QST describes the distribution of the phenotypic variation in quantitative traits within and among populations while FST describes the distribution of neutral genetic variation within and among populations. The joint comparison of QST and FST indexes enables evaluation of the causes of adaptive divergence in quantitative traits that reflect local adaptation of the organism. Parastagonospora nodorum is a globally distributed necrotrophic pathogen causing the Stagonospora nodorum leaf and glume blotch (SNB) disease on wheat. We conducted a QST /FST analysis using 176 isolates sampled from field populations in Switzerland, South Africa, Australia, China, Oregon, New York, Texas and Iran. QST values were obtained by phenotyping all isolates for azole sensitivity (EC50) and thermal adaptation (growth rate at different temperatures). Full genome sequences of all isolates were used to calculate FST based on neutral single nucleotide polymorphisms (SNPs). We also conducted a genome-wide association study (GWAS) for the same isolates to identify genomic regions and candidate genes associated with the observed variation for fungicide sensitivity and thermal adaptation.