PMN Proeedings: 2011 Field Crops Rust Symposium

2011 Field Crops Rust Symposium:
Abstract

Tools and Approaches for Characterizing Rust Populations

Presenting Author: J. KOLMER

Affiliation: USDA-ARS Cereal Disease Laboratory, St. Paul, MN, USA

Variation in rust populations was initially assessed by host differential sets that varied for resistance. Collections of cultivars/varieties or cultivars and near-isogenic lines with known single resistance genes were assessed for infection type to characterize virulence and race diversity. Differentials with single resistance genes allow the direct determination of frequency of virulence in rust populations to the corresponding genes. Races of rust and virulence frequencies can be tracked over time on a geographical basis to determine the effect of host resistance genes on virulence in rust populations. Molecular markers, such as AFLPs, SSRs, and SNPs, can be used to assess genetic variation that is not under direct selection by host resistance genes. AFLPs are dominant markers that can detect high levels of polymorphism and can be used directly without sequence knowledge. SSRs are codominant multiallelic markers that require sequence knowledge to design primer pairs that generate polymorphic alleles. SNPs are biallelic, can be adapted to high-throughput genotyping, and are less vulnerable to homoplasy compared to SSR markers. Many populations of cereal rust fungi are asexual and the clonal reproduction of urediniospores maintains associations between virulence and molecular polymorphism. Sexual populations would be expected to show less relationship between molecular markers and virulence. Asexual populations are not in Hardy-Weinberg equilibrium and have higher levels of observed allelic heterozygosity compared to sexual populations. Introductions of new rust genotypes from different geographical regions would be expected to differ for molecular genotype and virulence compared to previously established populations.