|Kolmer, James - Jim|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2009
Publication Date: 5/20/2009
Citation: Kolmer, J.A., Ordonez, M.E. 2009. Differentiation of Molecular Genotypes and Virulence Phenotypes of Puccinia triticina from Common Wheat in North America. Phytopathology. 99:750-758.
Interpretive Summary: Leaf rust is an important disease of wheat caused by a fungus called Puccinia triticina. This disease occurs throughout most of the wheat growing regions of the U.S. The population of the leaf rust fungus in the U.S. was studied using different types of genetic markers to determine how many distinct groups of the fungus are present in the U.S. Five genetically distinct groups were described. These five groups are found in all regions of the wheat growing regions. The groups differ in their ability to attack leaf rust resistance genes in wheat. This information can possibly be used to develop a strategy for resistance genes in wheat. The results also indicated that new groups of Puccinia triticina have not been introduced to the U.S. from other countries or continents since the mid 1990s.
Technical Abstract: Wheat leaf rust caused by Puccinia triticina is widely distributed in the wheat growing regions of the U.S. and Canada, and is subject to selection for virulence phenotype by leaf rust resistance genes in wheat cultivars. The objective of this study was to determine the number of genetically differentiated groups of P. triticina that are present in North America. A total of 148 isolates of P. triticina from the 1980s-2005 were collected from wheat growing regions of the U.S. and Canada and tested for virulence on 20 lines of wheat with single genes for leaf rust resistance and for molecular genotype with 23 simple sequence repeat (SSR) markers. A total of 91 virulence phenotypes and 65 SSR genotypes were found. After removal of isolates with identical virulence and SSR genotypes, 125 isolates were included for further analysis. Bayesian cluster analysis indicated five different groups of isolates based on SSR genotypes that also differed for virulence to leaf rust resistance genes Lr2a, Lr2c, Lr3bg, Lr17, and Lr28. Isolates avirulent to Lr14a and Lr20 that have increased since 2003 had identical or similar SSR genotypes as older isolates in one of the five groups, indicating that these isolates were derived by mutation from the previously existing population of P. triticina. The representative collection of P. triticina isolates had characteristics consistent with an asexual dikaryotic population of genetically differentiated groups of SSR genotypes with high levels of heterozygosity and disequilbrium within which step-wise mutation at avirulence/virulence loci regularly occurs.