ARS | Publication request: Lack of Genetic Differentiation Between Puccinia triticina Collections from North and South America

Submitted to: Phytopathology
Publication Type: Abstract
Publication Acceptance Date: March 15, 2008
Publication Date: May 15, 2008
Citation: Ordonez, M.E., Kolmer, J.A. 2008. Lack of Genetic Differentiation Between Puccinia triticina Collections from North and South America [abstract]. Phytopathology. 98:5117.

Interpretive Summary: Leaf rust, caused by the fungus Puccinia triticina is the most common disease of wheat in the United States and also in South America. There are many different biologic forms of the leaf rust fungus, which differ in ability to attack wheat plants with different leaf rust resistance genes. The objective of this study was to compare the biologic forms of the leaf rust fungus from North America with collections from South America using DNA based molecular markers. The results of this study indicated that biologic forms of leaf rust that are found in both North and South America had very similar or identical DNA markers. This indicated that migration of the leaf rust fungus most likely occurs between the two continental regions, or that the same biologic forms were introduced when wheat cultivation began in both regions. The results indicate that new races of leaf rust may quickly spread from one continent to another, possibly endangering wheat cultivars in both continents.

Technical Abstract: Isolates (265) of Puccinia triticina from Argentina, Brazil, Chile, Peru,Uruguay, Canada and the US were tested for polymorphism at 23 simple sequence repeat (SSR) loci, and tested for virulence on 20 Thatcher near-isogenic lines of wheat. Grouping of the isolates through a Bayesian model-based clustering method with SSR allele frequencies separated the populations of North and South America into 10 groups. However, major groups of isolates with similar virulence phenotypes from both continents were not significantly differentiated based on SSR genotypes. Introduction of similar genotypes into both North and South America and/or migration of P. triticina between the two continents has likely occurred. Isolates between the two continents differ for virulence since the populations undergo mutation and are selected for virulence to the Lr resistance genes. in the different wheat cultivars of each region. P. triticina populations in both continents had high levels of SSR heterozygosity and disequilibria typical of asexual populations.