|German, S -|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2010
Publication Date: April 15, 2010
Repository URL: http://hdl.handle.net/10113/42142
Citation: Ordonez, M.E., German, S.E., Kolmer, J.A. 2010. Genetic Differentiation within the Puccinia triticina Population in South America and Comparison with the North American Population Suggests Common Ancestry and Intercontinental Migration. Phytopathology. 100:376-383. Interpretive Summary: Leaf rust caused by the fungus Puccinia triticina is a major disease of wheat in South America and North America. This study was conducted in ordet to determine if genetically different groups of the leaf rust fungus are present in South America. The collections of Puccinia triticina from South America were tested with DNA molecular markers and also for their virulence to leaf rust resistance genes in wheat. Both the DNA markers and virulence markers can be used to classify rust collections. There were five distinct groups of Puccinia triticina in South America. Two of the groups comprised the large majority of the leaf rust that is currently present in South America. The five groups from South America were also compared for DNA markers and virulence to leaf rust resistance genes with six distinct groups of the leaf rust fungus that have been described in North America. Four of the groups from South America were nearly identical for DNA markers compared to the groups in North America, which indicated that these groups in both North and South America were highly related. The leaf rust groups in North and South America were likely both introduced from common sources in Europe, which may account for their high similarity. Also there is evidence that the same groups of leaf rust has recently been introduced to both North and South America from Mexico.
Technical Abstract: Leaf rust, caused by Puccinia triticina is the most prevalent and widespread disease of wheat in South America. The objective of this study was to determine the number of genetically differentiated groups of P. triticina that are currently present in South America, and to compare the South American population with the previously characterized population in North America. In total, 130 isolates of P. triticina from the wheat growing regions of Argentina, Brazil, Chile, Peru, and Uruguay mostly from the 1990s-2008 were 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. After removal of isolates with identical virulence and SSR genotypes, 99 isolates were included for further analysis. Principal coordinate analysis plots indicated five different groups of isolates based on SSR genotypes that also differed for virulence to leaf rust resistance genes. All pairs of groups, except for one pair, were significantly differentiated for SSR genotypes according to RST statistics. All but two pairs of groups were significantly differentiated for virulence phenotype according to FPT statistics. Isolates in all five groups had high values of FIS for SSR alleles and linkage disequilibrium was high across all isolates that indicated the clonal reproduction of urediniospores. Only one of the five P. triticina groups from South America was differentiated for SSR genotypes from all of the six P. triticina groups from North America. The high degree of similarity for SSR genotype of isolates from both South America and North America suggested a common European origin of P. triticina that was introduced to both continents. The emergence of the same P. triticina virulence phenotypes with highly related SSR genotypes in the U. S. in 1996 and in Uruguay in 1999 indicated the likely intercontinental migration of these genotypes from Mexico to both South America and North America.