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Title: Genotyping of U.S. wheat germplasm for presence of stem rust resistance genes Sr24, Sr36 and Sr1RSAmigo

Author
item OLSON, E - North Carolina State University
item Brown-Guedira, Gina
item Marshall, David
item JIN, Y - University Of Minnesota
item MERGOUM, M - North Dakota State University
item LOWE, I - University Of California
item DUBCOVSKY, J - University Of California

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2009
Publication Date: 1/28/2010
Citation: Olson, E.L., Brown Guedira, G.L., Marshall, D.S., Jin, Y., Mergoum, M., Lowe, I., Dubcovsky, J. Genotyping of U.S. wheat germplasm for presence of stem rust resistance genes Sr24, Sr36 and Sr1RSAmigo. Crop Science. 50:668-675. 2010.

Interpretive Summary: The stem rust fungus has historically caused dramatic yield losses in cultivated wheat. Stem rust posed a major threat to wheat production in the United States in the early twentieth century with major epidemics occurring between 1900 and the 1950s. Efforts to remove the alternate host, common barberry and the development of lines possessing genes for resistance led to a decrease in the number and magnitude of stem rust epidemics in the U.S.. In 1999, a novel highly virulent stem rust race, reported as Ug99, was identified in Uganda that has spread to neighboring countries. The potential global dispersal of this uniquely virulent pathogen makes the development of resistant cultivars quite urgent. There are modlecular markers available that tag the stem rust resistance genes Sr24, Sr26, Sr36, and Sr1RSAmigo that confer resistance to Ug99. A collection of 776 cultivars and breeding lines of wheat from all growing regions of the United States were screened with DNA markers associated with Sr24, Sr26, Sr36, and Sr1RSAmigo to determine frequencies of these genes in U.S. wheat germplasm. The precision of the DNA markers at predicting the presence of these genes was evaluated via comparison with data from infecting seedlings with the pathogen. Among the lines evaluated, the most predominant gene is Sr24, present in hard winter, hard spring, and soft winter wheat lines. Resistance in soft winter wheat is primarily due to Sr36. The 1RS·1AL rye translocation carrying Sr1RSAmigo is present at equal frequencies in hard winter and soft winter wheat. The Sr26 gene was not found in any lines evaluated. Utilization of marker assisted selection for stem rust resistance genes can hasten the development of wheat cultivars resistant to Ug99 and its variants and allow for the development of resistance gene pyramids for more durable stem rust resistance.

Technical Abstract: The stem rust resistance genes Sr24, Sr26, Sr36, and Sr1RSAmigo confer resistance to race TTKSK (= Ug99) of Puccinia graminis f.sp. tritici (Pgt). A collection of 776 cultivars and breeding lines of wheat (Triticum aestivum L.) from all growing regions of the United States were screened with simple sequence repeat (SSR) and sequence tag site (STS) markers linked to Sr24, Sr26, Sr36, and Sr1RSAmigo to determine frequencies of these genes in U.S. wheat germplasm. Marker efficacy in predicting the presence of these genes was evaluated via comparison with assayed seedling infection type. Among the lines evaluated, the most predominant gene is Sr24, present in hard winter, hard spring, and soft winter wheat lines. Resistance in soft winter wheat is primarily due to Sr36. The 1RS·1AL rye translocation carrying Sr1RSAmigo is present at equal frequencies in hard winter and soft winter wheat. Utilization of marker assisted selection for stem rust resistance genes can hasten the development of wheat cultivars resistant to TTKSK and its variants and allow for the development of resistance gene pyramids for more durable stem rust resistance.