ARS | Publication request: An accurate DNA marker assay for stem rust resistance gene Sr2 in wheat

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 22, 2010
Publication Date: November 9, 2010
Citation: Mago, R., Brown Guedira, G.L., Dreisigacker, S., Breen, J., Jin, Y., Singh, R., Appels, R., Lagudah, E., Ellis, J., Spielmeyer, W. 2010. An accurate DNA marker assay for stem rust resistance gene Sr2 in wheat. Theoretical and Applied Genetics. 122:735-744.

Interpretive Summary: The stem rust fungus has historically caused dramatic yield losses in cultivated wheat and posed a major threat to wheat production in the United States in the early twentieth century. More recently, stem rust has been less of a threat due to use of resistant varieties. Wheat varieties having the resistance gene Sr2 have been grown for many decades and in many regions of the world. Although this gene confers partial resistance that is effective only in the adult plant stage, Sr2 is effective against all known races of stem rust including the recently described Ug99 race that can overcome most other stem rust resistance genes. Because Sr2 is an important resistance gene which is difficult to select, an accurate and robust DNA marker for Sr2 would benefit the wheat breeding community worldwide. Using DNA sequences derived from the vicinity of the Sr2 gene, we developed a DNA marker that could predict the presence or absence of the gene with 95% accuracy. Given the high level of accuracy observed, the marker provides breeders with a selection tool for one of the most important disease resistance genes of wheat.

Technical Abstract: The stem rust resistance gene Sr2 has provided broad-spectrum protection against stem rust (Puccinia graminis) since its wide spread deployment in wheat from the 1940s. Because Sr2 confers partial resistance which is difficult to select under field conditions, a DNA marker is desirable that accurately predicts Sr2 in diverse wheat germplasm. Using DNA sequence derived from the vicinity of the Sr2 locus, we developed a CAPS marker that is associated with the presence or absence of the gene in 115 of 122 (95%) diverse wheat lines. The marker genotype predicted the absence of the gene in 100% of lines which were considered to lack Sr2. Discrepancies were observed in lines that were predicted to carry Sr2 but failed to show the diagnostic CAPS marker. Given the high level of accuracy observed, the marker therefore provides breeders with a selection tool for one of the most important disease resistance genes of wheat.