|BAJGAIN, PRABIN - University Of Minnesota|
|Rouse, Matthew - Matt|
|BULLI, PETER - Washington State University|
|BHAVANI, SRIDHAR - International Maize & Wheat Improvement Center (CIMMYT)|
|WANYERA, RUTH - Kenya Agricultural Research Institute|
|NJAU, PETER - Kenya Agricultural Research Institute|
|LEGESSE, WASIHUN - Ethiopian Agricultural Research|
|ANDERSON, JAMES - University Of Minnesota|
|PUMPHREY, MICHAEL - Washington State University|
Submitted to: Biomed Central (BMC) Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2015
Publication Date: 10/14/2015
Citation: Bajgain, P., Rouse, M.N., Bulli, P., Bhavani, S., Gordon, T.C., Wanyera, R., Njau, P., Legesse, W., Anderson, J., Pumphrey, M. 2015. Association mapping of North American spring wheat breeding germplasm reveals loci conferring resistance to Ug99 and other African stem rust races. Biomed Central (BMC) Plant Biology. 15(249):1-19. doi: 10.1186/s12870-015-0628-9.
Interpretive Summary: Wheat stem rust is a fungal disease of wheat that decreases yield. A strain of the wheat stem rust fungus known as Ug99 emerged in Uganda in 1999 and threatens global wheat production, because of it's ability to infect nearly all wheat varieties. We identified several United States spring wheat breeding lines that possess partial resistance to Ug99 at the adult plant stage in Kenya and Ethiopia. We also identified several molecular markers that are associated with stem rust resistance in the current United States wheat breeding lines. The wheat breeding lines identified with partial resistance suggest that wheat breeders in the United States can obtain resistance to Ug99 by selecting within convential germplasm. The molecular markers that we identified as linked to stem rust resistance can also be used in wheat breeding to select for resistance to Ug99. The identification these molecular markers and resistant breeding lines will facilitate the improvement of resistance of United States wheat cultivars to the dangerous Ug99. Ug99 resistant wheat cultivars will protect United States wheat production from yield loss if a Ug99 epidemic were to occur in the United States.
Technical Abstract: The recently identified Puccinia graminis f. sp. tritici (Pgt) race TTKSK (Ug99) poses a severe threat to global wheat production because of its broad virulence on several widely deployed resistance genes. Additional concerning virulences have been detected in the Ug99 group of races, and spread of this race group has been documented across wheat growing regions in Africa and West Asia. Other broadly virulent Pgt races, such as TRTTF and TKTTF, present further difficulties in maintaining genetic resistance against this destructive fungal disease of wheat. In an effort to identify loci conferring resistance to these races, a genome-wide association study was carried out on a panel of 250 spring wheat breeding lines from the International Maize and Wheat Improvement Center (CIMMYT), and several wheat breeding programs in the United States and Canada. This germplasm panel was screened for adult plant resistance (APR) to Ug99 during 2013 and 2014 in artificial stem rust screening nurseries at Njoro, Kenya and at Debre-Zeit, Ethiopia. The lines were also screened for resistance at seedling stage against the races TTKSK, TRTTF, and TKTTF; and only 9 of the 250 lines were resistant as seedlings to all races. Using a mixed linear model, several markers associated with adult plant and seedling resistance were identified. In particular, markers linked with the APR gene Sr2 were identified and associated with field resistance; and markers linked to the genes Sr8a and Sr11 were identified for seedling resistance to the races TRTTF and TKTTF, respectively. Markers were also detected on chromosomes where no sources of resistance to these races have been reported previously. Our results demonstrate that the N. American wheat breeding lines have numerous resistance loci that provide APR and seedling resistance to highly virulent Pgt races. Using the resistant lines and the significant SNPs identified in this study in marker-assisted resistance breeding can assist in development of varieties with elevated levels of resistance to virulent stem rust races including TTKSK.