Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2005
Publication Date: 10/28/2005
Citation: Wanyera, R., Kinyua, M.G., Jin, Y., Singh, R. 2005. The spread of Puccinia graminis f. sp. tritici with broad virulence in Eastern Africa. Plant Disease. 90:113. Interpretive Summary: Stem rust resistance in wheat worldwide has been effective and stable for a long period of time. In 2003 and 2004, a majority of current Kenyan cultivars and a large portion of CIMMYT wheat germplasm planted in Kenya became susceptible to stem rust. A study was conducted to characterize stem rust isolates from Kenya. The isolates were identified to belong to race TTKS, a virulence combination that has not been observed previously. These isolates were found to be virulent on winter wheat cultivars Custer, Foster, GA-Dozier, Patton, and Pioneer 26R61, and on SrWld-1, a gene used in spring wheat for its broad resistance to North American stem rust isolates. Results from this study indicated that stem rust isolates with virulence on Sr31 are now spread in the Eastern Africa highlands and pose a threat to wheat production in the region as well as other wheat production areas where Sr31 resistance is important. Many stem rust resistance genes, including Sr13, 22, 24, 25, 26, 27, 29, 32, 33, 35, 37, 39, 40, and 44, were found to be effective against TTKS. A rapid deployment of effective resistance genes in breeding is needed to reduce this threat.
Technical Abstract: Stem rust resistance in wheat worldwide has been effective and stable for a long period of time. Isolates of Puccinia graminis f. sp. tritici with virulence to Sr31, a gene used as the main component for stem rust resistance in many currently grown wheat cultivars worldwide, were detected in Uganda in 1999. In 2003 and 2004, many CIMMYT wheat lines planted in Kenya were susceptible to stem rust. A study was conducted to characterize the virulence of stem rust isolates from Kenya that overcame the resistance in CIMMYT wheat. Six isolates collected during 2004 at different locations were tested on the 16 stem rust race differential lines and an extended set of designated Sr genes at the seedling stage. All isolates from Kenya were virulent on Sr31 and were identified as TTKS. Stem rust resistance genes that are effective against TTKS at the seedling stage include Sr13, 22, 24, 25, 26, 27, 29, 32, 33, 35, 36, 37, 39, 40, 44, and Tmp, most of which are of alien origin. Single-gene lines carrying Sr25, 26, 29, and 44, did not confer adequate level of resistance in the adult plant stage. The virulence spectrum of the Kenyan isolates was identical to that of an isolate collected from Uganda in 1999 with virulence on Sr31, indicating that this race is now widespread in the Eastern Africa highlands and may pose a threat to wheat production in the region as well as other wheat production areas where Sr31 resistance is important. A rapid deployment of effective resistance genes in breeding is needed to reduce this threat.