Phenotypic and genotypic characterization of race TKTTF of Puccinia graminis f. sp. tritici that caused a wheat stem rust epidemic in southern Ethiopia in 2013-2014

Authors: OLIVERA, PABLO - University Of Minnesota; NEWCOMB, MARIA - University Of Minnesota; Szabo, Les; Rouse, Matthew; Johnson, Jerry; HODSON, DAVID - International Maize & Wheat Improvement Center (CIMMYT); Luster, Douglas - Doug; COX, JAMES - University Of Cambridge; BURGIN, LAURA - University Of Cambridge; GILLIGAN, CHRISTOPHER - University Of Cambridge; PATPOUR, MEHRAN - Aarhus University; HOVMOLLER, MOGENS - Aarhus University; WOLDEAB, GETANEH - Ethiopian Agricultural Research; HAILU, ENDALE - Ethiopian Agricultural Research; HUNDIE, BEKELE - Ethiopian Agricultural Research; TADESSE, KEBEDE - Washington State University; PUMPHREY, MICHAEL - Washington State University; SINGH, RAVI - International Maize & Wheat Improvement Center (CIMMYT); Jin, Yue

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2015
Publication Date: 3/4/2015
Citation: Olivera, P., Newcomb, M., Szabo, L.J., Rouse, M.N., Johnson, J.L., Hodson, D., Luster, D.G., Cox, J., Burgin, L., Gilligan, C., Patpour, M., Hovmoller, M., Woldeab, G., Hailu, E., Hundie, B., Tadesse, K., Pumphrey, M., Singh, R., Jin, Y. 2015. Phenotypic and genotypic characterization of race TKTTF of Puccinia graminis f. sp. tritici that caused a wheat stem rust epidemic in southern Ethiopia in 2013-2014. Phytopathology. 105(7):917-928.

Interpretive Summary: Ethiopia is the largest wheat producer in sub-Saharan Africa, and wheat is a traditional staple food crop for the country. A severe stem rust epidemic occurred in Ethiopia during November 2013 to January 2014, with yield losses close to 100% on the most widely grown bread wheat cultivar, 'Digalu'. Field surveys were undertaken to determine the affected areas and the causal races of the stem rust pathogen, Puccinia graminis f. sp. tritici. A meteorological model for airborne spore dispersal was used to inform the selection of sampling locations by identifying which regions were most likely to have been infected from postulated sites of initial infection. Based on the analyses of 106 isolates derived from sixty-four samples, race TKTTF was found to be the primary cause of the epidemic in the southeastern zones of Bale and Arsi. Isolates of race TTKSK, a member of the Ug99 race group, were also found in the epidemic areas but at a low frequency. Genotyping indicated that isolates of race TKTTF belongs to a genetic lineage that is different from isolates of the Ug99 race group and is composed of two distinct genetic types. Results from evaluation of selected Ethiopian and CIMMYT germplasm indicated that some cultivars and breeding lines observed as resistant to isolates of Ug99 race group are susceptible to isolates of race TKTTF. Appearance of race TKTTF and the ensuing epidemic underlines the continuing threats and challenges posed by Puccinia graminis f. sp. tritici not only in East Africa, but also to wider scale wheat production.

Technical Abstract: A severe stem rust epidemic occurred in southern Ethiopia during November 2013 to January 2014 with yield losses close to 100% on the most widely grown wheat cultivar, 'Digalu'. Sixty-four stem rust samples collected from the regions were analyzed. A meteorological model for airborne spore dispersal was used to identify which regions were most likely to have been infected from postulated sites of initial infection. Based on the analyses of 106 single pustule isolates derived from these samples, four races of Puccinia graminis f. sp. tritici were identified: TKTTF, TTKSK, RRTTF, and JRCQC. Race TKTTF was found to be the primary cause of the epidemic in the southeastern zones of Bale and Arsi. Isolates of race TKTTF were first identified in samples collected in early October 2013 from West Arsi. It was the sole or predominant race in 31 samples collected from Bale and Arsi zones after the stem rust epidemic was established. Race TTKSK was recovered from 15 samples from Bale and Arsi zones at low frequencies. Genotyping indicated that isolates of race TKTTF belongs to a genetic lineage that is different from the Ug99 race group and is composed of two distinct genetic types. Results from evaluation of selected germplasm indicated that some cultivars and breeding lines resistant to the Ug99 race group are susceptible to race TKTTF. Appearance of race TKTTF and the ensuing epidemic underlines the continuing threats and challenges posed by stem rust not only in East Africa, but also to wider scale wheat production.