Frequent emergence of new variants in the Puccinia graminis f. sp. tritici Ug99 race group in Kenya has made pathogen survey a priority. We analyzed 140 isolates from 78 P. graminis f. sp. tritici samples collected in Kenya between 2008 and 2014 and identified six races, including three not detected prior to 2013. Genotypic analysis of 20 isolates from 2013 and 2014 collections showed that the new races TTHST, TTKTK, and TTKTT belong to the Ug99 race group. International advanced breeding lines were evaluated against an isolate of TTKTT (Sr31, Sr24, and SrTmp virulence) at the seedling stage. From 169 advanced lines from Kenya, 23% of lines with resistance to races TTKSK and TTKST were susceptible to TTKTT and, from two North American regional nurseries, 44 and 91% of resistant lines were susceptible. Three lines with combined resistance genes were developed to facilitate pathogen monitoring and race identification. These results indicate the increasing virulence and variability in the Kenyan P. graminis f. sp. tritici population and reveal vulnerabilities of elite germplasm to new races.
Bibliographical noteFunding Information:
This research received support from the Durable Rust Resistance in Wheat project administrated by Cornell University and funded by the Bill and Melinda Gates Foundation and the United Kingdom Department for International Development, and from the USDA-ARS National Plant Disease Recovery Plan. We thank S. Stoxen, L. Wanschura, M. Carter, and the KALRO pathology team of H. Wanga, P. Kinyanjui, F. Muchika, E. Githinji, L. Wolukao, V. M. Onyango, and E. O. Okello for their technical contributions. Mention of trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval to the exclusion of other products and vendors that might also be suitable.