Kenyan isolates of Puccinia graminis f. sp. tritici from 2008 to 2014: Virulence to SrTmp in the Ug99 race group and implications for breeding programs
Newcomb, M., Olivera, P.D., Rouse, M.N., Szabo, L.J., Johnson, J., Gale, S., Luster, D.G., Wanyera, R., Macharia, G., Bhavani, S., Hodson, D., Patpour, M., Hovmøller, M.S., Fetch, T.G., Jin, Y. (2016). Kenyan isolates of Puccinia graminis f. sp. tritici from 2008 to 2014: Virulence to SrTmp in the Ug99 race group and implications for breeding programs. Phytopathology, [online] 106(7), 729-736. http://dx.doi.org/10.1094/PHYTO-12-15-0337-R
Plain language summary
There are new strains of wheat stem rust fungus emerging in Africa that threaten the Canadian wheat production if they migrate. Thus it is necessary to survey and sample infected wheat to determine if newer strains are developing. In Kenya in 2013 and 2014 we surveyed infected wheat fields and took samples to determine if the strains are old ones or new ones. Our work found that indeed there were three new strains of the Ug99 stem rust ancestry. One strain (TTKTT) could attack 23% of advanced Kenya wheat lines and up to 91% of wheat lines from North America. This indicated that new rust strains with increased ability to attack wheat are developing in Kenya, and continued work to do surveillance for new strains of wheat stem rust must continue.
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.