New variants in the Ug99 race group found in Kenya in 2013 and 2014

Since 1998, when Pgt race TTKSK (Ug99) was first identified in Uganda, seven variants in the Ug99 race group have been reported in nine countries in eastern and southern Africa. Five of these variants (TTKSK, TTKST, TTTSK, PTKSK, and PTKST) have been observed in Kenya. Increased surveillance efforts in recent years have enabled detection of new virulence combinations that threaten wheat production. Three new variants in the Ug99 race group were identified from samples collected in 2013 and 2014 in Kenya. A new race, TTHST that is identical to TTKST but avirulent on Sr30 (IT 2-), was identified from a sample collected in the Central Rift Valley Region in 2013. In 2014, two new races, TTKTK and TTKTT, were identified from a total of nine samples (six collected from cv. Robin, and one from each of Eagle10, NJRBW II, and barley) in multiple regions. These two races are of special concern as both are virulent on SrTmp, a gene that is effective against all previously known races in the Ug99 group. Resistance gene SrTmp is postulated to be the source of TTKSK resistance in cv. Robin (released in 2011 in Kenya, also postulated to have Sr2) and cv. Digalu (released in 2005 in Ethiopia). The presence of new races with virulence on SrTmp may explain the high levels of stem rust severity observed in wheat cultivar Robin in Kenya in the past two years. Genotypic relationships between these new races and known races in the Ug99 race group are being characterized using SNP markers. Cultivars and elite breeding lines from Kenya, CIMMYT, and the US are being evaluated for seedling reactions to race TTKTT. With the detection of these new races, there are a total of eight variants in the Ug99 race group in Kenya.

Maria Newcomb
USDA-ARS Arid Land Agricultural Research Center
P. Olivera, R. Wanyera , S. Gale3, D. Luster , S. Bhavani , M. Rouse , L.J. Szabo and Y. Jin
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