Analysis of dead, single pustule stem rust pathogen samples (D-samples) using molecular diagnostic SNP assay at the USDA-ARS Cereals Disease Lab, Minnesota has detected a race TKTTF (“Digalu” race) genotype in Kenya for the first time. Five samples from 2014 and 7 samples from 2015, all collected by Ruth Wanyera and the pathology team from KALRO, Njoro, tested positive for race TKTTF genotype. These results indicated that a single genotype (clade IV-B) was present in Kenya. Clade IV-B is the predominant genotype in Ethiopia.
The D-sample results indicate that race TKTTF is distributed (probably at low frequency) throughout the major wheat growing regions of Kenya. The 2014 positive samples were collected from North Rift (n=2), Central Rift (n=1) and Mount Kenya (n=2). In 2015, positive samples were collected from South Rift (n=1), Central Rift (n=1) and Mount Kenya (n=5). Most of the TKTTF genotype positive samples were collected from the cultivar ‘Robin’ (n=9), but ‘KS Mwamba’ (n=1), ‘Kwale’ (n=1) and an unknown barley variety (n=1) also produced positive results for TKTTF genotype.
At present no race analysis studies on live samples collected in Kenya have detected the presence of race TKTTF. Testing of the SNP assay against known isolates of TKTTF and negative controls has proven 100% reliable, but until there is confirmation by race analysis the D-sample results are considered indicative.
Race TKTTF now totally dominates the stem rust pathogen population in all the wheat growing regions of neighbouring Ethiopia, so its presence in Kenya is not unexpected.