- Rust Issues: Yellow rust and stem rust are serious constraints to wheat production.
- Ug99 Status: Two Ug99 lineage races have currently been detected in Rwanda. Race TTKSK (Ug99) and race TTTSK (Ug99+Sr36) were detected in 2014. Race TTKSK predominates.
Combined results from race analysis undertaken at several different labs indicate that five new variants in the Ug99 lineage were detected from samples collected in East Africa during 2013 or 2014. Probably most significant were the two new SrTmp variants (Races TTKTK and TTKTT) previously reported (see “16 April 2015: BGRI report two new Ug99 variants with virulence to SrTmp detected in Kenya” and Patpour et al. 2015). Further analysis has revealed the presence of three additional new Ug99 lineage races. Details of these additional new races are:
- Race TTHST: Similar to race TTKST (Ug99 + Sr24 vir) but avirulent on Detected in Kenya in 2013 (1 isolate). Source lab: USDA-ARS Cereals Disease Lab, USA (Newcomb et al in prep)
- Race TTHSK: Similar to race TTKSK (Ug99) but avirulent on Detected in Kenya in 2014 (2 isolates). Source lab: AAFC Morden Research Centre, Canada (Fetch et al 2016)
- Race PTKTK: Similar to race PTKSK (Ug99 but avir on Sr21) but virulent on SrTmp. Detected in Kenya in 2014 (5 isolates). Source lab: AAFC Morden Research Centre, Canada (Fetch et al 2016)
These latest results bring the total of known variants within the Ug99 lineage to 13, with yet another SrTmp variant being detected in Kenya. All five of the new variants were detected in Kenya, but as previously reported race TTKTK was also detected in Uganda, Rwanda, Eritrea and Egypt in 2014. The results indicate that the Ug99 race group continues to evolve at a rapid rate.
Mehran Patpour (Global Rust Reference Center in Denmark) and co-authors have just published details of the emergence and spread of virulence to SrTmp in the Ug99 race group in Africa. The note is now available as a First Look in Plant Disease (see http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-06-15-0668-PDN). The report details the results of combined race analysis undertaken by the GRRC, Denmark and the USDA-ARS Cereals Disease Lab, Minnesota on 84 stem rust samples collected in 2014 from Kenya, Uganda, Rwanda and Egypt.
The presence of two new Ug99 race group variants – race TTKTK (Ug99 + virulent on SrTmp) and race TTKTT (Ug99 + virulent on SrTmp and Sr24) were confirmed in Kenya. Race TTKTK was also confirmed in Uganda, Rwanda and Egypt. Detection of these new variants in the Ug99 race group across several countries in a single year indicates the relevance of coordinated surveillance activities and also indicates potentially very rapid geographical dispersal of race TTKTK.
Following the recent surveys and sampling in Rwanda by the Rwanda Agriculture Board (RAB), wheat program and CIMMYT-Ethiopia during the period 27th Jan – 1st Feb 2014; two known Ug99 races have now been identified. Molecular diagnostic assays carried out by Dr Les Szabo at the USDA-ARS Cereals Disease Lab, Minnesota confirmed the presence of races TTKSK (original Ug99) and TTTSK (Sr36 variant of Ug99) in Rwanda. Race TTKSK was dominant, being identified in 13 samples from four dispersed locations (Kinigi RS, Rusarabuye, Rwerere RS and Sigira RS – see map). Two distinct genotypes of race TTKSK (AF-001aa and AF-001ad) were identified in the samples analysed. Race TTTSK (genotype AF-001cc) was detected in 2 samples collected at Sigira RS in the southern province. The results obtained from Rwanda make it the 12th country in which the Ug99 race group has been identified. The races and genotypes detected match those previously known from Uganda and Kenya, so are not unexpected. No evidence was found to indicate the presence of the race implicated in the recent stem rust epidemic in Ethiopia.
During the period 27th Jan – 1st Feb 2014 scientists from the Rwanda Agriculture Board (RAB), wheat program and CIMMYT-Ethiopia conducted wheat rust surveys and sampling in wheat growing areas of the Northern and Southern provinces. These surveys led by Innocent Habarurema (RAB) represent one of the first attempts to understand the status and population composition of wheat rusts in Rwanda. A total of 7 unique, dispersed locations (4 research stations and 3 farmer field sites – see Rwanda Survey Mapper) were included in the survey. Yellow rust and stem rust predominated; with yellow rust being recorded at all locations surveyed and stem rust recorded at all but one location. Leaf rust was not common, only recorded at one location. Disease pressure was higher on research stations vs farmer fields, especially for stem rust. Given the importance of the region for emerging new races of both stem and yellow rust, a key priority of the surveys was sampling to determine which races of rust are currently present in Rwanda. Another important reason for surveys was the spore dispersal modelling work, undertaken by Cambridge University, UK, from the recent stem rust outbreak in Ethiopia.
Model predictions of spore dispersal from the Ethiopia stem rust outbreak indicate the potential for spore movement in a south-westerly direction, with a very low probability that spores may travel as far as Rwanda. Although Rwanda is at very low risk of any spore dispersal from Ethiopia, monitoring of the rust situation in the country was considered a priority in light of this recent outbreak. A total of 14 stem rust samples (live samples plus corresponding DNA samples) and 13 yellow rust samples were collected. The samples aimed to be representative of different geographical areas and different cultivars grown. Samples are currently undergoing analysis at the Cereals Disease Lab, Minnesota, USA and the Global Rust Reference Centre, Denmark and results will be forthcoming.