- Rust Issues: All three rusts (stem, leaf and yellow rust) are serious constraints to wheat production.
- Ug99 Status: Three variants of Ug99 (PTKST, TTKST, TTKSK) have been deteced in Eritrea. PTKST, TTKST were first detected in Eritrea in 2010, both variants have combined virulence to Sr31 and Sr24. Race TTKSK was first detected in 2012.
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.
Annual rust surveys, led by Asmelash Wolday of NARI, during the period 3-15th October 2013 covered all the main wheat growing regions of Eritrea. A total of 69 sites were surveyed (see survey map – http://rusttracker.cimmyt.org/?page_id=1518).
As in previous years, stem rust predominated on the Eritrea surveys and the disease was widespread throughout the survey area. High frequency of stem rust in Eritrea has been a consistent trend for the last four years (see Fig. 1), only the drought year of 2009 stands out as being rust free. In 2013, stem rust was observed at 63 of the 69 sites surveyed (91%) with most sites (n=59) recording moderate (20-40%) or high (>40%) disease severity. A range of cereal crops were infected with stem rust, including; bread wheat, durum wheat, barley and wild oats. Extensive sampling was undertaken and samples are currently undergoing analysis at AAFC, Winnepeg, Canada and the Cereals Disease lab, Minnesota, USA.
Leaf and yellow rust were also widespread in Eritrea in 2013. Leaf rust was recorded at 49 of the sites surveyed (71%), with most sites (n=44) recording high (>40%) disease severity. Yellow rust was recorded at 33 of the sites surveyed (48%), with moderate or high disease severity recorded at 30 of the infected sites. Several yellow rust samples were collected and are currently undergoing analysis at the Global Rust Reference Center, Denmark.
Surveys undertaken by Dr Asmelash Wolday of NARI in the highland wheat growing areas of Eritrea during October 2012 found all three wheat rusts (stem, leaf and yellow) to be widespread. Stem rust was the predominant rust observed on the surveys. Stem rust was recorded at 77 of the 102 survey sites (75%), with moderate or high (>20%) severity recorded at 45 of the 77 confirmed sites (58%). Leaf rust exhibited a similar distribution pattern, being observed at 51 out of the 102 survey sites (50%). Moderate or high (>20%) severity of leaf rust was observed at 48 of the 51 sites (94%) where leaf rust was present. Yellow rust was also recorded at 51 out of the 102 survey sites (50%), with moderate or high (>20%) severity observed at 41 out of the confirmed 51 sites (80%).
Stem rust samples collected on the surveys were analysed using SNP marker diagnostics by Dr Les Szabo at the USDA-ARS, Cereals Disease Lab, Minnesota. A total of 23 samples were tested, with 1 sample being positive for the Ug99 race group stage 1 assay and postulated to be race TTKSK in the stage 2 assay. This is the first time that race TTKSK has been reported in Eritrea. The majority of the samples tested (n=18) were found to be non Ug99 races and for 4 samples inconclusive results were obtained.
Analysis undertaken by AAFC, Canada on stem rust samples collected by NARI, Eritrea in Oct. 2011 has confirmed the continued presence of Ug99 lineage race PTKST in Eritrea, but only 1 sample out 15 was typed to this race. All other samples analysed were found to be “J races” (JRCSC (n=2), JRHSC (n=4), JRHSF (n=8)) these are all virulent on Sr13 and probably came from durum wheat. A set of samples of stem rust from Oats was collected and analysed. The Oat results were interesting, two races were identified NHFC (n=11) and NKFC (n=3), all the isolates were clearly high on genes Pg10 and Pg16. It is believed that this virulence is not present anywhere else in the world except Australia.