A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>
In this posting:
 South Africa, Zimbabwe
Date: May 2012
Source: Plant Disease [edited]
[reference: PD Olivera, et al. Races of _Puccinia graminis_ f. sp.
_tritici_ with combined virulence to Sr13 and Sr9e in a field stem rust screening nursery in Ethiopia. Plant Dis 2012; 96, 623-628; DOI:
North American durum [hard wheat] lines, selected for resistance to TTKSK (Ug99) and related races of _Puccinia graminis_ f. sp. _tritici_ in Kenya, became susceptible in Debre Zeit, Ethiopia, suggesting the presence of stem rust races that were virulent to the TTKSK-effective genes in durum.
In the Debre Zeit nursery, 3 races were identified: JRCQC, TRTTF, and TTKSK. Both races JRCQC and TRTTF possess virulence on stem rust resistance genes Sr13 and Sr9e, which may explain why many TTKSK-resistant durum lines tested in Kenya became susceptible in Debre Zeit. The Sr9e-Sr13 virulence combination is of particular concern because these 2 genes constitute major components of stem rust resistance in North American durum cultivars. In addition to Sr9e and
Sr13 virulence, race TRTTF is virulent to at least 3 stem rust resistance genes that are effective to race TTKSK, including Sr36, SrTmp, and resistance conferred by the 1AL.1RS rye translocation.
Race TRTTF is the first known race with virulence to the stem rust resistance carried by the 1AL.1RS translocation, which represents one of the few effective genes against TTKSK in winter wheat [soft wheat] cultivars in the US.
Durum entries exhibiting resistant to moderately susceptible infection response at Debre Zeit in 2009 were evaluated for reaction to races JRCQC, TRTTF, and TTKSK at the seedling stage. In all, 47 entries were resistant to the 3 races evaluated at the seedling stage, whereas 26 entries exhibited a susceptible reaction. These results suggest the presence of both major and adult plant resistance genes, which would be useful in durum-wheat-breeding programs.
A thorough survey of virulence in the population of _P. graminis_ f.
sp. _tritici_ in Ethiopia will allow characterization of the geographic distribution of the races identified in the Debre Zeit field nursery.
 South Africa, Zimbabwe
Date: April 2012
Source: Plant Disease [edited]
[reference: ZA Pretorius, et al. First report of a new TTKSF race of wheat stem rust (_Puccinia graminis_ f. sp. _tritici_) in South Africa and Zimbabwe. Plant Dis 2012; 96, 590; DOI:
Seven races have been described in the Ug99 race group of _Puccinia graminis_ f. sp. _tritici_. Ug99-related races previously recorded in South Africa are TTKSF, TTKSP, and PTKST.
In December 2010, severe stem rust infection of the winter wheat cv.
Matlabas was observed for the 1st time in South Africa. Race analysis using the 20 North American stem rust differential lines classified the race as TTKSF. In comparative infection studies, Matlabas was susceptible to isolate UVPgt61/1 (TTKSF+) collected from Afrikaskop in the eastern Free State, whereas the cultivar was resistant to isolates
2013 (TTKSF), UVPgt55 (TTKSF), UVPgt59 (TTKSP), and UVPgt60 (PTKST).
Isolate 2013 represents the original collection of race TTKSF in South Africa.
Analysis showed that all single pustule isolates established from the original Matlabas isolate formed part of the Ug99 group [and] shared an identical genotype that differed from UVPgt55 (TTKSF), a foreign introduction into South Africa. Genotype analysis suggests that
UVPgt61/1 is genetically dissimilar to UVPgt55, as is Zim1009, another
TTKSF+ isolate that was collected from Birchenough in Zimbabwe.
Studies are under way to determine the identity of the defeated Sr gene in Matlabas and the cultivar has been added to the South African stem rust differential set.
TTKSF+ is the 8th race detected in the Ug99 group. Since no other
cultivars or advanced lines were found to carry the Matlabas gene, it is unlikely that race TTKSF+ will threaten wheat production in South Africa. However, the occurrence of a new Ug99-related race emphasizes the variability within this internationally important group.
[Wheat stem rust is caused by the fungus _Puccinia graminis_ f. sp.
_tritici_. Overall yield losses of up to 80 per cent are reported, but some fields are totally destroyed. Stem rust spores are spread by wind and with infected straw. Some grasses or volunteer wheat may generate a "green bridge" providing inoculum for the next cropping season.
Disease management may include fungicide applications, control of volunteer wheat, and resistant varieties if available.
New races are emerging, and the most dangerous at present is strain
Ug99 (discovered in Uganda in 1999, see ProMED-mail post 19990519.0812), which has overcome the major resistance gene Sr31 used in our current wheat varieties. Since then Ug99 has spread and even more virulent variants able to overcome additional resistance genes have emerged. Breeding programmes have been set up in international cooperation (Delhi Declaration) to establish wheat varieties resistant to Ug99 strains.
Ug99 group strains (that is, strains with Sr31 virulence) overcoming additional host resistance genes and/or with added fungicide resistances have emerged. Such strains are even more difficult to control and counteract the resistance breeding efforts. Ug99 strains were reported from southern Africa for the 1st time in 2009 opening up additional routes of transmission and increasing the threat in the southern hemisphere (ProMED-mail post 20100602.1834).
Several different systems exist for race nomenclature of stem rust and so far there is no single standard unified system (see link below for explanation of current nomenclature). The letter codes for the races above result from the North American system.
Hard (durum) wheats (_Triticum turgidum_, used for example for pasta) and winter (soft) wheats (_T. aestivum_, used mostly for bread) referred to in item  above are different species and may therefore show different levels of susceptibility to pathogen strains.
Provinces of South Africa:
<http://www.africa.upenn.edu/CIA_Maps/Zimbabwe_19893.gif> and <http://healthmap.org/r/1AY4> Provinces of Zimbabwe:
Stem rust symptoms on wheat:
Effects of Ug99 on resistant and susceptible wheat cultivars:
Information on wheat stem rust:
Information on Ug99:
<http://www.pestalert.org/viewNewsAlert.cfm?naid=36>, and <http://www.agbioworld.org/newsletter_wm/index.php?caseid=archive&newsid=2686>
Stem rust race nomenclature:
_P. graminis_ f. sp. _tritici_ taxonomy:
Global Rust Initiative:
<http://www.globalrust.org/>. - Mod.DHA]
Wheat stem rust, Ug99 group - Zimbabwe, Mozambique: new races
Wheat stem rust, Ug99 - Kenya: (RV), update 20101103.3976 Wheat stem rust, Ug99 group: new races 20100602.1834
Stem rust, wheat - India: new strain 20090717.2548 Wheat stem rust, strain Ug99: resistance breeding 20090326.1168 Wheat rusts - Kenya, India, Australia 20090312.1019
Wheat stem rust Ug99 - Australia ex Ethiopia: interception
Wheat stem rust, strain Ug99 - multicountry: update 20081120.3660 Wheat stem rust, strain Ug99 - Iran: 1st rep, alert 20080307.0925
Wheat stem rust, strain Ug99 - Kenya: new variant 20071217.4054 Wheat stem rust, strain Ug99 - multistate: resistance screening
Barley yellow dwarf virus & stem rust, cereals - Kenya 20070705.2132 Wheat stem rust, strain Ug99 - Yemen (02): government response
Wheat stem rust, spread: FAO, Global Rust Initiative 20070414.1241 Wheat stem rust, strain Ug99 - Yemen: 1st report 20070117.0229
Wheat stem rust, strain Ug99 - Pakistan: susp., 1st report
Stem rust, wheat - multicountry: new strains 20060406.1039
Wheat stem rust, Ug99, new strain - East Africa 20050928.2849 Wheat stem rust, new strain - Uganda 20050912.2698
Wheat stem rust fungus, new virulence genes - So Afr 20020814.5049
Wheat stem rust in resistant wheat lines - Uganda 20000702.1092
Stem-rust fungus, mutant, wheat - Uganda 19990519.0812]