Current spread of the Ug99 strain of Puccinia graminis f.sp. tritici in Africa and Asia
Black stem rust caused by Puccinia graminis f.sp. tritici is a worldwide disease of wheat with a long history. Rusts were already occurring on cultivated cereals during the Bronze Age, and they have caused very severe crop losses until the middle of the 20th century. Concerning black stem rust, control measures which had progressively been put into place (destruction of the alternate host Berberis vulgaris and the use of resistant cultivars) have maintained the disease at very low levels in most countries. In Europe, the disease was observed sporadically until 1980 in France and Switzerland on old wheat cultivars, as well as in a few Southern and Eastern European countries which were not using modern resistant varieties. However, in 1999 a new virulent strain of P. graminis f.sp. tritici was observed in Uganda on wheat varieties which were previously considered to be resistant to the disease (i.e. varieties carrying resistance genes Sr31 and Sr38). This new strain was called Ug99 to recall the year and country of first discovery. Ug99 then spread to other East African countries (Kenya in 2001, Ethiopia in 2003) causing very severe damage. It continued to spread eastwards to Sudan, and then jumped over the Red Sea to reach Yemen in the Middle East. In early 2008, Ug99 was discovered in Iran. The anticipated spread of Ug99 poses a risk for the whole world production of wheat. For the EPPO region, it might be considered that it poses a more immediate risk to countries in the Near East (Israel, Turkey), the Caucasus (Armenia, Azerbaijan, Georgia) and Central Asia (Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan), but other parts of the region are also at risk.
Stem rust produces huge numbers of urediniospores during the crop season which are dispersed by the wind over long distances and across continents. These spores can also be transported by travellers’ clothing or infected plant material. Considering the biology of this disease, quarantine measures are not considered adequate. However, as international cooperation is needed to protect wheat production at a global level, FAO, CIMMYT, and BGRI (Borlaug Global Rust Initiative) are currently coordinating the development of management strategies. The main elements to control Ug99 include: disease surveillance, breeding for durable resistance, seed multiplication and distribution of resistant cultivars, and field management (e.g. different planting dates, adequate use of fungicides).
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INTERNET (last accessed 2008-07)
Borlaug Global Rust Initiative (BGRI) website. http://www.globalrust.org
CIMMYT website. Ug99 – RustMapper. http://www.cimmyt.org/GIS/RustMapper/Index.htm
Hodson DP, Singh RP, Dixon JM (2007) An initial assessment of the potential impact of stem rust (race Ug99) on wheat producing regions of Africa and Asia using GIS. http://www.cimmyt.org/gis/pdf/UG99postH.pdf
FAO NewsRoom, Rome, 2008-03-05. Wheat killer detected in Iran. Dangerous fungus on the move from East Africa to the Middle East. http://www.fao.org/newsroom/en/news/2008/1000805/index.html