New disease may cause tremendous crop losses in Africa and Asia

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Stripe rust threat to wheat worse than predicted
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An epidemic caused by a new strain of wheat fungus could cause billions of dollars in crop losses across North Africa, the Middle East, and Central Asia. The wheat stripe rust epidemic is far worse than predicted, scientists have found. "Some farmers will suffer 30-60 percent yield loss. In the worst cases, yield loss is 100 percent," said Maarten Van Ginkel, International Center for Agricultural Research in the Dry Areas (ICARDA).

Key cereal production regions are affected and in some countries, like Syria, up to 80 percent of fields are affected. "Urgent action is needed to protect wheat crops on some 50 million hectares [124 million acres]," Mahmoud Solh, director general of ICARDA, said. The areas most affected by the stripe rust include Iran, Iraq, Morocco, and Syria. Afghanistan, Algeria, and Tunisia are also affected.

The pathogen race able to overcome a major wheat resistance gene first emerged in 2002 in South Asia but unfavourable weather conditions limited its spread until 2009, when it started re-appearing. Van Ginkel said his team is documenting and analysing the impact of the recent outbreaks.

New resistant wheat varieties are already available. But the process of releasing these varieties and distributing enough seeds must be accelerated. Governments will have to take appropriate measures, such as planting high-yielding, resistant varieties and continually monitoring affected areas, to prevent new outbreaks in 2011, Solh said. "ICARDA has always stressed the need to remain vigilant against stripe rust."

[Byline: Safaa Kanj]

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[Stripe rust (also called yellow rust) of cereals is caused by the fungus _Puccinia striiformis_ var. _striiformis_. It causes yellow leaf stripes and stunting of plants with yield losses of 40 to 100 percent. The disease affects wheat, some barley varieties, triticale, and a number of wild grasses. Spores are wind dispersed in several cycles during the cropping season, and the fungus survives on living host plants generating a "green bridge" between seasons. Disease management includes the use of resistant varieties, fungicide applications, and control of volunteer crops.

New stripe rust strains with increased virulence have been reported in recent years from Europe, North America, Australia, and India and are also suspected to emerge in China. Monitoring programmes are important to recognise these emerging new strains. Depending on the susceptibility of preferred cereal varieties grown in different countries, it can be expected that new rust strains will differ in national or regional significance.