May 5, 2011
Source: SciDevNet
Mahmoud Solh, Shivaji Pandey, Thomas Lumpkin, Ronnie Coffman
Developing countries need help with crop surveillance and the development of strains resistant to wheat rust, say agricultural research leaders.
Today's food security situation is being worsened by strains of wheat rust disease that are emerging more frequently and spreading much faster and to new areas — changes fuelled by climate change and conducive environments in increasingly fragile ecosystems.
Perhaps the most problematic wheat diseases are the two kinds of wheat rust: stripe rust (also called yellow rust) and stem rust (black rust).
To protect their crops from the fungus that causes wheat rust, countries need to take pre-emptive action with sustained investment in research, surveillance, a strategy to boost crop diversity, and policies to encourage farmers to adopt disease-resistant crop varieties.
Rust epidemics
A new form of stem rust known as Ug99 took several growing seasons to spread from the highlands of Uganda and Kenya in 1999, via Ethiopia and Yemen, to reach Iran by 2007. The disease could spread even farther — from Iran to the vast wheat fields in Turkey, Afghanistan, Pakistan and India, which are largely sown with varieties not resistant to Ug99.
Stripe rust is also prevalent in most of the world's major wheat-growing areas. In the past 30 years, it has caused severe economic losses to crops in North America, Europe, Australia, Central Asia, West Asia, South Asia and North Africa. The losses ranged from 30 to 50 per cent of the expected grain yield of a country's wheat production. And last season, an epidemic of a virulent new kind of stripe rust caused wheat losses of up to 40% in Western Asia.
Epidemics of stripe rust in the 1980s — caused by a strain that overcomes resistance in many wheat varieties — spread from East Africa to the Middle East, Turkey, Iran, Afghanistan, Pakistan and India. They affected major wheat-growing regions and hit the livelihoods of millions of farmers.
In the following years, researchers released varieties of wheat that were resistant to this strain in most of these areas. But many of these varieties are susceptible to the new strain of stripe rust that began to spread last season and continues to spread rapidly. This aggressive new strain, called YR27, is tolerant of higher temperatures and adapts rapidly to new environmental conditions.
Growing threat
The threat of a repeat of the 1980s epidemic is growing, and scientists who track wheat rust pathogens are warning countries to be prepared.
An epidemic in these wheat-dependent countries could cost billions of dollars, creating a further spike in food prices, reducing food security and causing political tensions. Developing countries are stepping up their efforts in surveillance and research on breeding wheat for rust resistance.
For example, networks of scientists and agriculture specialists are exchanging information for an early warning of rust incidence in their area; scientists are using 'slow-rusting' genes to extend the time that varieties can resist the disease in a bid to slow down the progression of epidemics; and farmers are avoiding covering large areas with wheat varieties with similar genetic backgrounds and degrees of resistance.
Although researchers can build disease resistance into wheat, this typically involves a ten-year cycle from development to the release of new varieties.
And while breeding programmes continuously develop resistant varieties, fungicides can be used to control wheat rust in cases of emergency. But this option is not generally affordable for resource-poor farmers, and fungicides are not environmentally friendly.
Sustained investment
Can wheat rust be eradicated? Norman Borlaug, the father of wheat improvement in the 1960s, noted that "rust never sleeps". Rust strains will continue to mutate and overcome crop resistance.
Rather than reacting to food crises, sustained investment is needed to support agricultural research and preparedness to help countries better manage rust problems in the long term.
Donor governments, development agencies and the international research community must increase their attention and support to low-income countries striving to develop strategies to prevent wheat rust. And those countries need robust food-security strategies that include sharing information on crop breeding across regions.
Increased surveillance — both national and regional — involves testing and tracking rust types using geospatial tools, monitoring the wheat varieties they attack and determining which are resistant. Susceptible varieties can then be replaced by resistant ones.
In Iran, for example, a monitoring network of agricultural extension specialists and researchers gathered reports of new strains that prompted the country's plant protection authorities to stock up on fungicide, and establish a nursery testing rust samples sent in by wheat breeders. This helped scientists identify 10 varieties resistant to a strain of stripe rust over the past three years, which were then prepared and distributed to farmers.
Wheat-producing countries must also be encouraged to design agricultural systems that enable new seed varieties to be released and multiplied faster. In Egypt, for example, such a system has led to the production of new resistant varieties that can cover 30% of the country's wheat-growing area in just three years. These varieties often offer better quality and higher yields — a powerful incentive for farmers to adopt them.
Faced with the threat of wheat rust epidemics, the solution for low-income countries and the development partners that support them is to adopt a combined strategy of continued disease surveillance, development and dissemination of new resistant varieties, strengthening research capacity, and ensuring that farmers adopt and multiply new seeds.
Mahmoud Solh is director general of the International Center for Agricultural Research in the Dry Areas (ICARDA). Shivaji Pandey is director of the UN Food and Agriculture Organization. Thomas Lumpkin is director general of the International Maize and Wheat Improvement Center (CIMMYT). Ronnie Coffman is vice-chair of the Borlaug Global Rust Initiative (BGRI).
Photo: Flickr/CIMMYT
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