Experts have been aware of the threat since a major epidemic swept across North America’s wheat belt in the 1950s, destroying up to 40 per cent of the crop. Since then, tens of millions of pounds have been invested in developing rust-resistant varieties of the grain. However, an outbreak in Uganda in 1999 was discovered to have been caused by a virulent mutation of the fungus. There has been alarm at the speed at which further mutations have subsequently developed and spread across continents.
Plant scientists in Britain estimate the latest developments mean that 90 per cent of all current African wheat varieties are now vulnerable to the disease.
Last year, Germany witnessed its first outbreak of stem rust in more than 50 years. The outbreak was spurred by “a period of unusually high temperatures and an unusually late development of the wheat crop due to cold spring and early summer temperatures”, explained Kerstin Flath, of Germany’s Federal Research Centre for Cultivated Plants.
A further outbreak occurred in Ethiopia last November, with farmers losing on average 50 per cent of their wheat crop; the worst affected lost up to 70 per cent. Experts met in Mexico last month to discuss the threat. Work is under way to examine the different strains, to identify similarities.
According to Dr David Hodson, of the International Maize and Wheat Improvement Center in Addis Ababa, the disease’s threat lies in its ability to cause “large- scale destruction in a very short period of time over very large cultivated areas”. Rust epidemics could be compared to a forest fire, Dr Hodson said. Once it manages to gain ground it can very quickly spread out of control. The fungus reproduces millions of wind-borne spores, each of which is capable of starting a new infection.
Fazil Dusunceli, of the UN’s Food and Agriculture Organisation, said that the fungal disease, along with drought, are major challenges to wheat production globally.
He warned that countries need to react quickly to counter the new fungal varieties: “Production of new seed varieties is critical.” He said the UN was looking to countries such as the US, Britain and other European nations to lead the fight. “Developed countries have well-established institutions, programmes and capacities that developing countries lack. The developing countries are not sufficiently prepared to fight against these diseases and so when epidemics occur they encounter significant losses,” he said.
British scientists from the Sainsbury Laboratory, together with those from the world-renowned John Innes centre, both in Norwich are in the vanguard of efforts to combat the outbreaks. The UK teams are trying to control the disease with genetics rather than develop more powerful chemical fungicides. The work currently includes cloning new sources of resistance from wild grasses and from barley, which they think is essentially completely resistant to wheat rust.
Academics at Cambridge University, led by Professor Christopher Gilligan, are using sophisticated mathematical models to help predict the likely spread from outbreaks. “The project is designed to develop and test mathematical models that can be used to improve understanding of when, where and how disease spreads, which regions are most at risk and how to control epidemics,” Professor Gilligan said.
Using models from the UK Meterological Office, the Cambridge team were able to predict the likely spread of the Ethiopian outbreak. “The results helped to direct sampling teams to find further outbreaks, from which it became apparent the epidemic was more severe and widespread than had been previously reported.” Further work by the modellers has identified which of the countries surrounding Ethiopia in Africa, and the Middle East, are most at risk. “The current evidence suggests that the risk of direct spread to the Indian subcontinent is small during the winter months,” Professor Gilligan said.
“The models show, however, that the fungus could spread in stages, by first infecting wheat crops in the Middle East and then spreading to other major wheat-growing areas.”
According to scientists, climate change is in part behind the threat. The aggressive spread of two forms of the fungus is widely believed to be linked to its rapid adaptation to warmer conditions. Dr Hodson said this is resulting in outbreaks in countries not previously affected, with epidemics in several countries from North Africa to South Asia. More