Emerging strains of stem rust disease of wheat, such as Ug99, are spreading out of East Africa and threatening the world's wheat supply. But the fight against this disease received a boost this week from a collaboration between the UK's Department for International Development (DFID) and the Bill & Melinda Gates Foundation. The organisations have combined to fund Cornell University with US$40 million (£25 million) to continue its work to develop wheat varieties that are resistant to the new rust strains.
The Ug99 strain of rust was discovered in Uganda in February 1999 (Pretorius et al., 2000). Before that, scientists had made great strides in combating stem rust using multi-genic resistance. With the introduction of major resistant gene Sr31 and a number of other minor genes, stem rust became less of a problem to world agriculture. But now it is back with renewed virulence, and Nature reported on 28 February that in Kenya last year, Ug99 destroyed around 80% of the wheat crop. Spores have also spread to Ethiopia, Sudan, Yemen and Iran. Scientists fear the other major wheat-growing regions of the world, including North America and South Asia, will be next.
"[Stem rust] is the source of the great biblical plague," says Ronnie Coffman, principal investigator of the Durable Rust Resistance in Wheat (DRRW) project at Cornell University.
DRRW, led by Cornell, involves 18 universities and research institutes around the world including national research centres in Ethiopia and Kenya, the Mexico-based International Maize and Wheat Improvement Centre, the International Centre for Agricultural Research in Dry Areas in Syria and the UN Food and Agriculture Organization (FAO).
It also collaborates with scientists and farmers in 40 countries where new stem rust resistant varieties have been distributed for testing and evaluation.
Andrew Bennett, president of the Tropical Agricultural Association, told SciDev.Net: "There is a need to move very quickly. Rusts like Ug99 mutate fast and are carried on the wind. Ug99 has already arrived in Iran and it is not a great distance to get to Pakistan and India, the bread basket of South Asia. It is very important that resistant material is not only developed but deployed."
As crop diseases tend to evolve rapidly, there is a need for a broad range of rust-resistant wheat varieties. While some varieties resistant to Ug99 have been developed, "We are concerned that this resistance will be overcome in a fairly short time," says Coffman. "Sometimes it lasts longer than the others."
Scientists and policymakers "must make sure they don't end up with a dominant variety or one strain, which would accelerate the development of resistance" says George Rothschild, chair of the European Forum for Agricultural Research for Development (EFARD), on SciDev.Net.
"Getting resistant crops out there is very important but in doing that it is vital that farmers do not give up their traditional varieties. The traditional varieties can be used as [the] basis to cross-breed using the resistant genes to get the anti-rust properties in," Rothschild said.
The rapid emergence and spread of new pathogen strains like Ug99 highlights the need for information gathering that keeps track of pest and disease problems at the farm level – something that will be a key part of the Global Plant Clinics that CABI is rolling out in a number of new countries. CABI's Julie Flood highlighted Ug99 as a trans-boundary disease in a paper in Food Security in 2010 which also describes the role of the Global Plant Clinics in improving food security through better plant health.
Detection of virulence to wheat stem rust resistance gene Sr31 in Puccinia graminis f.sp. tritici in Uganda. Pretorius, Z. A.; Singh, R. P.; Wagoire, W. W.; Plant Disease, 2000, 84, 2, pp 203, 1 ref. [doi: 10.1094/PDIS.2000.84.2.203B]
The importance of plant health to food security. Flood, J.; Springer, Amsterdam, The Netherlands, Food Security, 2010, 2, 3, pp 215-231, 58 ref. [doi: 10.1007/s12571-010-0072-5]