Wheat grain samples, with 20 kernels in each, showing various levels of damage due to stem rust (Puccinia graminis), from unaffected (left), to 100% damage (right). This shows the effect of the disease in loss of yield and grain quality. The sample on the far left shows healthy, plump grain that has been protected from rust, for example by resistance or by chemical control. The progression from left to right shows increasing levels of disease. Arriving at the sample on the far right, these small and shriveled grains are very likely to be lost during threshing and have almost no flour content.
In this case the stem rust infection is by the virulent Ug99 race and the samples were taken from the ongoing screening program at the Njoro research station in Kenya. The station is part of the Kenya Agricultural Research Institute (KARI), which is working in partnership with CIMMYT to identify sources of resistance to Ug99. This strain of the disease, which emerged in Uganda in 1999, is already endemic in the area, making it possible to use Njoro as a testing ground for wheats from all over the world. More than 30,000 wheat lines are now being screened each year.
For more information on the disease, see CIMMYT’s Wheat Doctor: http://wheatdoctor.cimmyt.org/en/pests-a-diseases/list/122?task=view.
For more on CIMMYT’s ongoing work on Ug99, see the following e-news stories:
2010, “Planting for the future: New rust resistant wheat seed on its way to farmers”: http://www.cimmyt.org/newsletter/231-2010/716-planting-for-the-future-new-rust-resistant-wheat-seed-on-its-way-to-farmers.
October 2009, “From Cairo to Kabul: Rust resistant wheat seed just in time”: http://www.cimmyt.org/newsletter/38-2009/460-from-cairo-to-kabul-rust-resistant-wheat-seed-just-in-time.
December 2008, “Report from the field: Wheat stem rust resistance screening at Njoro, Kenya”: http://www.cimmyt.org/newsletter/37-2008/110-genetic-resources-program.
December 2006, “Threat level rising”: http://www.c