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Stem rust:Chemical control of stem rust
In Europe systemic, broad-spectrum fungicides are used routinely in commercial fields (hence breeding for stem rust resistance is not considered a high priority).[Singh et al., 2011] In LEDCs this is often not an option due to either cost or unavailability of fungicides.

Sr genes
A number of stem rust resistance genes (Sr genes) have been identified in wheat. Some of them arose in bread wheat (e.g. Sr5 and Sr6), while others have been bred in from other wheat species (e.g. Sr21 from T. monococcum) or from other members of the tribe Triticeae (e.g. Sr31 from rye and Sr44 from Thinopyrum intermedium).

None of the Sr genes provide resistance to all races of stem rust. For instance many of them are ineffective against the Ug99 lineage. Notably Ug99 has virulence against Sr31, which was effective against all previous stem rust races.

Singh et al., [2011] provide a list of known Sr genes and their effectiveness against Ug99.

Location and predicted spread

 * Mention possibility of an epidemic.
 * Mention 'mega-cultivars' in India and Pakistan.
 * Wind movements.
 * Areas of wheat production.
 * Susceptibility.

Races
There are seven races of Ug99, which (under the North American nomenclature system) have the designations TTKSK, TTKSF, TTKST, TTTSK, TTKSP, PTKSK and PTKST. They are all closely related and are believed to have evolved from a common ancestor.

TTKSK was the first Ug99 race to be characterised. Like most Ug99 races, and unlike other stem rust varieties, it is virulent against the Sr gene Sr31. It is known to be present in Uganda, Kenya, Ethiopia, Sudan, Yemen, Iran and Tanzania.

TTKST, discovered in Kenya in 2006 was the first Ug99 race found to be virulent against the Sr gene Sr24.

A table of the seven currently known Ug99 races, along with their virulences and the countries in which they have been confirmed can be found in Singh et al., 2011.

Mitigation of Ug99

 * Current resistant strains. (The problems associated with release of resistant strains containing genes that are going to be combined).
 * Chemical control.
 * In Europe systemic, broad-spectrum fungicides are used routinely in commercial fields (hence breeding for stem rust resistance is not considered a high priority). In LEDCs this is often not an option due to either cost or unavailability of fungicides.


 * Plan for the future:
 * Combine race-specific Sr genes.
 * Durable adult plant resistance.
 * Other solutions? See Collinge et al.