Stem or black rust, caused by Puccinia graminis, has historically caused severe losses to wheat (Triticum aestivum) production worldwide. Its control for over 30 years through the use of genetic resistance in semidwarf cultivars is a remarkable success story. However, this situation also has led to decline in research and breeding for resistance in many countries. In 1999, high susceptibility of CIMMYT germplasm was noted in Uganda and an increase in stem rust incidence and severity was seen in Kenya. The causal race, commonly known as Ug99 and designated as TTKS based on the North American nomenclature, carries virulence for several genes commonly present in wheat germplasm including gene Sr31 located in the 1BL.1RS wheat-rye translocation known to be present in several leading spring and winter wheat cultivars and germplasm worldwide. Race Ug99 is now widespread in wheat growing areas of Kenya and Ethiopia and has caused susceptibility of many popular cultivars. This race is expected to migrate further to northern Africa through Arabian Peninsula and then to Middle East, West Asia and eventually to South Asia as recently happened with yellow rust. Severe losses are likely to occur because several major cultivars in the migration path are susceptible to this race. The challenge is to identify/develop suitable resistant cultivars in a relatively short time and implement appropriate strategies to replace the susceptible cultivars before rust migrates out of Eastern Africa. Although several alien genes will provide resistance to this race, the long-term strategy should focus on rebuilding the Sr2-complex (combination of slow rusting gene Sr2 with other unknown additive genes of similar nature) to achieve long-term durability once again. A Global Rust Initiative has been launched to monitor the further migration of this race, facilitate field testing in Kenya or Ethiopia of wheat cultivars and germplasm developed by wheat breeding programs worldwide, understand the genetic basis of resistance especially the durable type, and carry out targeted breeding to incorporate diverse resistance genes into key cultivars and germplasm.

Global Wheat Program

Text in English

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