Photo credit: CIMMYT

Stem rust is a potentially devastating fungal disease that can kill wheat plants and small grain cereals, but more typically reduces foliage, root growth, and grain yields. The pathogen multiplies rapidly, and its spores can be dispersed by wind over thousands of kilometers.

After years of success in keeping the disease at bay, new virulent races (collectively referred to as “Ug99”) have emerged. These new variants of the disease were first found in Uganda in 1999, and have since spread to Kenya, Ethiopia, South Africa and elsewhere. These new races of rust have the potential to infect much of the world’s wheat.

The race is now on to identify resistance genes, introduce those genes into locally adapted wheat varieties, and get those new varieties into the hands of farmers to avert further losses from this disease.

Science has released the results of a global stem rust assessment study undertaken by HarvestChoice-CSIRO to

  • Model and map the global climate suitability for wheat stem rust (Puccinia graminis)
  • Conduct a spatially-explicit probabilistic assessment of the global losses attributable to the disease, and
  • Estimate the economically justifiable investment in research (and other intervention strategies) to avert losses from the disease worldwide.

The study found large geographical differences in the occurrence and persistence of the disease. The estimated total global losses in wheat production absent stem rust resistant wheat would have averaged 6.2 MT (or US $1.12 billion per year) per year from annual production of 470 MT. Eliminating such an annual loss would save enough wheat to almost satisfy the entire annual calorie deficit of Sub-Saharan Africa’s undernourished population.

Photo credit: Njoro, KenjaThese new, probabilistic loss estimates are sizable for the effects of just one disease on a staple food crop—equivalent to losing the world’s present wheat crop every 100 years. However, these losses are about one tenth of previously published estimates, which failed to account for variability of disease-induced crop losses over space and time.

The study concludes that “[m]aintaining yield growth rates necessary to meet anticipated future demands will require a sustained effort to develop wheat varieties that are resistant to contemporary races of rust. This requires an investment strategy that supports sustained research programs geared to identifying and addressing ever evolving stem rust threats.”

The study authors estimate that an investment of $51 million per year in rust resistance research is economically justified—a seemingly paltry amount but around double the annual average investment that has been made in stem rust research worldwide for the past several decades.

Failing to increase and sustain investments in rust-resistance research is tantamount to accepting an increase in the risk of yield losses on one of the world’s food staples.

Study Details
The stem rust study was undertaken by HarvestChoice-CSIRO in collaboration with colleagues from CIMMYT, the Universities of Sydney and Queensland and the Stakman-Borlaug Cereal Rust Center at the University of Minnesota.

Complete technical details and data sources developed by and used in the loss assessment study are available at
Beddow, J.M, T.M Hurley, D.J. Kriticos and P.G. Pardey. Measuring the Global Occurrence and Probabilistic Consequences of Wheat Stem Rust, HarvestChoice Technical Note, St. Paul: University of Minnesota, 2013.

Details of the modeling and global mapping of stem rust occurrence and persistence are presented in
Chai, Y., J. Beddow, R.W. Sutherst, E. Duvillier and D. Kriticos “Wheat Stem Rust.” HarvestChoice Pest Geography, St. Paul and Canberra: University of Minnesota and Commonwealth Scientific and Industrial Research Organisation, 2013 (in process).


HarvestChoice, 2013. "Right-Sizing Stem Rust Research." International Food Policy Research Institute, Washington, DC., and University of Minnesota, St. Paul, MN. Available online at

Apr 12, 2013