The Borlaug Blog

“It was scary,” said International Maize and Wheat Improvement Center (CIMMYT) scientist David Hodson. He was referring to hectare after hectare of wheat fields prematurely killed by a disease called stem rust in the Bale region of Ethiopia in 2013-2014. Compared with yields the previous year, average yield losses were 51 percent and reached 92 percent in some fields. This was an unfortunate example that crop failure and the resulting personal and economic consequences are still a reality for many farmers around the world.

Wheat stem rust is not a new disease. In 1935, during his graduate studies at the University of Minnesota, Nobel Peace Prize Laureate Norman Borlaug witnessed a devastating stem rust epidemic in North America that resulted in more than 52 percent  yield losses statewide in Minnesota and North Dakota.

Later, Dr. Borlaug’s Green Revolution wheat varieties combined short height, high yields, and stem rust resistance. These varieties were successful in preventing major stem rust epidemics for decades, starting in the late 1960s.

Everything changed in 2004, when an unusual stem rust epidemic decimated wheat fields in a high-elevation wheat production region of Kenya. Borlaug visited the fields in January 2005 and sounded the alarm on stem rust’s return. The stem rust fungus strain that caused the Kenya epidemic, known as Ug99, is different because it is harmful to wheat varieties that were once resistant.

In 2008, Dr. Borlaug wrote an op-ed published in the New York Times. “Ug99 could reduce world wheat production by 60 million tons,” it read. “But a global crop failure of this magnitude can be avoided. Before it is too late, America must rebuild, not destroy, the collaborative systems of international agricultural research that were so effective in starting the Green Revolution.”

Clearly, Borlaug understood the importance of international collaboration in ushering in the Green Revolution. Borlaug’s call to reinvest in wheat research was met by the Bill and Melinda Gates Foundation, the United Kingdom Department for International Development, the United States Agency for International Development (USAID), and USDA’s Agricultural Research Service (USDA-ARS).  

With an enhanced capacity to address Ug99, CIMMYT wheat breeder Ravi Singh modified Borlaug’s shuttle breeding scheme to include field testing in Kenya. Unfortunately, the stem rust fungus has the shifty ability to change. In 2006, USDA-ARS scientist Yue Jin confirmed that Ug99 had adapted to become even more virulent in Kenya. This change was in response to a Kenyan wheat variety previously resistant to Ug99. The variant of Ug99 was now even more dangerous – essentially all of the spring wheat varieties grown in the Great Plains of North America were now susceptible.

Similarly, it was a Ug99-resistant wheat variety named ‘Digalu’ that succumbed to the stem rust epidemic in 2013-2014 witnessed by David Hodson. The cause of the epidemic was actually not Ug99 or a variant of Ug99, but a completely different form of the stem rust fungus. This epidemic highlighted the need for wheat varieties with resistance not only to Ug99, but also to other strains of the stem rust fungus.

Starting in 2014, I led a team composed of scientists at the Ethiopian Institute of Agricultural Research (EIAR), CIMMYT, and the USDA-ARS to establish new screening sites in Ethiopia where wheat lines could be evaluated against Ug99 and the other virulent strains of the stem rust fungus. Excellent collaborators including Bedada Girma (EIAR), Bekele Hundie (EIAR), Bekele Abeyo (CIMMYT), Ayele Badebo (CIMMYT), Pablo Olivera (University of Minnesota), and Gordon Cisar (Cornell University) worked to implement these nurseries and obtain field data as quickly as October 2014. The information validated that the Kenyan variety ‘Kingbird’ was resistant to the multiple strains. Work by EIAR, CIMMYT (Sridhar Bhavani), and Cornell facilitated the release of ‘Kingbird’ in Ethiopia in 2015.

Stem rust screening in Africa also informed U.S. wheat breeders. The USDA-ARS prioritized the screening of United States germplasm in Kenya and Ethiopia since 2005 in collaboration with CIMMYT, EIAR, and the Kenyan Agriculture and Livestock Research Organization.

In 2013, the University of Minnesota released a variety named ‘Linkert’ that possessed resistance to Ug99. Wheat breeder Jim Anderson had selected Linkert to advance as a variety because of its competitive yield, baking quality, straw strength, and resistance to Ug99. Since 2016, Linkert has been the most widely grown wheat variety in Minnesota and is also widely grown in eastern North Dakota. The cultivation of a Ug99 resistant variety in the region of the United States historically most vulnerable to stem rust significantly protects the spring wheat crop from the threat of Ug99.

In the tradition of Dr. Borlaug, an international team of scientists came together, equipped with necessary resources, to address and mitigate a significant threat to global wheat production. The work fit with USDA Secretary of Agriculture Sonny Perdue’s motto “do right and feed everyone” – at national and international levels. Going forward, we must continue our collaborations and not grow complacent. We must continue to work together and build on Borlaug’s “collaborative systems of international agricultural research” to keep the world’s food supply secure.