Global Wheat Surveillance Network Takes on Stem Rust
Norman Borlaug. Image: USDA, Wikimedia
Wheat farmers in East Africa and the Middle East are on alert after a damaging strain of a plant disease called stem rust decimated more than 10,000 hectares of wheat in southern Ethiopia, the largest wheat producer in Sub-Saharan Africa (SSA), according to a report discussed at an international gathering of the world’s top wheat experts.
The details of the stem rust outbreak in Ethiopia’s Bale zone is a prominent topic at the Borlaug Global Rust Initiative (BGRI) 2014 Technical Workshop. Together with the Borlaug Summit on Wheat for Food Security from March 25-28, the BGRI is celebrating the 100th anniversary of the birth of Norman Borlaug, a legendary scientist who developed high-yielding, semi-dwarf wheat that is credited with sparking the Green Revolution and saving over one billion people from starvation.
“Dr. Borlaug taught us that rust never sleeps, which is why we now have the capabilities to detect an outbreak like the one that has occurred in Ethiopia, and to quickly mobilize a global response,” says Ronnie Coffman, professor of plant breeding and genetics at Cornell Univ., and director of the Durable Rust Resistance in Wheat (DRRW) project. He notes that the global consortiums Borlaug helped organize late in his life — now known as the Borlaug Global Rust Initiative and the DRRW project — have been key to aggressive rust intervention in Ethiopia.
Detective work by the International Maize and Wheat Improvement Center (CIMMYT), DRRW, the Ethiopian Institute of Agricultural Research (EIAR), the USDA-ARS Cereals Disease Laboratory in Minnesota and the Global Rust Reference Centre (GRRC) in Denmark have revealed that the strain of stem rust damaging wheat in Ethiopia is possibly similar to a strain found in Turkey since 2007 and in Egypt and Germany in 2013. However, the pathogen did not have a noticeable impact on production in these areas.
According to David Hodson, a senior scientist with CIMMYT’s Global Cereal Rust Monitoring Program, the previous lack of damage could mean that wheat varieties under cultivation there are resistant to an infection, there were slight differences in the strains, or that environmental conditions have not been conducive to a stem rust outbreak. Though, Hodson says wheat experts were surprised to see stem rust of any type in Germany, where the pathogen has not been detected for decades.
But during the 2013 growing season in Ethiopia, the strain was lethal to a popular variety of bread wheat called Digalu. Like other stem rusts, the disease produced brick-red blisters on the plant and caused grains to shrivel. Ironically, Digalu gained popularity in Ethiopia because it carries resistance to other strains of stem rust and to another wheat disease known as yellow or stripe rust. And these qualities have helped wheat farmers in the country produce record harvests.
“With such widespread planting of Digalu, we have not seen the major yellow rust outbreaks that were a problem in recent years and most farmers in Ethiopia have enjoyed bumper crops this season,” says Bekele Abeyo, a senior scientist and wheat breeder at CIMMYT. “But the widespread planting of Digalu may have opened the door for the incursion of a new and destructive strain of stem rust.”
Abeyo says that at the time of the stem rust outbreak in late 2013 the wheat crop was at a vulnerable stage only in the southern part of Ethiopia. Concern now turns, he says, to regions where farmers may already have begun planting for the short rainy season that runs from February/March to June/July, and are probably still using the now vulnerable Digalu variety. Wind models indicate the disease also could spread in a southwesterly direction toward Kenya, Uganda, Tanzania, Rwanda and – less probably – to countries in the Middle East. Efforts are underway to identify varieties being cultivated in these areas that might be susceptible to the strain of stem rust causing problems in Ethiopia. Officials report that a variety popular in Kenya called “Robin” is likely to be vulnerable, but, to date, there have been no confirmed reports of the Ethiopian stem rust strain in Kenya.
Bedada Girma, DRRW-Ethiopia coordinator, says working with farmers and other stakeholders to replace vulnerable varieties with resistant varieties is a high priority. But he says it will be a challenge to obtain enough seed before farmers move ahead with their next planting. Ethiopian agriculture officials also are advising farmers about how to properly use fungicides to control an outbreak.
Borlaug Legacy: a World Well-Prepared for a Mutating Pathogen
Stem rust has long been a major threat to wheat, which is a key source of calories and protein for 4.5 billion people in 100+ countries – more than half of them wheat-dependent poor who live on less than US$2 per day.
Borlaug’s signature achievement was the development and dissemination of high-yielding, stem rust-resistant semi-dwarf wheat, which helped launch the Green Revolution in farm production in Asia and Latin America. The resistance Borlaug and co-workers pioneered held up for decades, until it succumbed to a new strain of stem rust known as “Ug99,” identified in Uganda in 1999. The researchers noted that the stem rust detected in Ethiopia is not a Ug99 strain and noted that Ethiopian farmers have been aggressive in adopting new wheat varieties, like Digalu, that are resistant to both yellow rust and the Ug99 strains.
Wheat experts at the Mexico meetings note that the stem rust outbreak in Ethiopia, while a cause for concern, needs to be seen in the context of a world in which there is now a strong global network of wheat researchers capable of responding quickly to emerging threats by rapidly developing new disease-resistant varieties. In fact, Ethiopia is often cited as a model for the potential to dramatically improve wheat yields in SSA, even though production is scattered across millions of small farms that are less than one hectare in size.
According to Girma, just a few years ago, most of the wheat cultivated in Ethiopia was susceptible to either the Ug99 stem rust strains or to various strains of yellow rust. Now, most of Ethiopia’s wheat is resistant to one or both diseases. And the results can be seen in harvests that in 2004 and 2005 averaged 1.5 tons per hectare (t/ha), but now average about 2.37 t/ha. In some areas, Ethiopian farmers have even been harvesting five to eight t/ha.
“Smallholder farmers in Ethiopia are getting much better yields than they used to,” says Hodson. “That’s an incredible advance and exactly what Borlaug envisioned – that if you provide farmers in developing countries with high-yielding, disease-resistant wheat, they can begin to create the same kind of bread baskets that you see in developed countries.”
CIMMYT scientists believe many African countries are realizing only a small fraction of their wheat production potential. They are looking for ways to close the wheat yield gap and reduce the huge dependency on costly foreign imports. In 2012, CIMMYT and the International Food Policy Research Institute conducted an in-depth analysis of wheat prospects for SSA that found farmers in the region may only be growing about 10 to 25 percent of what is biologically possible and economically profitable. Such studies are attracting the attention of policy-makers, as ministers of agriculture from across Africa recently endorsed wheat as a strategic food security crop for the continent.
“The recent stem rust outbreak shows that rust preparedness is an ongoing ‘arms race.’ As pathogens evolve, new varieties must be developed,” says Coffman. “The East African highlands are hot spots for rust, but for all countries in Sub-Saharan Africa – where food security is such an issue – it is important that we continue to invest in the kinds of agricultural development partnerships bring results.”