About 50 percent of the world's wheat is grown in developing countries where it serves as a staple food source for most subsistence farmers. Wheat is subject to a variety of diseases, including rusts.
In 1999, what is now known as Ug99 was found on wheat in Uganda that was bred to be resistant to stem rusts. A particular gene, Sr31, was responsible for keeping the wheat stem rust-free. Sr31 worked, keeping wheat around the world free of stem rust until Ug99 came on the scene. Ug99 was observed in 2001 in Kenya and 2003 in Ethiopia. The fungus has since spread farther south in Africa, to the Middle East and South-east Asia, and could spread throughout the world.
"The likelihood that it would blow across the Atlantic is low because crops on the two sides of the Atlantic are different; however, if introduced to North America, the majority of our wheat varieties would be susceptible," said Marty Draper, National Program Leader - Plant Pathology with the U.S. Department of Agriculture/National Institute of Food and Agriculture. "There is still a great concern that it could be introduced by travelers and agri-tourists."
Like other cereal rusts, Ug99 infects the above-ground part of the wheat. What is unique to stem rust is that stems can also be infected, which increases the chances of lodging (or falling down), which will increase yield loss. The lost yield is from fewer and lighter seeds. Crop yields can be reduced by 50-100 percent and in some cases, the rust will kill the plant prematurely.
"It would be an extreme case to see localized starvation as a result of Ug99," Draper said. "More likely, there will be emigration and malnutrition. The potential outcomes are pretty severe."
There are two ways to deal with Ug99. Farmers can use a fungicide to protect the plant from infection or grow new rust-resistant wheat cultivars. Since fungicides can be too expensive for many of the small-scale farmers grappling with Ug99 in the developing countries of Africa and the Middle East, a new cultivar seems to be the only option, MSU's Huang said.
Draper agreed that, "Resistant varieties, when available, are generally the least costly and most effective option for plant disease control."
Very few varieties of wheat are resistant to Ug99, so breeders are looking for new sources of resistance genes from species that are closely related to wheat or even rice, Huang said. However, not all resistance genes from other species can function as expected in wheat because of suppressor genes residing in the wheat genome.
In Huang's new project she will investigate two suppressors of rust resistance in wheat. When these suppressor genes are inactive, the plant is resistant to Ug99. When the suppressor genes are active, they smother the beneficial effects of the resistance genes and the plant is vulnerable to Ug99.
Once the two suppressors are characterized, Huang's team will replace the active suppressors with the inactivated suppressor genes, into wheat breeding programs in Kenya, where they currently have problems with Ug99.
"While this work is specific to Ug99, it has broader implications for any kind of rust," said Huang. "Rust is a very ancient disease. Farmers saw it as early as 500-800 B.C., but they didn't know the cause; they thought it was a punishment from the gods."
The project will unlock an extensive array of rust resistance genes in the wheat genome. The project will also reveal how the suppressors regulate the defense response and provide knowledge for effectively using genes from other species.
Training of young scientists is equally important in this project. Exchange programs and videos will train scientists from Kenya and China during the grant and build the basics for long-term improvement of agricultural output.
The BREAD program supports basic research for generating sustainable, science-based solutions to agricultural problems in developing countries. The five-year program is jointly funded with the Bill & Melinda Gates Foundation and aims to help small farmers in the developing world grow more and earn more so they can lift themselves and their families out of hunger and poverty.
Li Huang at 406-994-5058 or firstname.lastname@example.org