Developing new soybean lines against destructive red leaf blotch disease

Amy Karagiannakis
College of ACES, University of Illinois
Glen Hartman, right, pictured with Pan-African Soybean Variety Trial collaborators with the International Institute of Tropical Agriculture (IITA) at a field site in Zambia in March 2019.

URBANA, Ill. – A little known fungus in Africa has the potential to wreak havoc on the soybean crop around the world.

Listed as No. 61 on the the Select Agent and Toxin list established by the Federal Select Agent Program (FSAP) is the fungus Coniothyrium glycines, the cause of a soybean disease referred to as red leaf blotch (RLB).

The FSAP was launched following the anthrax attacks in 2001 as a means to regulate the possession, use and transfer of select biological agents and toxins that could pose a severe threat to public, animal or plant health.

RLB which has caused nearly 70% losses of soybean production in Africa, is a genuine biological threat to to soybean crops in the U.S. Currently the U.S. is the world's leading producer of soybeans and the second-leading exporter. 

While Red Leaf Blotch is currently found in Africa, spread of the disease could pose a major potential threat to soybean production.

The spread of the disease could impact the global economy and further devastate the American soybean farmer, according to researchers in the USAID Soybean Innovation Laboratory (SIL), housed in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois.

RLB is native to Africa and currently affects soybean in central and southern Africa. Sub-Saharan African countries have reported soybean production losses of up to 70% due to RLB. The first cases of RLB were reported in Ethiopia in 1957; yet, very little is known about the fungus today.

While the U.S. and Brazil recognize RLB as a major potential threat to soybean production, research on how to combat the fungus is limited.

The pod on this soybean plant is infected with Red Leaf Blotch.

“Just like disease-causing pathogens of humans, there are disease-causing pathogens of soybean. One of these diseases is red leaf blotch, which occurs in Africa. The disease is important because it reduces soybean yields where it is endemic to some locations in Africa,” says Glen Hartman, a crop scientist in the College of ACES at U of I.

Hartman serves as plant pathologist for USDA Agricultural Research Service (ARS) and collaborates with SIL on researching RLB. He says that finding resistance in other exotic lines could provide soybean breeders with germplasm to develop resistant cultivars. However, there has been little progress made on discovering sources of resistance to the fungus that causes RLB.

 “Our research through SIL focuses on developing disease management techniques to control red leaf blotch that would be useful to African soybean producers, as well as U.S. soybean producers,” Hartman says. 

Hartman received funding from USDA-ARS to evaluate soybean genotypes for resistance to RLB. However, because C. glycines is on the Select Agents and Toxins list, it is nearly impossible to conduct research on the disease in the U.S. SIL manages 72 field sites across 14 countries in West, East and Southern Africa through the Pan-African Soybean Variety Trial (PAT) program, many of which have reported cases of RLB.

Harun Murithi, second from left,  training Soybean Innovation Lab trial operators on how to identify and assess soybean diseases like red leaf blotch. This training took place at a Pan-African Soybean Variety Trial site in Nyankpala, Ghana, in October 2019.

Post-doctoral fellow and SIL research partner Harun Murithi, who collaborated with Hartman to develop SIL’s Field Guide to African Soybean Diseases and Pests, will be conducting on-site research at SIL’s PAT sites in Ethiopia, Malawi, Tanzania, Rwanda, Uganda, and Zambia. Hartman and Murithi will evaluate the severity of RLB at several of these sites.

Hartman explains that seeds of the best genotypes will be retested at the Foreign Disease-Weed Science Research Unit (FDWSRU) at Fort Detrick, Maryland. Once the analyses confirm resistance, results will be disseminated through SIL’s global network of soybean breeders. Breeders in the U.S., as well as Africa, can then use these sources of resistance to make crosses and develop soybean populations with resistance to RLB.

“While red leaf blotch has not yet been reported outside of Africa, the potential threat exists, making it critically important to prepare for the possibility that American soybean crops could be exposed to the fungus that causes RLB, whether intentionally or unintentionally,” Hartman concludes. “Developing soybean lines with resistance to RLB will not only lead to improved soybean production across sub-Saharan Africa, but will also prevent potentially disastrous effects on the U.S. soybean crop.”