Mutation may be Responsible for Disease Resistance in Cassava

Article by: Hari Yellina

ETH Zurich, University of California Los Angeles, and the National Crops Resources Research Institute (NaCRRI) in Uganda have joined forces with Rebecca Bart, PhD, associate member, and Nigel Taylor, PhD, associate member, and Dorothy King distinguished investigator, Donald Danforth Plant Science Center, to conduct ground-breaking research that has identified a genetic mutation that confers resistance to cassava mosaic disease (CMD). Their research has important ramifications for increasing cassava productivity and protecting farmer income in the face of a widespread disease. Additionally, their discovery may provide insight into other important crops’ disease resistance. Recent publication in the academic journal Nature Communications of this landmark study, Mutations in DNA polymerase subunit 1 co-segregate with CMD2-type resistance to cassava mosaic geminiviruses.

Farmers in several of the world’s greatest cassava-producing regions, including Southeast Asia, Africa, and India, all too frequently experience significant yield losses as a result of CMD. Stunted and underdeveloped storage roots that are used for feeding characterise CMD-infected plants. The current study into the genetic basis for resilience to the virus was inspired by Taylor’s team’s unanticipated discovery of plants in the field that had lost resistance to CMD several years ago. We might not have pursued this experiment, says Bart, if CMD-resistance hadn’t magically vanished. The scientists realised right away that they had made a significant discovery. The Danforth team launched tests to identify the genetic basis for CMD resistance with the help of the Institute for International Crop Improvement at the Danforth Center. The partnership expanded to involve collaborators from NaCRRI, UCLA, and ETH-Zurich, and it received further financing from the Bill & Melinda Gates Foundation.

Their discovery gives light on how resistance was obtained and how to maintain resistance to assure yields in the future by pinpointing the precise genomic region that confers CMD-resistance, down to a single nucleotide. Furthermore, according to Bart, similar viruses “target many other crops, including cotton and tomato.” This discovery might offer methods for preventing diseases in those crops as well. For the researchers to make their discoveries, field study on cassava is essential. In Uganda, a region known as a “hotspot” for CMD, the NaCRRI team farmed cassava for two years while recording the prevalence of disease in the field. More research questions and opportunities have arisen as a result of the identification of a single mutation that confers CMD resistance. We must first understand the mechanism by which the mutation gives resistance, says Bart. Knowing how resistance works will probably help us predict how stable resistance will be in the long run. The research team will carry on its international collaboration and cassava studies while emphasising the value of concentrating research on less well-known crops.