A new study reveals how war, trade, and agriculture helped a destructive rice virus spread across Africa over the past 150 years. The research, published on June 17 in PLOS Pathogens, shows that human movement and farming practices have played a major role in the long-distance spread of rice yellow mottle virus (RYMV), a major threat to African rice crops.
Led by Dr. Eugénie Hébrard of the French Institut de Recherche pour le Développement (IRD), the research traced the virus's origins and movements using genetic data from hundreds of RYMV samples collected in East Africa between 1966 and 2020.
According to the study, RYMV likely first emerged in the Eastern Arc Mountains of Tanzania around the mid-1800s, an area where rice was grown using slash-and-burn methods. The virus initially jumped from wild grasses to cultivated rice and quickly spread to other rice-growing regions nearby, including the Kilombero Valley and Morogoro.
The research also uncovered how human actions—such as transporting infected rice plants and seeds—helped the virus travel much farther. RYMV moved westward along trade routes in the late 1800s, reaching West Africa and eventually Madagascar by the late 1970s. The virus even spread during World War I, when rice supplies for troops may have carried it from Tanzania to southern Malawi.
Although RYMV is not directly transmitted through rice seeds, the study shows it can hitch a ride on contaminated plant material—making the movement of seeds and crops a key risk factor. The virus now affects rice production in multiple regions across the continent.
Researchers warn that plant viruses like RYMV, even without seed transmission, can travel across borders and continents, much like animal viruses. The findings highlight the importance of monitoring agricultural trade and seed movement to prevent further spread of crop diseases.
“This study shows how deeply human history is tied to the spread of plant diseases,” said the authors. “It also underlines the global risks posed by plant pathogens and the need for better control strategies.”
