Long before humans cultivated crops or sailed between continents, a group of plant viruses was already evolving among wild plants in Eurasia. According to a new international study published in Plant Disease, the ancestors of modern tymoviruses likely emerged before the last Ice Age, reshaping scientists' understanding of the vast evolutionary history of plant disease.
Tymoviruses infect dicot plants and are typically spread by leaf-eating beetles, although they can also be transmitted through seeds or direct plant contact. In parts of Eurasia and the Americas, these viruses infect both wild and crop plants, causing serious diseases in economically important crop plants, including several cultivated oilseed and vegetable brassica species and solanaceous crops such as potato, tomato, tobacco, and eggplant. They also infect legumes in Africa, Southeast Asia, and Australia. Because these viruses affect both cultivated plants and wild species, their spread has implications for both agriculture and natural ecosystems.
Led by Adrian J. Gibbs, Emeritus Faculty at the Australian National University, an international team of researchers conducted phylogenetic analysis and genomic sequencing of 109 tymoviruses and reconstructed their evolutionary relationships to estimate when and where this group of viruses first emerged. The newly sequenced tymovirus isolates mostly came from historical virus culture collections. The results suggest that the most recent common ancestor of all known tymoviruses existed before the last Ice Age, with some viral lineages likely reaching the Americas approximately 15,000 years ago. In contrast, the few tymoviruses that are now found on more than one continent appear to have spread globally much more recently—primarily during the past two centuries, coinciding with the expansion of international trade and agricultural exchange.
The analysis also revealed important clues about how these viruses adapt over time. Genes responsible for viral replication and protective structure showed strong evidence of stabilizing evolutionary pressure, while the genes responsible for movement between plant cells appear to evolve more rapidly. This flexibility may help the viruses adapt to new plant hosts, including economically significant crops.
Beyond the scientific findings, the study represents an important collaboration across both geography and generations. The research team includes scientists from South America, Europe, the Middle East, and Australasia, combining expertise in modern genomic sequencing and virus population genetics with decades of historical research on plant viruses. The study's lead author, Adrian J. Gibbs, published one of the earliest studies describing an Andean tymovirus in 1966, while other contributors have worked on Andean potato viruses since the 1970s.
Understanding how these viruses originated and spread helps researchers anticipate future risks in a world in which plants, seeds, and agricultural products move between continents faster than ever before. The study shows that while the evolutionary roots of some crop viruses stretch back to a world shaped by glaciers and prehistoric ecosystems, human activity in recent centuries has played a major role in shaping their modern distribution. This broader perspective provides valuable information for scientists studying virus evolution and for plant health and biosecurity authorities responsible for protecting crops and ecosystems from emerging diseases.
Read " A Phylogeny of the Tymoviruses, Sensu Stricto, and Its Global Interpretation in Space and Time " to learn more—published in Plant Disease.
Plant Disease, published by The American Phytopathological Society, is the leading international journal for rapid reporting of research on new, emerging, and established plant diseases. The journal publishes papers that describe translational and applied research focusing on practical aspects of disease diagnosis, development, and management in agricultural and horticultural crops.
