A group of plant viruses that infect many important crops may have origins stretching back tens of thousands of years, long before humans began farming.
A new international study suggests that the ancestors of modern tymoviruses likely appeared before the last Ice Age, revealing that some crop diseases have far deeper evolutionary roots than scientists once thought.
The research, published in the journal Plant Disease, examined the history of tymoviruses, a group of viruses known to infect a wide range of plants.
These viruses mainly attack dicot plants, which include many vegetables, legumes, and oilseed crops. They are often spread by leaf-eating beetles, but they can also pass from plant to plant through seeds or direct contact.
Tymoviruses are found across Eurasia and the Americas and infect both wild plants and agricultural crops.
In farming systems, they can cause serious diseases in important crops such as cabbage, broccoli, and other brassica vegetables.
They also affect plants in the nightshade family, including potatoes, tomatoes, tobacco, and eggplants. In other regions, tymoviruses infect legumes grown in parts of Africa, Southeast Asia, and Australia.
To better understand where these viruses came from, an international team of researchers led by Adrian J. Gibbs from the Australian National University analyzed the genetic material of 109 different tymoviruses.
By studying their genomes and comparing how closely related they are, the scientists reconstructed the viruses’ evolutionary history.
Much of the genetic material used in the study came from historical virus collections that scientists have preserved over many decades.
By combining these older samples with modern genetic analysis, the team was able to estimate when different virus lineages first appeared and how they spread over time.
The results suggest that the most recent common ancestor of all known tymoviruses existed before the last Ice Age, which ended roughly 11,700 years ago. Some virus lineages may have reached the Americas about 15,000 years ago, possibly carried by wild plants or insect vectors as ecosystems shifted during that time.
Interestingly, the study also found that most tymoviruses now found on multiple continents appear to have spread globally much more recently.
Many of these movements likely occurred within the past two hundred years, a period when international trade and agricultural exchange expanded rapidly.
The research also uncovered clues about how these viruses evolve. Some parts of the viral genome, especially those responsible for replication and forming protective structures, appear to change very slowly.
These genes are under strong evolutionary pressure to remain stable. Other genes, particularly those that help the virus move between plant cells, evolve much faster. This flexibility may allow the viruses to adapt to new plant species, including crops grown by humans.
The project itself represents a collaboration across countries and generations of scientists. Researchers from South America, Europe, the Middle East, and Australasia contributed to the work. Notably, lead author Adrian J. Gibbs published one of the first studies describing an Andean tymovirus nearly sixty years ago, in 1966.
Understanding the deep history of plant viruses is important today because global agriculture is increasingly interconnected. Seeds, plants, and food products move around the world more quickly than ever before.
By learning how viruses evolved and spread in the past, scientists can better predict future disease risks and help protect crops and ecosystems from emerging plant infections.
Source: KSR.
