RNA Sequencing of Barley Virus Sheds Light on Christian Crusades

For the first time, scientists have sequenced an ancient RNA genome - a barley virus previously believed to be only 150 years old - allowing scientists to push the virus's origin back 2,000 years. The discovery provides evidence that intense farming at the time of the Crusades contributed to its spread, according to a study published in Scientific Reports.

Researchers at the University of Warwick have sequenced the RNA genome of the barley stripe mosaic virus (BSMV), which they recovered from a 750-year-old barley grain found near the River Nile in modern-day Egypt. Extremely dry conditions at the site allowed for better preservation of the virus's RNA, which degrades much faster than DNA, usually making genome sequencing impossible.

The researchers were able to trace the evolution of the BSMV to an origin of around 2,000 years ago, possibly earlier. This estimate coincides most closely with the seventh Crusade of Louis IX in 1234.

Since BSMV is transmitted through seed-to-seed contact, it is likely to have originally been transferred from wild grass to an early cultivated form of barley while the seeds were stored. Researchers believe intensified farming used to feed the armies of Christians as they invaded Muslim territories helped to spread the virus.

Researchers said they hope understanding the origins of ancient viruses will inform present day farming practices. Robin Allaby of the School of Life Sciences at the University of Warwick, who led the study, said: "It is important to know as much as we can about virus evolution as emerging infectious plant diseases are a growing threat to global food security, and of those viruses account for almost half."

"History tells us about the devastation caused by the emergence of disease from wild hosts in disparate countries, such as the Central American origin of the oomycete that led to the Irish potato famine," Allaby continued. "We need to build up an accurate picture of the evolution of different types of virus so we can make better decisions about policies on plant movement."

In addition to the virus's origins, the study provided insights into how the virus may have moved. Genetic evidence points to a split into an east and west BSMV lineage around the end of the 15th century, around 100 years after the Mongol Empire estabilished the Silk Road. It is likely that BSMV was transported to the east via trade routes such as the Silk Road in the late Medieval period, according to the researchers.