RNA sequencing of 750-year-old barley virus sheds new light on the Crusades

Researchers at the University of Warwick have detected and sequenced the RNA genome of Barley Stripe Mosaic Virus (BSMV) in a 750-year-old barley grain found at a site near the River Nile in modern-day Egypt.

This new find challenges current beliefs about the age of the BSMV virus, which was first discovered in 1950 with the earliest record of symptoms just 100 years ago.

Although ancient DNA genomes have been sequenced before, ancient RNA genomes have not been as RNA breaks down more rapidly than DNA – generally around 50 times as fast. However in extremely dry conditions, such as those at the site in Qasr Ibrim in Lower Nubia where the barley was found, RNA can be better preserved and this has allowed the scientists to successfully sequence its genome.

Using the new medieval RNA to calibrate estimates of the rate of mutations, the researchers were able to trace the evolution of the Barley Stripe Mosaic Virus to a probable origin of around 2,000 years ago, but potentially much further back to the domestication of barley in the Near East around 11,000 years ago.

The researchers believe that the Medieval BSMV genome came from a time of rapid expansion of the plant disease in the Near East and Europe. This coincided with the tumult of the Crusades which saw the Christian lands of Europe take arms against the Muslim territories of the Near East with their sights set on the city of Jerusalem. The seventh Crusade of Louis IX in 1234 is the most closely aligned in date to the origin of the virus expansion.

The researchers believe the massive war effort could have caused the virus to spread, fuelled by an intensification of farming in order to feed the armies engaged in the campaign.