Genge, who had been named as a replacement, has suffered a foot injury and Obano will take his place on the bench in the game at Rome's Stadio Olimpico.
You can see the full team news for England below:
Ellis Genge ruled out of England team to face Italy in Rome
Prop Ellis Genge has been ruled out of the England team for their Six Nations opening match against Italy and will be replaced by Beno Obano.