Anyone from the team can add items to the backlog, there is no set rule for any role to add to the backlog. During the course of development, the team can find some REQUIREMENTS which were earlier not identified, they have the liberty to add that item to the backlog. SOMETIMES, the teams might IDENTIFY some stories to improve the coverage or the quality, which is a good practice to follow. Keeping this addition to the backlog OPEN for everyone in the teams ensures that we don’t miss the requirements even if it is low on the priority list. 

Though anyone in the team can add items to the backlog it is only the product owner who is responsible to prioritize the backlog and also the one who determines what happens to the product backlog item. In the grooming meeting, the team sits together with the product owner and goes through the backlog. Nowadays, the teams use online tools to help and create the backlog, this not only helps to work across the distributed teams but also helps in keeping things together. The sole intent of creating the backlog is to CAPTURE all the requirements at one place.