A tensioner for a fencing wire reel, which includes a tensioning member, and a housing for the tensioning member, wherein the housing and the tensioning member are configured such that when fencing wire passes through the housing in one direction, the tensioning member applies a first biasing force against the wire, and when fencing wire passes through the housing in the opposite direction, the tensioning member applies a second biasing force against the wire, the second biasing force being less than the first biasing force. A portable fence system for constructing a fence, which includes at least one fencing wire reel, and a reel housing for the at least one fencing wire reel, and includes the tensioner as described is also claimed.
