Puccinia striiformis is a yellow rust fungus that affects wheat and other grasses as its primary host, but is not considered to be a gall-causer. Uredinia make long yellow stripes down the leaves, which become chlorotic. Telia are mainly on the stem and leaf-sheaths, and are dark brown.  It can cause severe yield loss when it attacks wheat crops.

The alternate host plant is Barberry, Berberis.

There are other species of rust fungi found on grasses, cereals and Barberry

host/microscopy

Photograph the rust on the host.  Ensure you have noted the host-plant species in your comments.  Microscopic examination will be needed

The primary stage is usually associated with wheat crops although it does affect other grasses.  The alternate stage is Barberry.