The National Turfgrass Evaluation Program (NTEP) conducts trials throughout the United States on turfgrass adaptation. This trial was established in September 2010 as a part of the NTEP program. It contains 88 perennial ryegrass cultivars.
Iowa State University
Christians, Nick E. and Jones, Marcus, "Perennial Ryegrass Study" (2012). Iowa State Research Farm Progress Reports. 36.