‘JS501’ and ‘Replay’ perennial ryegrass (Lolium perenne L.) were developed from a serendipitous discovery of natural glyphosate resistance in an aging turf trial. Both JS501 and Replay are turf-type diploid (2n=2x=14) cultivars developed by Jacklin Seed by Simplot® in a conventional population improvement program and released in 2010.  In 1999, at the termination of a 1996 turf trial in Maryland, 96-3047 was the only plot in the trial not killed when glyphosate was applied at the rate of 1.7 kg ae/ha.  Survival in the plot was estimated at 30% and samples were pulled.  Several cycles of development followed to make the cultivars homozygous and stable for the glyphosate trait and improve turf characteristics.  Glyphosate tolerance with minimal discoloration of JS501 is 0.42 kg ae/ha and 0.53 kg ae/ha for Replay.  Seed production fields of JS501 and Replay are routinely sprayed at the 0.42 kg ae/ha rate.

During development glyphosate tolerance was not observed to spread to any additional germplasm in surrounding perennial ryegrass nurseries.  Over 3 years of commercial seed production, glyphosate tolerance has not been found in cultivars planted in adjacent production fields when sampled and treated with glyphosate.

Glyphosate’s mode of action is to inhibit the EPSPS enzyme which is important in the shikimate pathway.  The glyphosate tolerance of JS501 and Replay is associated with two nucleotide mutations of the EPSPS gene at position 25, adenine to guanine; and at position 274, cytosine to thymine.  These mutations result in two amino acid changes in their encoded EPSPS protein.

These varieties were developed for use as improved turfgrass in permanent turf or for winter overseeding of dormant bermudagrass in areas where Poa annua L. is a competitive weed.  The glyphosate tolerance of JS501 and Replay allow their use in renovation projects as a step in eradicating Poa annua.