Examining perennial ryegrass (Lolium perenne L.) persistence through comparative genetic analyses of two cultivars after nine years in the field.

Perennial ryegrass (Lolium perenne L.) is commercially important providing a cost-effective forage species for New Zealand farms. Vegetative persistence (maintained herbage growth and survival without reseeding) is an important trait for decreasing costs of pasture establishment. Breeding for vegetative persistence is difficult because of a deficiency of long-term trials to observe the complex interactions between plant genotype and environment. Over time in a long-term trial, a shift in the genetic mean of a cultivar could occur as plants with genetically enhanced persistence traits survive. This study aimed to identify a shift in the genetic mean of two cultivars sown in a long-term trial in Hawkes Bay, New Zealand. A 1m row trial was assessed for 13 months to compare changes in additive genetic variation (σa2), narrow-sense heritability (h2n), and trait associations of half-sib (HS) populations generated from Persistent plants and commercially bought seed of Original cultivars Grasslands Samson and Commando. Significant (P<0.05) σa2 and high levels of h2n for some populations were identified for scores of herbage growth, leaf width, plant habit and aftermath heading. This study found genetic shifts over time were cultivar specific. Traits that were different between Persistent and Original populations were previously associated with decreased pasture intake. Trait associations and cluster analysis identified HS families that could be used for developing enhanced persistence.