PATTERNS OF VARIATION IN A COLLECTION OF PERENNIAL RYEGRASS ACCESSIONS

Perennial ryegrass (Lolium perenne L.) is a relatively new crop in temperate North America. Cultivars for use in this region have been introduced from temperate regions of Europe, Australia, or New Zealand. Because environmental conditions of these areas differ from those of temperate North America, currently used cultivars may not be the most appropriate for this latter region. The objectives of this study were to (i) estimate and describe quantitative genetic variation in the USDA perennial ryegrass collection, (ii) use this information to develop recommendations for future germplasm exploration, and (iii) initiate development of a core collection. Plants of 375 accessions, representing the entire collection to date, were evaluated at two Wisconsin locations for seedling vigor, leaf width, reaction to crown rust (Puccinia coronata Corda), and forage yield in 1991 and 1992. Accessions collected from cultivated sources averaged 6% greater seedling vigor, 6% wider leaves, 22% lower incidence of crown rust, and 20% higher forage yield than those from naturalized (cultivar adaptation to a local ecosystem) sources. Genotypic and phenotypic variance estimates were similar for both naturalized and cultivated groups. Thus, more than 60 yr of intensive ryegrass breeding has not greatly reduced genotypic variation among cultivated populations. Based on principal components analysis, expansion of the collection should focus an the Mediterranean Basin if the goal is to preserve natural variation, or on Eastern Europe and New Zealand if the goal is to collect germplasm with maximum forage yield for environments similar to southern and central Wisconsin. Cluster analysis was useful in identifying groups of accessions with superior performance for four traits and in classifying accessions to identify a core collection which preserved most of the phenotypic variation found within the entire collection.