Patterns of Variation in a Collection of Timothy Accessions

Cultivated timothy ( Phleum pratense L.) is an important grass for hay production in temperate North America. It is under utilized in management‐intensive rotational grazing systems because of its poor persistence when frequently defoliated. The objective of this study was to evaluate the USDA‐NPGS collection of timothy accessions for agronomic traits, including persistence under frequent defoliation. Unlike previous reports for infrequent harvest systems, diploid and tetraploid species of Phleum were similar in forage yield to hexaploid P. pratense , suggesting their potential value in livestock agriculture. Cultivated accessions tended to have fewer, but larger leaves; longer and narrower panicles with a greater number of smaller seeds; lower survival under frequent defoliation; and higher forage yield than natural accessions. A considerable amount of phenotypic variation among accessions was explained by geographic source of the accessions. Twenty‐one unique phenotypic clusters were formed to account for 50% of the phenotypic variability among accessions, providing the basis for development of a core collection for P. pratense Clusters were highly differentiated on the basis of geographic origin of the accessions, underscoring the potential importance of the relationship between phenotype and geography in hexaploid timothy.