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Quantitative trait loci (QTLs) for a number of agronomically important traits of perennial ryegrass (Lolium perenne L.) were identified by means of a reference molecular marker-based genetic map. Replicated phenotypic data was obtained for a number of field-assessed morphological and developmental traits as well as the winter hardiness-associated characters of winter survival and electrical conductivity. Marker-trait association analysis was performed by a number of methods, and a high degree of congruence was observed between the respective results. QTLs were detected for morphological traits such as plant height, tiller size, leaf length, leaf width, fresh weight at harvest, plant type, spikelet number per spike and spike length, as well as the developmental traits of heading date and degree of aftermath heading. A number of traits were significantly correlated, and coincident QTL locations were identified. No significant QTLs for winter survival in the field were identified. However, a QTL for electrical conductivity corresponding to frost tolerance was located close to a heading date QTL in a region that may show conserved synteny with chromosomal regions associated with both winter hardiness and flowering time variation in cereals. The QTL analysis of multiple phenotypic traits provides the basis for marker assisted selection (MAS) of important agronomic characters, allowing genetic improvement of yield, quality and adaptation in perennial ryegrass breeding. [ABSTRACT FROM AUTHOR]