An important factor in the establishment of high quality perennial ryegrass (Lolium perenne L.) turf is to start with pure seed, free of contamination from weeds and annual type grasses. We are developing predictive laboratory tests using molecular markers to determine growth habit from samples of ryegrass seed or seedlings. A genetic map of the Lolium genome was developed based upon an interspecific (L. perenne and L. multiflorum Lam.), three-generation, mapping population (MF). Construction of the MF map was facilitated by comparison with established maps of the cereal crops in the Triticeae tribe. Molecular markers that are predictive of growth habit and the control of flowering in the ryegrasses are being identified in the MF population. Lolium flowering-related genes, LpCO and LpID1, have been mapped to ryegrass linkage group (LG)7 and 5, respectively, in regions associated with vernalization-response QTLs.  LpCO belongs to a family of putative transcription factors, and is similar to the CONSTANS-like homologs ZCCT-1 and HvZCCT, identified in winter wheat and barley that play a central role in the vernalization response. LpID1 is a homolog of the gene Indeterminate, shown to control the transition to flowering in maize.  We have also identified a SNP marker in LpVrn-1 on LG4, syntenic to the region of the Triticeae chromosome 4 containing the primary vernalization response gene, Vrn-1. Gel electrophoresis-based tests for the isozymes pgi-2 and sod-1, shown to predict annual-type growth habit better than a grow-out test (GOT), are also being developed. When procedures are optimized, molecular markers will be useful as predictive tests in seed testing labs for certifying genetic purity and identity of ryegrass cultivars.