How much differentiated are forage and turf type cultivars within L. perenne? To estimate this, we used 10 SSR/STS markers for genotyping a collection of 7 natural populations, 50 forage and turf cultivars and 4 old cultivars of dual usage registered since 1965-2004. We showed that differentiation between usage types has steadily increased since the opening of a turf national list in France and that it has mostly involved 3 markers, among which 2 were mapped onto linkage group 1 in L. perenne. Relative to natural populations, assumed to sample genetic diversity in perennial ryegrass when breeding started, turf cultivars were found to be more distantly related than forage cultivars, especially those which were recently registered. However, genetic differentiation remained primarily between cultivars whatsoever type they were. Differentiation between cultivars has increased to be about twice higher on average than between natural populations, even of quite distant geographical origin. Loss of genetic variability after 40 years of breeding was found to be very low. All alleles present in natural populations were sampled again in the collection of cultivars we investigated. The results are briefly discussed in conclusion as respect to phenotypic differentiation and efficiency of breeding methods in the grasses.
