Isozyme polymorphism in a collection of Spanish and French perennial ryegrass populations

Abstract

Twenty-eight natural populations of perennial ryegrass (Lolium perenne L) collected from a latitudinal and a longitudinal gradient in Spain, Portugal and France were screened for allozyme diversity at ten loci. Population genetic statistics were found to be of the same magnitude as those previously reported for other outbreeding species (average number of alleles per locus = 2.82, observed heterozygosity = 0.289 and expected heterozygosity = 0.312). Genotype frequencies at most collection sites did not deviate significantly from Hardy-Weinberg expectations. Gene diversity was mainly explained by the within population component. The between population differentiation (F(ST)) averaged over seven loci was 0.073, which only accounted for 7.9% of the whole diversity. Non-metric multidimentional scaling carried out on the matrix of Cavalli chord distances, based on allelic frequencies, showed that the global differentiation between the populations was partly explained by the latitude and the altitude of the collection sites. Thus, a south-north cline was observed for ACP2-20 and PGI2-20 alleles. In the same way, more SDK1-30 and PGI2-20 alleles were found in populations from higher altitudes. Hypotheses on the origin of such clinal trends are briefly discussed.