Genetic relationships between Lolium (Poaceae) species revealed by RAPD markers

The genus Lolium is one of the most important groupings of temperate forage grasses, including about eight recognized species that are native to some temperate and subtropical regions of the northern hemisphere. We examined genetic relationships among 18 accessions representing all Lolium species using RAPD markers. Among 50 random primers that we screened, 13 gave reproducible amplification banding patterns. Each of these 13 primers generated 19-43 scorable fragments. A total of 367 RAPD fragments were detected, of which 95.9% were polymorphic across all the Lolium accessions. Dice's coefficient of dissimilarity ranged from 0.016 to 0.622, which is indicative of substantial genetic variations in these Lolium accessions. A neighbor-joining cluster analysis, with bootstrap permutation, produced an unrooted dendrogram, which grouped 18 accessions into two main clades, supporting high bootstrap values (98 and 96%). The first clade included the self-pollinated species, L. persicum, L. temulentum, L. remotum, and L. subulatum. The cross-pollinated species, i.e., L. multiflorum, L. perenne, L. rigidum, and L. canariense, composed the second clade, in which L. canariense formed a distinct subclade, indicating its higher genetic separation from other allogamous species. The value of r = 0.97 in the Mantel test for cophenetic correlation applied to the cluster analysis indicated the high degree of fit of the accessions to a group. A principal coordinate analysis, whose first three coordinates explained 72.6% of the variation, showed similar groupings as in the cluster analysis. The genetic relationships estimated by the polymorphism of RAPD markers are basically in agreement with those previously inferred with other genetic markers.