PATTERNS OF GENETIC DIFFERENTIATION IN 2 ANNUAL BROMEGRASSES, BROMUS-LANCEOLATUS AND BROMUS-HORDEACEUS (POACEAE)

Infraspecific genetic differentiation was analysed in two tetraploid a nnual bromegrasses, Bromus lanceolatus (from N Africa) and B. hordeace us (from N Africa and France). Genetic analysis of populations was bas ed on allozyme polymorphisms at 17 loci. Different fixed heterozygous phenotypes were scored in both species, according to their allopolyplo id origin. In N Africa, more variation occurred among populations of B . lanceolatus than of B. hordeaceus. The variation was not randomly di stributed among populations of both species. In B. lanceolatus, differ entiation was correlated with climatic variables rather than with geog raphic distance between populations. Higher correlation of genetic dif ferentiation with geographic distance occurred in B. hordeaceus, parti cularly at large geographic scale, between French and N African popula tions. Within each region, the populations appeared weakly genetically differentiated, even when belonging to different subspecies.