GENETIC-VARIABILITY OF FAGUS-SYLVATICA L IN ITALY - THE ROLE OF POSTGLACIAL RECOLONIZATION

Genetic variability of 21 Italian populations of beech (Fagus sylvatic a L.) was studied using starch gel electrophoresis and nine polymorphi c enzyme gene loci. Expected mean heterozygosity varied from 13.6 per cent to 20.3 per cent. Observed heterozygosity was less than expected in all but two populations. No association between allele frequencies and soil type or altitude was found. As in other forest tree species, the among-populations component of variability was low (average F-ST=0 .046). Despite low genetic differentiation, principal components analy sis of allelic frequencies revealed a geographical pattern. The first principal component, significantly correlated with latitude and longit ude, showed a clear separation of southern and northern populations. T he statistical significance of the geographical pattern was tested by a resampling technique (bootstrap). The origin of Italian beech popula tions from eastern and southern refugia during the last glaciation is discussed. First principal component values and the higher allele vari ability found in southern populations seem to concord with the palynol ogical evidence for a southern origin of beech in the peninsular part of Italy.