Abstract

The genetic structure of the alcohol dehydrogenase (ADH) enzyme complex was studied by means of isozyme analysis among several common ash (Fraxinus excelsior L.) provenances. We analysed if specific alloforms of locus ADH-B are selected under flooding stress caused by oxygen deprivation, since ADH is a fundamental enzyme of the plant metabolism under anoxia. This selection, if given, could therefore result in different ash ecotypes. Furthermore, genetic structures in the same provenances resulting from the analysis of four nuclear microsatellite markers are also discussed and compared with those resulting from the isozyme analyses to differentiate between adaptation and demographical processes. We found the highest value of genetic diversity at one of the two examined floodplains but did not find significant correlations between genotypes structures and flooding. The observed allele distributions can be mainly attributed to high human pressure and important seed transport events. These are regarded as the main forces shaping the actual genotype distributions rather than selection processes acting on locus ADH-B.