ISOZYME STUDIES OF NEW-ZEALAND NOTHOFAGUS SPECIES (SOUTHERN BEECH) USING LEAF EXTRACTS

Leaf extracts of the New Zealand species of Nothofagus (southern beech ) were subjected to horizontal starch gel electrophoresis and stained gel slices were scored for 12 enzyme systems segregating into 22 putat ive loci. Results of isozyme analysis are supportive of the present ta xonomic concept and reveal a major genetic divergence between N. menzi esii and the remaining four species which belong to the 'fusca' group and form natural hybrids among each other. Genetic variation in N. men ziesii is distinctly higher than in any of the 'fusca' group species w here N. fusca shows the lowest levels of variation. Hierarchical analy sis of gene diversity for each species shows that 84% to 100% of the t otal gene diversity resides within populations while only 0% to 16% ar e due to variation between populations. In the 'fusca' group as a whol e, the between-population component of gene diversity amounts to 52.0% and is much higher than in any single species including N. menziesii (12.3%). Comparison of observed and expected frequencies of heterozygo tes gave no significant deviation from HARDY-WEINBERG equilibrium indi cating predominant cross-pollination in both N. menziesii and the 'fus ca' group species.