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 putative loci. Results of isozyme analysis are supportive of the present taxonomic concept and reveal a major genetic divergence between N. menziesii and the remaining four species which belong to the 'fusca' group and form natural hybrids among each other. Genetic variation in N. menziesii is distinctly higher than in any of the 'fusca' group species where N. fusca shows the lowest levels of variation. Hierarchical analysis of gene diversity for each species shows that 84% to 100% of the total gene diversity resides within populations while only 0% to 16% are due to variation between populations. In the 'fusca' group as a whole, 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 heterozygotes gave no significant deviation from HARDY-WEINBERG equilibrium indicating predominant cross-pollination in both N. menziesii and the 'fusca' group species.