Intra- and interspecific allozyme variation in eucalypts from the spotted gum group, Corymbia, section 'Politaria (Myrtaceae)

The distribution of genetic variation within and among species in Corymbia section `Politaria' was examined using allozymes. This section consists of four species, Corymbia citriodora (Hook.) K. D. Hill & L. A. S. Johnson, C. maculata (Hook.) K. D. Hill & L. A. S. Johnson, C. henryi (Blake) K. D. Hi ll & L. A. S. Johnson and C. variegata (F. Muell.) K. D. Hill & L. A. S. Jo hnson, which are of commercial interest for plantation and farm forestry. T hirty populations representing the species' range-wide distributions were s tudied, extending from upland tropical regions of north Queensland, south t o eastern Victoria. Despite relatively low allozyme divergence between spec ies, there was a relationship between geographic distribution patterns of p opulations and allozyme variation. The section was shown to comprise very c losely related species with only 15% of the total genetic diversity attribu ted to differences between species. Two distinct genetic alliances were evi dent: C. maculata-C. henryi and C. citriodora-C. variegata. Corymbia citrio dora and C. variegata, however, could not be distinguished by their allozym e profiles. The lack of genetic differentiation between these taxa suggests that they represent one species composed of two chemical races. Corymbia m aculata and C. henryi were shown to be closely allied but genetically disti nct. Corymbia henryi had the highest genetic diversity in the group and low est differentiation among populations, while C. maculata had the lowest div ersity but the highest genetic differentiation among populations. There was evidence of isolation-by-distance among populations of C. citriodora, C. m aculata and C. variegata but not in C. henryi, which has a smaller geograph ic range. The inclusion in the study of C. torelliana (F. Muell.) K. D. Hil l & L. A. S. Johnson as an outgroup accentuated the small genetic differenc es between species in the group. The patterns of genetic diversity are disc ussed in relation to the species' taxonomic relationships, breeding systems and utilisation.