Abstract

The distribution of genetic variation within and among species inCorymbia 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.Hill & L.A.S.Johnson and C. variegata (F.Muell.) K.D.Hill & L.A.S.Johnson, which are of commercial interest for plantation and farmforestry. Thirty populations representing the species’ range-widedistributions were studied, extending from upland tropical regions of northQueensland, south to eastern Victoria. Despite relatively low allozymedivergence between species, there was a relationship between geographicdistribution patterns of populations and allozyme variation. The section wasshown to comprise very closely related species with only 15% of thetotal genetic diversity attributed to differences between species. Twodistinct genetic alliances were evident:C. maculata–C. henryi andC. citriodora–C. variegata.Corymbia citriodora andC. variegata, however, could not be distinguished bytheir allozyme profiles. The lack of genetic differentiation between thesetaxa suggests that they represent one species composed of two chemical races.Corymbia maculata and C. henryiwere shown to be closely allied but genetically distinct.Corymbia henryi had the highest genetic diversity in thegroup and lowest differentiation among populations, whileC. maculata had the lowest diversity but the highestgenetic differentiation among populations. There was evidence ofisolation-by-distance among populations ofC. citriodora, C. maculata andC. variegata but not in C. henryi,which has a smaller geographic range. The inclusion in the study ofC. torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson asan outgroup accentuated the small genetic differences between species in thegroup. The patterns of genetic diversity are discussed in relation to thespecies’ taxonomic relationships, breeding systems and utilisation.