ABSTRACT
Queensland Alliance for Agriculture and Food innovation, University of Queensland, Brisbane, QLD 4072, Australia. *Corresponding author: adam.healey@uq.net.au
The eucalypt taxa (Eucalyptus, Corymbia and Angrophora) contains over 900 species, belonging to the angiosperm family, Myrtaceae (Shepherd et al. 2011). Eucalypts are diploid organisms with a haploid chromosome number of 11 (Myburg et al. 2007; Grattapaglia and Kirst 2008; Grattapaglia et al. 2012). Their genome size, fi rst estimated by Grattapaglia and Bradshaw (1994) by flow cytometry with chicken erythrocytes, ranges between 350-700 mega-base pairs (Mbp). The Symphyomyrtus subspecies of Eucalyptus (E. grandis, E. globulus, E. camaldulensis, E. tereticornis, E. robusta, and E. urophylla) have a genome size of approximately 650 Mbp, with E. saligna having the largest genome at 710 Mbp. E. globulus and E. dunnii had a smaller estimated genome size of 530 Mbp, although re-estimation of E. globulus genome size in 2004 by Pinto et al. (2004) revealed an average size of 644 Mbp when compared to plant standard, Lycospersicon esculentum. Corymbia citriodora and Corymbia torelliana genome sizes were the smallest of those examined, approximately 380 Mbp, although the Angophora genome was not investigated. Hybrid progeny of Eucalyptus and Corymbia (E. grandis X E. urophylla, E. grandis X E. camaldulensis, E. tereticornis X E. grandis, E. urophylla X E. alba, C. citriodora X C. torelliana) showed similar genetic contents to their parents and no indication of polyploidy (Grattapaglia and Bradshaw 1994). Although different techniques for estimating eucalypt genome size can produce varying results, true genome size cannot be determined without sequencing. The average eucalypt genome is slightly larger than some other fully sequenced plant species, Arabidopsis thaliana (125 Mbp) (The Arabidopsis Genome Initiative 2000), two varieties of Oryza sativa (420-460 Mbp) (Goff et al. 2002; Yu et al. 2002) and Populus trichocarpa (485 Mbp) (Tuskan et al. 2006), while considerably smaller than the large, repetitive Pinus genome (20,000-26,000 Mbp) (Ahuja 2001; Bogunic et al. 2003).
