NUCLEAR-DNA CONTENT OF COMMERCIALLY IMPORTANT EUCALYPTUS SPECIES AND HYBRIDS

This paper reports the nuclear DNA content estimates obtained by flow cytometry for a group of twelve Eucalyptus species and five fast-growi ng hybrids that includes those most widely planted throughout the worl d. Estimates of nuclear (2C) DNA content for the species surveyed rang ed from 0.77 pg/2C for Eucalyptus citriodora Hook. (subgenus Corymbia) to 1.47 pg/2C for Eucalyptus saligna Smith (subgenus Symphyomyrtus). This range corresponds to a haploid genome size range of 370-700 megab ase pairs. The average physical equivalent of a 1 cM distance could be as low as 200 kilobase pairs in Eucalyptus, an attractive feature for positional cloning efforts in woody plants. The closer the species we re in phylogenetic relationship the more similar were their nuclear DN A content values. All the interspecific hybrids surveyed displayed a n uclear DNA content in the expected intermediate range between the resp ective parental species, with the exception of one originating from Ri o Claro, Brazil, whose exact parentage is unknown. No evidence of poly ploidy was observed in any of the hybrids. The flow cytometry procedur e employed in this study is an efficient method for investigating ploi dy levels of high yielding hybrids of Eucalyptus.