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ABSTRACT
Variation in 12 morphological and growth characteristics were assessed in 3.5-month-old Corymbia citriodora subsp. citriodora seedlings. The taxon is known as C. citriodora throughout this paper. The seedlings originated from 147 families and one multiple-parent bulk seedlot representing six natural stand seed sources and six Chinese landrace seed sources. Traits assessed included presence of lignotubers, leaf insect and disease damage, stem pubescence, leaf pubescence, the ratio of leaf length to width at nodes 3 and 6, length from the base to widest point of leaves at nodes 3 and 6, seedling height and root collar diameter. Significant differences (P < 0.01) were found between seed sources for most of the characteristics assessed, and between families within seed sources.
The most useful individual traits for discriminating between seed sources were stem and leaf pubescence. Seed sources and families from the northern-most parts of the species natural range in Far North Queensland, Australia, had significantly higher stem pubescence (i.e. hairier stems) but lower leaf pubescence (less hairy leaves) than the other two Queensland seed sources (North Queensland and Central Queensland) and the six Chinese seed sources. Principal component analysis suggested clear patterns of geographic variation between seed sources from the natural distribution and between the Chinese seed sources. By this analysis, the five seed sources from Guangxi and Guangdong provinces in China appeared to form a group separated from a seed source from Yunnan province; the latter source was placed closest to a natural stand seed source from the southern part of the species range in North Queensland. The closest natural stand source to the five Guangxi and Guangdong seed sources was one from Central Queensland. The implications of the study’s findings for developing a breeding population from the study material are discussed.
Acknowledgements
Funding for this study was provided through a series of projects, including a Chinese forestry public benefit special project ‘Breeding cultivation technologies for superior eucalypt species for solid wood end-products’ (Project number 2015-4-204), and a People’s Republic of China State Forestry Administration foreign science and technology introduction project ‘Introduction and breeding technologies for drought tolerance eucalypt germplasm’ (Project number 2012-4-50). We are grateful to Guangxi Gaofeng Forest Farm, Guangxi Dongmen Forest Farm and South China Agriculture University for assistance in collecting some of the Chinese seedlots. Two anonymous reviewers provided numerous suggestions for significantly improving the content of this paper and we appreciate their guidance.