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Advice on Publications Available.Melaleuca alternifolia
is a commercially important Australian species which is harvested from natural stands and plantations for the production of tea tree oil. The variability of plantation yields has focussed attention on the need to develop a breeding program for the industry.The studies in this thesis describe the pattern of genetic variation in Melaleuca alternifolia and examine the evolutionary relationships with the partially sympatric species M. linariifolia and M. trichostachya. Variation in oil production traits are assessed and the gains that could be expected from a breeding program determined.
M. alternifolia
occurs on seasonally inundated sites in north-eastern NSW and along permanent watercourses in southeastern Queensland. The species has a relatively narrow distribution with disjunctions in its geographic range. Analysis of allozymes revealed levels of genetic variation which were comparable with other Australian tree species. The level of differentiation among populations was low (DPT=0.12), associated with a high outcrossing rate (t=0.93) and high levels of gene flow. However, there was clear evidence from both leaf oils and allozymes of genetic differentiation of the Queensland populations. These differences correspond with geographic and habitat differences.There was considerable variation in leaf oil composition within M. alternifolia and five chemical forms are described. The Queensland populations produced a terpinolene leaf oil of similar composition to M. trichostachya, while NSW populations produced terpinen-4-ol and 1,8-cineole rich oils. Commercial production is restricted to terpinen-4-ol 'Type' oils. Seed sources of 'Type' trees were identified in the NSW populations which can be utilised to increase the genetic diversity and productivity of plantations.
RFLP analysis of variation in the chloroplast genome of M. alternifolia, M. linariifolia and M. trichostachya revealed close evolutionary links between M. alternifolia and southern populations of M. linariifolia. Based on evidence from leaf oils and chloroplast DNA the Port Macquarie population of M. alternifolia appears to be a hybrid population which obtained its chloroplast genome from southern populations of M. linariifolia. A high level of nucleotide diversity was recorded within M. linariifolia reflecting divergence of a northern and southern lineage. The level of divergence was higher than between M. alternifolia and southern populations of M. linariifolia. The chloroplast genome of M. trichostachya was distinct from both M. alternifolia and M. linariifolia, suggesting similarities in oil composition between the two taxa were not due to hybridisation between these species.
To determine the gains that could be expected in a breeding program, variation in leaf oil yield and composition, plant biomass production and coppicing were examined in a provenance/progeny trial established on a commercial plantation in northeastern NSW. The wide range of variation in these characters, together with a high heritability for oil yield (0.67) and moderate heritabilities for plant dry weight (0.25) and coppicing (0.27) indicate substantial gains could be made by breeding for any one trait. However negative genetic correlations between oil yield and plant dry weight imply that gains will have to be balanced between traits. Using combined index selection with a restriction to maintain plant biomass at pre-selection levels, gains of 17% in oil yield and 14% in coppicing could be expected from one generation of breeding at an intensity of one tree in ten. Gains of 23% for oil yield and 18% for coppicing could be expected in a clonal seed orchard from selection of the best 20 individuals from the progeny trial. The results from these studies provide the basis for development of a breeding program to improve the productivity of tea tree plantations.
Any claims made by authors in the Australian New Crops Newsletter are presented by the Editors in good faith. Readers would be wise to critically examine the circumstances associated with any claims to determine the applicability of such claims to their specific set of circumstances. This material can be reproduced, with the provision that the source and the author (or editors, if applicable) are acknowledged and the use is for information or educational purposes. Contact with the original author is probably wise since the material may require updating or amendment if used in other publications. Material sourced from the Australian New Crops Newsletter cannot be used out of context or for commercial purposes not related to its original purpose in the newsletter
Contact: Dr Rob Fletcher, School of Land and Food, The University of Queensland Gatton College, 4345; Telephone: 07 5460 1311 or 07 5460 1301; Facsimile: 07 5460 1112; International facsimile: 61 7 5460 1112; Email:
r.fletcher@mailbox.uq.edu.au[
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