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Abstract

This project examined silvicultural and environment factors which affect precocious and
abundant flowering in trees of the economically important plantation species Eucalyptus
nitens with the aim of optimising seed production.
Two separate studies were undertaken to examine how flowering and seed quality were
affected by the macroenvironment. The first studied an altitudinal gradient which would
span the range where operational seed orchards might be located. Flowering abundance
and seed production was greatest on sites where growth rate was highest. Seed weight,
germination success and germination rate decreased as site altitude increased. The second
study examined the effects of water availability. Flowering abundance was highest in
trees experiencing water stress, whilst seed quality remained unaffected by parental water
status. Overall, the maternal tree had a greater influence on seed quality traits than the
environmental effects studied.
On the microenvironmental scale, the effect of tree spacing on flower abundance and
capsule survival was studied at two sites where trees were 5 and 13 years old. As the
spacing between trees increased so too did reproductive yield, not only per tree but also
per hectare. Furthermore, it appears that as trees mature, tree density needs to be
decreased to maintain the maximum reproductive yield per hectare.
To overcome the strong genetic control of flowering precocity a hormone manipulation
approach was tested. The gibberellin biosynthesis inhibitors paclobutrazol, chlormequat
chloride and prohexadione were applied to seedlings and their relative effects compared.
These treatments reduced both growth rate and endogenous levels of GA1 to varying
degrees, with paclobutrazol the most effective. However, none of the treatments
promoted precocious flowering. Further environmental and/or chemical manipulation
would be required to induce precocious flowering in E. nitens seedlings.
The application of nitrogen fertiliser to juvenile trees stimulated precocious and abundant
flowering. This was due in part to accelerated growth rate but nitrogen also acted
independently of growth rate. In contrast, phosphorus had no effect on growth or
reproductive output but did cause trees to undertake vegetative phase change earlier.
Nitrogen fertiliser combined with hormone manipulation with paclobutrazol was applied to
juvenile and mature plantation grown trees to promote precocious and abundant flowering.
There was an additive effect in combining the treatments in promoting both precocious and
abundant flowering.
The production of pedigree seed traditionally required three visits to the mother tree to
carry out controlled pollination. To improve the efficiency of this process, a number of
novel controlled pollination procedures were tested on both E. nitens and E. globulus. A
new single visit pollination protocol for E. globulus was successfully developed, whilst
the techniques applied to E. nitens yielded no advantage over the traditional method. This
new protocol for E. globulus is expected to reduce the cost of pedigreed seed production
by more than half.
This thesis identifies a number of beneficial practices which will improve the productivity
and economic performance of E. nitens seed orchards.

Item Type:	Thesis - PhD
Authors/Creators:	Williams, DR
Keywords:	Eucalyptus
Copyright Holders:	The Author
Copyright Information:	Copyright 2000 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Chapter 4 appears to be the equivalent of a pre or post print of an article published as: Williams, D.R., Ross, J.J., Reid, J.B. and Potts, B.M. (1999), Response of Eucalyptus nitens seedlings to gibberellin biosynthesis inhibitors, Plant growth regulation, 27: 125-129. The final publication is available at Springer via http://dx.doi.org/10.1023/A:1006176928861 Chapter 6 appears to be the equivalent of a pre or post print of an article published as: Williams, D.R., Potts, B.M. and Black P.G. (1999). Testing single visit pollination procedures for Eucalyptus globulus and E. nitens. Australian Forestry 62: 346-352. The Version of Record of this manuscript has been published and is available in Australian forestry 19/8/1999 (online 15/4/2013) http://www.tandfonline.com/10.1080/00049158.1999.10674802
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