This thesis examines the quantitative genetics of intra- and inter-specific
hybrids of E. globzllus ssp. globl~lus and E. nitens. The trials established to make
this study are unique in forestry, due to the fact that the same parents have
been used in open-pollination, intra- and inter-provenance (or intra-species)
crosses and inter-species F1 hybrids. This has allowed direct comparison of
genetic parameters derived from different cross types. The traits examined
include frost resistance using an electrical conductivity method, growth
(diameter at breast height over bark DBHOB, at ages 2, 3, 4, 6 and 10 years)
and Pilodyn penetration at age 6 years as an indirect measure of wood density.
The results demonstrate that the measured performance of frost, growth and
Pilodyn traits in the inter-specific Fi hybrid E. nitens x globulus is always
intermediate or comparable with one or other of the parent species. In the
frost trait, the inter-specific hybrid was no better than the frost sensitive E.
globulus, so there is no overall advantage in producing the hybrid for this trait.
Negative mid-parent heterosis was observed for early age growth traits in
inter-specific E. nitens x globulus FI hybrids involving Taranna E. globulus male
parents. The inter-specific FI hybrids demonstrated generally poor survival
and a high proportion of abnormal and slow growing phenotypes, which
eventually died. This latter phenomenon was not evident in pure species
crosses, either within or between provenances.
It is shown that in E. globulus open-pollinated progeny estimates of additive
genetic parameters are inflated and that breeding values for growth in E.
globulus are poorly estimated, possibly due to the confounding effects of
variation in inbreeding. This was not the case for traits of high heritability
such as Pilodyn. Within the E. nitens population studied, open-pollinated
estimates compared well with control-pollinated estimates for all traits.
Genetic parameter estimates from control-pollinated progeny indicate low
heritability for growth in E. globulus which diminish over time. Dominance
effects were low and comparable with additive genetic effects but were site
specific. In E. nitens heritability for growth is moderate to high, tending to
increase over time with significantly low levels of dominance, which diminish
over time. Pilodyn has low to moderate heritabilities with low levels of
dominance in both species. Moderate levels of heritability were demonstrated
for frost resistance in both species, but dominance effects could not be
accurately estimated.
The correlation of performance of parents in intia-specific crosses through
their General Combining Ability (GCA) is compared with performance in
inter-specific hybrids through General Hybridising Ability (GHA). It is shown
that there is little or no correlation between GCA and GHA in inter-specific F1
hybrids for growth or frost resistance, but there was a good correlation for
Pilodyn. This indicates that, for growth and frost resistance, there may be
different genes, which contribute to expression between species and these may
not combine according to classical quantitative genetic theory. In contrast,
within E. globulus there was very high correlation of within-provenance GCA
with between-provenance GHA for growth and Pilodyn, indicating the same
genes are acting within the species, regardless of provenance.
It is demonstrated that standard quantitative genetic models do not cope
adequately with inter-specific F1 hybrid populations for growth traits in this
case. In addition, the implication for breeding and deployment of interspecific
Fi hybrids is compromised by the lack of ability to predict
performance of potential hybrid combinations from pure species performance
of parents.
| Identifer | oai:union.ndltd.org:ADTP/246242 |
| Date | January 2002 |
| Creators | Volker, PW |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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