There is world-wide interest in developing hybrids between the major
temperate plantation species Eucalyptus globulus and E. nitens
for plantation development in areas too cold for E. globulus. A ten-year
study of the performance of interspecific and intra-provenance F1 hybrid
populations of E. globulus and E. nitens has shown that
quantitative genetic models used for genetic evaluation of growth in
pure species are not appropriate for interspecific hybrid populations.
Additive genetic effects expressed in E. globulus intra-provenance
populations for growth are also expressed in the inter-provenance hybrid
population, with levels intermediate between the two parental populations.
However there is no such association in an E. nitens x globulus
hybrid population. Comparable estimates of these additive genetic effects
are highly inflated in the hybrid populations, suggesting that different
genes or gene interactions are affecting hybrid performance.
The field trial studied was established by CSIRO Forestry and Forest
Products and North Forest Products (now Gunns Limited) in 1990 near
Ridgley, Tasmania and has been regularly monitored by CRC scientists.
It is one of the best hybrid eucalypt trials established and includes
crosses within and between provenances of the pure species and interspecific
hybrids, with the same parents being used for both within and between
The interspecific hybrid population was characterised by atypically
high levels of seedling abnormalities and high mortality in the nursery
and field. The average performance of survivors was below the mid-parent
value (i.e. negative heterosis). In contrast, hybrids between the Taranna
and King Island provenances of E. globulus exhibited high survival
and average performance well above the mid-parental value, although
they did not perform better than the faster growing King Island crosses.
The study showed large differences between the Taranna and King Island
provenances in their propensity for hybridisation with E. nitens,
with most of the poorer performing interspecific hybrid families derived
from crosses with Taranna E. globulus. In contrast to growth,
wood density measured indirectly using Pilodyn penetration exhibited
more typical quantitative genetic behaviour in the inter-specific F1
hybrid and was always intermediate or comparable with one or other of
the parent species. The inter-specific F1 hybrid did not show any significant
advantage over either of the parental species at this site. They did
not show any combination of superior growth or wood density that could
not be found within the parental species even though there was one outstanding
inter-specific F1 hybrid family for growth.
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21 May, 2003