80 research outputs found
Exploration of the Eucalyptus globulus gene pool
The first Europeans to discover Eucalyptus
globulus were French explorers in 1792. Its seed
was rapidly spread throughout the world in the
19th century and this was the species by which
much of the world first knew the genus.
However, it was in the industrial forests of the
20th century that this species, once considered
the ‘Prince of Eucalypts’, achieved greatest
prominence due to its fast growth and superior
pulp qualities. Formal breeding first commenced
in 1966 in Portugal and in the late 1980’s large
base population trials from open-pollinated seed
collections from native stands were established
in many countries. These trials have provided
unprecedented insights into the quantitative
genetic control of numerous traits of economic
and ecological importance and how this variation
is spatially distributed in the native range of the
species. However with large, fully pedigreed
breeding populations becoming available for
quantitative analysis and the rapidly expanding
knowledge of DNA sequence variation, we are
now at the threshold of a new understanding of
this important eucalypt gene pool. Indications of
the significance of non-additive genetic effects
are becoming available. The E. globulus
chloroplast genome has now been sequenced
and several genome maps have been published.
Studies of the variation in nuclear microsatellites
and the lignin biosynthesis gene CCR confirm
the complex, spatially structured nature of the
native gene pool. Strong spatial structuring of
the chloroplast genome has provided a tool for
tracking seed migration and the geographic
origin of exotic landraces. Highly divergent
lineages of chloroplast DNA have been
discovered and studies of the hypervariable JLA+
region argue that some components of the E.
globulus gene pool have been assimilated from
other species following hybridisation
Genetic parameters for growth, wood density and pulp yield in Eucalyptus globulus
Genetic variation and co-variation among the key
pulpwood selection traits for Eucalyptus globulus were
estimated for a range of sites in Portugal, with the aim of
improving genetic parameters used to predict breeding
values and correlated response to selection. The trials
comprised clonally replicated full-sib families (eight trials)
and unrelated clones (17 trials), and exhibited varying
levels of pedigree connectivity. The traits studied were stem
diameter at breast height, Pilodyn penetration (an indirect
measure of wood basic density) and near infrared reflectance
predicted pulp yield. Univariate and multivariate
linear mixed models were fitted within and across sites, and estimates of additive genetic, total genetic, environmental
and phenotypic variances and covariances were obtained.
All traits studied exhibited significant levels of additive
genetic variation. The average estimated within-site narrowsense
heritability was 0.19±0.03 for diameter and 0.29±
0.03 for Pilodyn penetration, and the pooled estimate for
predicted pulp yield was 0.42±0.14. When they could be
tested, dominance and epistatic effects were generally not
statistically significant, although broad-sense heritability
estimates were slightly higher than narrow-sense heritability
estimates. Averaged across trials, positive additive
(0.64±0.08), total genetic (0.58±0.04), environmental
(0.38±0.03) and phenotypic (0.43±0.02) correlation estimates
were consistently obtained between diameter and
Pilodyn penetration. This data argues for at least some form
of pleiotropic relationship between these two traits and that
selection for fast growth will adversely affect wood density
in this population. Estimates of the across-site genetic
correlations for diameter and Pilodyn penetration were
high, indicating that the genotype by environment interaction
is low across the range of sites tested. This result
supports the use of single aggregated selection criteria for
growth and wood density across planting environments in
Portugal, as opposed to having to select for performance in
different environment
A Switch in the Control of Growth of the Wing Imaginal Disks of Manduca sexta
Background: Insulin and ecdysone are the key extrinsic regulators of growth for the wing imaginal disks of insects. In vitro tissue culture studies have shown that these two growth regulators act synergistically: either factor alone stimulates only limited growth, but together they stimulate disks to grow at a rate identical to that observed in situ. It is generally thought that insulin signaling links growth to nutrition, and that starvation stops growth because it inhibits insulin secretion. At the end of larval life feeding stops but the disks continue to grow, so at that time disk growth has become uncoupled from nutrition. We sought to determine at exactly what point in development this uncoupling occurs. Methodology: Growth and cell proliferation in the wing imaginal disks and hemolymph carbohydrate concentrations were measured at various stages in the last larval instar under experimental conditions of starvation, ligation, rescue, and hormone treatment. Principal Findings: Here we show that in the last larval instar of M. sexta, the uncoupling of nutrition and growth occurs as the larva passes the critical weight. Before this time, starvation causes a decline in hemolymph glucose and trehalose and a cessation of wing imaginal disks growth, which can be rescued by injections of trehalose. After the critical weight the trehalose response to starvation disappears, and the expression of insulin becomes decoupled from nutrition. After the critical weight the wing disks loose their sensitivity to repression by juvenile hormone, and factors from the abdomen, bu
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