studies confirm genetic independence of growth and wood density in tropical
Studies which map the location and relationships amongst genes in the
genomes of tropical pine hybrids are providing more targeted approaches
for tree improvement. A recently completed study of the gene effects,
or quantitative trait loci (QTL), that control tree growth and wood
density in the parents of a Slash pine by Caribbean pine hybrid, has
shown that they generally do not occur close together on genetic maps
of the parents. While putative QTL that affect trunk ring width, early
season and late season components of a ring tended to cluster together,
they generally did not occur near those that affected ring density.
This suggests that these characters are largely controlled by separate
sets of genes that are not located close together in the genome.
This means the genes for the different characters tend to be inherited
independent of one another, and individuals with favourable combinations
of growth and wood density characters should be readily identified in
offspring from parents in the existing breeding populations, without
recourse to new parents and new genes. These findings are consistent
with field measurements of these characters that have also shown a lack
of genetic correlation between growth and density in this hybrid. Negative
relationships between growth rates and wood density are a key issue
for the genetic improvement of some of the world's major plantation
species including Pinus caribaea and P. radiata because
they create an impediment to simultaneous gains in both characters.
Quantitative trait loci analysis is providing new insight into the relationships
between growth and wood density in trees by revealing the distributions
and interactions amongst genes that control these characters.
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21 May, 2003