QTL studies confirm genetic independence of growth and wood density in tropical pine hybrids

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.