Heritabilities and genetic correlations for estimated growth curve parameters in maritime pine

Height growth curves and several other characters were measured in five maritime pine (Pinus pinaster Ait) progeny tests aged from 18 to 27 years (about half the rotation age), with sample sizes of 272–1555 trees. These curves were fitted with a reparametrized Lundqvist-Matèrn sigmoidal growth function with global estimation of two of the four parameters. Each curve was characterized by two parameters:

the maximal growth rate (r), approximately proportional to the stem height at age 16 years, and essentially determined by the height increments around age 6 years.

the asymptote (A), which is an extrapolation of growth after the measurement age. A is essentially determined by the latter growth period (around age 20 years), and is also related to the shape of the observed curve.

The modelling framework appeared to be well suited to the characteristics of the data studied, and the estimation standard errors of the parameters were reasonably low. The heritabilities yielded for the growth curve parameters were high, similar to the heritabilities of cumulative heights. The genetic correlation between r and A was low, pointing to a poor juvenile-mature correlation. Discrepancies from one trial to another in heritabilities and in the correlation pattern were observed, they probably originated from environmental stresses. Maritime pine is actually selected using height and butt angle of lean at age 10 years as criteria. Improvements in the breeding program are suggested.