Age trends in variances and heritabilities for diameter and height in maritime pine (Pinus pinaster Ait.) in Western Australia

The inheritance of variables related to growth was studied in a progeny trial of maritime pine (Pinus pinaster AIT.) in Wanneroo, Western Australia. The trial consists of the progeny of three parent trees used as females and five used as males, crossed in 14 of the 15 possible combinations (full-sib families), plus a routine commercial control family. There were 108 trees/cross, planted at a spacing of 3 m x 3 m. Certain families had consistently large diameters and were consistently tall, indicating that early selection between families may be effective. Genetic and environmental variance components of the diameters and heights were estimated using the restricted maximum likelihood (REML) method. Both phenotypic and additive-genetic variances increased as trees became older, rapidly up to age 6 years, then more gradually up to 25 years. However, the heritabilities were fairly constant, in the range 0.14 to 0.16 for diameter and 0.11 to 0.14 for height. This is in contrast to other studies of pines in which heritability increased with age, and was greater for height than for diameter. In a principal component analysis of the diameters the first component represented an average of the successive measurements and accounted for 93% of the variation. The second component contrasted early and late measurements and accounted for only 6% of the variation, but was more heritable (h(2) = 0.35) than the first component (h(2) = 0.14). A similar pattern was found for the heights. It is concluded that selection between families at an early age for diameter or height will be effective. It is also suggested that the second principal components reflect the genetic distance between trees, and could be used to ensure retention of genetic diversity in a tree breeding program.