Relationship of heartwood traits with diameter growth, implications for genetic selection in Pinus radiata

Abstract

The heartwood of radiata pine (Pinus radiata D. Don) is not favoured commercially because of its darker appearance, unreliable durability and difficulty to treat chemically; consequently, light-coloured sapwood, which is more easily treated with decay-resistant chemicals, is of more value. To decrease the amount of heartwood or increase sapwood cross-sectional area by genetic selection, the genetics of sapwood cross-sectional area (SWA), sapwood area percentage (SWAP) and number of heartwood rings (HWR) is of interest. We investigated genetic variation in these three variables from increment cores from trees from two trial series, each planted at two sites, from a total of some 330 families (189 were half-sib and 142 were full-sib) with 10 to 30 individuals assessed per family. Trials were assessed between 16 and 23 years old when all trees had started to develop heartwood. The three sapwood-related traits were moderately heritable across pairs of sites (${\widehat{h}}_i^2$ = 0.2 to 0.4) indicating opportunity for selection. SWA was strongly correlated (r _a  = 0.9) with diameter. SWAP and HWR were also strongly correlated (r _a  = −0.9). The number of HWR was independent of tree diameter, providing the opportunity through genetic selection to reduce heartwood area whilst increasing tree growth rate.