Wounding response in xylem of Scots pine seedlings shows wide genetic variation and connection with the constitutive defence of heartwood.

In this greenhouse experiment, 3-year-old Scots pine (Pinus sylvestris L.) seedlings were wounded by drilling holes through the stem. In the xylem next to the wound, the concentration of resin acids (RAC) increased, and the production of extractives typical for heartwood (stilbenes) and knotwood (stilbenes and lignans) of mature trees was induced. The induced stilbenes were pinosylvin (PS) and pinosylvin monomethyl ether (PSM), and the lignans nortrachelogenin (NTG) and matairesinol (MR). There was positive phenotypic correlation between concentrations of the different extractives. Except for the RAC, the extractive concentrations showed no correlation with the size of the seedlings. The treated seedlings belonged to half-sib families, which enabled the estimation of the genetic parameters for the response variables. The proportion of heritable variation (heritability, h(2)) in the concentration of PS, NTG and MR varied between 0.71 and 1.03, whereas for PSM and RAC the heritability was lower (0.35 and 0.31). Genetic correlation was significant between PS and PSM (r = 0.55, P = 0.018), and between NTG and MR (r = 0.50, P = 0.033). Heritabilities were also estimated on the basis of the regression of the offspring on their mothers h(2)(0P). These estimates were assessed for the concentration of PS, PSM and RAC in the wound response area of the seedlings and correspondingly in the heartwood of their mothers. The heritability was highest for the concentration of PS h(2)(0P). The findings of this study support the suggestion that the wounding of Scots pine seedlings may facilitate the development of an early testing method for breeding heartwood durability.