Additive genetic variation in Pinus radiata bark chemistry and the chemical traits associated with variation in mammalian bark stripping.

Secondary metabolites are suggested as a major mechanism explaining genetic variation in herbivory levels in Pinus radiata. The potential to incorporate these chemical traits into breeding/deployment programmes partly depends on the presence of additive genetic variation for the relevant chemical traits. In this study, near-infrared spectroscopy was used to quantify the constitutive and induced levels of 54 compounds in the bark of trees from 74 P. radiata full-sib families. The trees sampled for chemistry were protected from browsing and induced levels were obtained by subjecting half of the trees to artificial bark stripping. The treatment effect on bark chemistry was assessed along with narrow-sense heritability, the significance of non-additive genetic effects and the additive genetic correlations of compounds with bark stripping by mammalian herbivores that was observed in unprotected replicates of the field trial. The results indicated: (i) significant additive genetic variation, with low-moderate narrow-sense heritability estimates for most compounds; (ii) while significant induced effects were detected for some chemicals, no significant genetic variation in inducibility was detected; and (iii) sugars, fatty acids and a diterpenoid positively genetically correlated while a sesquiterpenoid negatively genetically correlated with bark stripping by the mammalian herbivore, the Bennett's wallaby (Macropus rufogriseus). At the onset of browsing, a trade-off with height was detected for selecting higher amounts of this sesquiterpenoid. However, overall, results showed potential to incorporate chemical traits into breeding/deployment programmes. The quantitative genetic analyses of the near infrared predicted chemical traits produced associations with mammalian bark stripping that mostly conform with those obtained using standard wet chemistry.