Farm Forestry New ZealandEarly Heartwood Screening by Wounding
By Gayatri Mishra, Yanjie Li and Clemens Altaner, June 2017.
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Executive summary
Trees can be screened at age (1-2 years) for wood properties such as growth stress, collapse, density or stiffness (Chauhan and Entwistle, 2010; Chauhan et al., 2013). Early selection reduces trial costs, shortens breeding cycles and ensures timely deployment of improved material. Early selection for heartwood is challenging because heartwood formation in eucalypts only starts at age ~5. Early selection for heartwood would be possible if a strong correlation of heartwood to another tree feature is found.
The wound response of trees has similarities to heartwood formation. Extractives deposited in wound wood originate from a similar metabolic pathway as heartwood. Therefore, the wound response could be correlated to heartwood formation. A strong correlation would allow screening eucalypts for heartwood at age 1-2, i.e. before heartwood is formed. The correlation between heartwood features and the wound reaction of the offspring has been investigated for Pinus sylvestris (Harju et al., 2009). They reported a heritability of 0.31 between the pinosylvin, a heartwood compound, concentration in the wound wood of the offspring and that in the heartwood of the mother trees. These results suggested that early testing for heartwood durability may be possible in a breeding programme.
The extension of the axial wound response of ~2-year old E. bosistoana seedlings was found to be heritable (h2=0.26 with a 95% credibility interval of 0.00 to 0.53). However, no correlation between the axial wound response in the ~2-year old seedlings and heartwood diameter or extractive content in 7-year old trees was found. Therefore it is not possible to assess heartwood formation early in a breeding programme by measuring the axial wound response in 2-year old seedlings.
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