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Recommended sampling intensity for phenotyping durable eucalypt breeding trials for heartwood quality

By Clemens Altaner, March 2021.

Download SWP-T121 (pdf)

Executive summary

The available heartwood quantity (diameter at 0.5 m stem height) and heartwood quality (NIR predicted extractive content) for ten NZDFI breeding trials was analysed with the intention to optimise sampling intensity and consequently reduce resource demands. Heartwood phenotyping is resource intensive and requires older/bigger trees delaying selection decisions and extending breeding cycles.

The analysis concluded that accurate family and individual tree breeding values for heartwood quality can be obtained from the assessment of the heartwood obtained from 8 individuals per family and collecting 6 NIR spectra on each heartwood sample.

Trees suitable for heartwood phenotyping have developed at least 30 mm of heartwood diameter, in order to acquire 6 NIR spectra. Heartwood formation was dependent on tree size, not tree age, with noticeable differences between species and sites.

The proportion of trees in a trial having developed sufficient heartwood for phenotyping (i.e. 30 mm) depended on their size. This proportion was calculated by combining the likelihood of a tree having developed heartwood depending on its diameter and the distribution of diameters in the trial. In turn, this allowed the determination of the number of trees which need to be cored to obtain in average the required number of heartwood samples (i.e. 8).

As corelength (under-bark diameter at 0.5 m stem height) is an impractical measure to decide the timing for heartwood phenotyping, the linear correlations to diameter at breast height (DBH) were established for the species. This allowed the determination of the required number of trees, which need to be cored to obtain the necessary heartwood samples from the most recent growth (i.e. DBH) assessments.

Heartwood phenotyping was costed. Field sampling of a stem core required at least NZ$ 12 and the price of obtaining the extractive content from 6 NIR spectra was NZ$ 4. The phenotyping costs per family in a trial under the above determined conditions can be as low as NZ$ 125 but increase significantly if smaller trees are sampled or the coring equipment is not well maintained.


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