An approach to quantify natural durability of Eucalyptus bosistoana by near infrared spectroscopy for genetic selection

https://doi.org/10.1016/j.indcrop.2020.112676Get rights and content

Highlights

  • More and less decay resistant E. bosistoana heartwood was quickly and non-destructively distinguished by near-infrared spectroscopy.

  • This method allowed the identification of genetics with superior decay resistance in an E. bosistoana breeding program.

  • Near-infrared spectroscopy also has potential for quality control of natural durability of timber by segregation.

Abstract

Natural durability within a timber species can be variable. Hence efficient assessments of natural durability are required to ensure quality either through tree breeding or segregation during production. In this study, first the relationship between extractive content and mass loss of Eucalyptus bosistoana heartwood caused by a white and a brown-rot fungus was validated. Then the ability of NIR spectroscopy as a high-throughput method to evaluate heartwood decay resistance was examined. Finally the NIR method was applied to a tree breeding trial. A correlation between extractive content and mass loss against the white-rot fungus (Perenniporia tephropora) and the brown-rot fungus (Coniophora olivacea) were found. Analysis of NIR spectra indicated that this relationship is causal with shared bands for mass loss and extractive content models at 6650, 6017, 5265 and 4659 cm−1. Partial least squares regression (PLSR), supplemented with spectra normalisation and variable selection, allowed prediction of mass loss with a residual mean square error (RMSE) of 7.48 % and 5.76 % for the white-rot and brown-rot, respectively. This level of precision allowed the characterisation of a E. bosistoana resource which showed a range of mass loss from 0 to 60 %. Genetic control was found for mass loss by the white-rot ( h2 = 0.70 and 0.24) and the brown-rot ( h2 = 0.15 and 0.13) at two sites in New Zealand. The rankings were correlated between sites, with genetic correlations (Rg2) of 0.69 and 0.63 for white-rot and brown-rot, respectively, as well as to the predicted extractive content (0.82 to 0.92). However, the study indicated a significant site effect on the decay resistance of the E. bosistoana heartwood. In summary, this study has shown that the decay resistance could be assessed rapidly and efficiently using NIR technology for genetic selection.

Introduction

Wood is a biodegradable material. To ensure a long service life in unfavourable environments timber is often treated with toxic preservatives (NZS3640, 2003; Treu et al., 2019) creating hazardous waste (Townsend and Solo-Gabriele, 2006). However, the heartwood of some species is highly resistant against biodegradation, able to substitute preservative treated timber for in-ground or marine applications (AS5604, 2005; Scheffer and Morell, 1998). Unfortunately such highly naturally durable timber is not common and often sourced from unsustainably or illegally harvested tropical forests (Nellemann, 2012). As such resources are dwindling, there is an opportunity to sustainably grow naturally durable timber species in fast-growing, short-rotation plantations (Bhat et al., 2005; Bush et al., 2011; Dünisch et al., 2010; Stirling et al., 2015).

Eucalyptus bosistoana heartwood is listed as class 1 ground-durable, able to last more than 25 years in the ground according to the Australian Standard (AS5604, 2005) and has many other favorable properties such as fast growth (Poynton, 1979), some frost tolerance (Hamilton, 1983) and high stiffness (Bootle, 2005). E. bosistoana has been chosen by the New Zealand Dryland Forests Initiative (NZDFI) to establish a sustainable plantation resource of naturally durable timber to, in the first instance, supply posts for agricultural industries (Millen et al., 2018).

The natural durability of heartwood is variable, both within (Sherrard and Kurth, 1933) and between trees (Bush et al., 2011; Hillis, 1987). Durability standards, which have been developed largely for old-growth native forest resources, recommend the use of the generally better performing outer heartwood of mature trees (AS5604, 2005). Therefore, good resistance to biodegradation of the timber, which is grown in short-rotation plantations needs to be ensured. A breeding programme can ensure quality, as the variation in decay resistance between individual trees of a species is partially under genetic control (Bush et al., 2011; Harju and Venalainen, 2002; Yu et al., 2003).

A major impediment for the inclusion of natural durability into tree breeding programmes, which rely on large sample numbers, is the laborious and time consuming nature of the available methods for assessing durability (AWPC, 2007). While field tests are not only affected by environmental factors such as soil, temperature and rainfall, they also, in particular for class 1 durable timber which needs to last more than 25 years in ground, carry on for decades. Alternatively, accelerated laboratory tests can be used for screening, but suffer limited transferability to real-life conditions as they are specific to the limited number of organisms included in the test (Jacobs et al., 2019). Laboratory test results are more comparable between laboratories but still take several months to complete. Consequently, a rapid and efficient method for durability assessments is needed.

Apart from wood anatomy (Meyer-Veltrup et al., 2017), a key factor determining the natural durability of heartwood is the presence of secondary low molecular weight organic compounds, the so called extractives (Hawley et al., 1924; Rudman, 1964). Therefore in a first instance, the extractive content (EC) in heartwood may provide an indirect measure of relative decay resistance and therefore could be used as an alternative way to assess natural durability within species (Morris and Stirling, 2012). Again solvent extraction methods are costly and laborious, requiring thorough sample preparation (TAPPI, 2012) and hence are unsuitable when large tree breeding populations are concerned. However, Near Infrared Reflectance (NIR) spectra, contain information of the chemical composition of materials. NIR spectra are quickly acquired with affordable instrumentation from solid wood samples, reducing demand on sample preparation and measurement (Schimleck et al., 2005). NIR spectroscopy has been successfully used to accurately predict the EC in wood (Li and Altaner, 2018; Ribeiro da Silva et al., 2013; Schimleck et al., 2009) and subsequently employed in a tree breeding programme (Li et al., 2018).

NIR is also able to successfully predict non-chemical wood properties such as stiffness or density by multivariate statistical analysis (Tsuchikawa and Kobori, 2015). Not surprisingly some attempts were made with varying success to use the technology to predict fungal decay resistance directly rather than the correlated EC (Bush et al., 2011; Gierlinger et al., 2003; Jones et al., 2011).

The objectives of this study were: firstly to verify the current procedure of selecting E. bosistoana of high EC in a breeding programme to improve durability. Secondly use this dataset to determine how precisely mass loss by fungi can be predicted from NIR spectra and thirdly to explore the potential of applying the NIR calibrations for decay resistance to a tree breeding trial.

Section snippets

Materials

Origin of the 1765 E. bosistoana heartwood samples has been described in detail (Li and Altaner, 2018; Li et al., 2018). In brief, 41 open-pollinated E. bosistoana families were grown at two different sites in the South Island of New Zealand in 2010, including the Craven Road (Longitude: 173°56′, Latitude: 41°26′) and Martin (Longitude: 172°39′, Latitude: 43°11′) sites studied in detail here (Li et al., 2018). The sites were on alluvial soils and experienced an average annual rainfall of around

Decay tests of E. bosistoana heartwood

The ML data ranged from -0.3 % to 59.9 % with an average of 9.62 % for the white-rot fungus Perenniporia tephropora and from -0.50 % to 48.7 % with an average of 7.82 % for the brown-rot fungus Coniophora olivacea (Table 1). The extractive content of the heartwood in the trees was predicted by NIR (pEC) and varied from 0.63 % to 17.20 % with a mean of 7.68 %. Negative correlations between pEC and ML for white-rot (r = -0.32, P < 0.01) and brown-rot (r = -0.42, P < 0.01) were observed. Samples

Decay tests of E. bosistoana heartwood

A stratified sample from more than 1700 cores was used to obtain a broad range of pEC for the assessment of ML. The broad range in ML benefited the multivariate statistics used for NIR calibration (Martens and Næs, 1984). Large variation in ML by wood rots is commonly reported (AWPC, 2007; Brischke et al., 2013; Bush et al., 2011; Harju and Venäläinen, 2006; Jones et al., 2011). The higher ML by the white-rot (P = 0.013) indicated that it is a bigger threat to E. bosistoana heartwood and a more

Conclusion

Fungal decay tests validated that on average the resistance of E. bosistoana heartwood against wood decay increased with pEC. This confirmed that the use of a quick assessment of extractive content as a proxy measurement for natural durability, which is currently used in a commercial E. bosistoana breeding programme (Li et al., 2018; Millen et al., 2018), should result in a more durable resource.

Further, it was possible to predict mass loss of E. bosistoana heartwood from NIR spectra combined

CRediT authorship contribution statement

Yanjie Li: Visualization, Methodology, Formal analysis, Writing - original draft. Monika Sharma: Data curation, Writing - review & editing. Clemens Altaner: Visualization, Methodology, Formal analysis, Writing - original draft. Laurie J. Cookson: Methodology, Investigation, Writing - review & editing.

Declaration of Competing Interest

The authors declare no conflicts of interest.

Acknowledgments

The authors gratefully acknowledge the funding from New Zealand's Ministry of Business, Innovation and Employment (MBIE) Partnership for Speciality Wood Products (contract FFRX1501). We would like to thank NZDFI for access to trials and data and Meike Holzenkämfer for technical assistance.

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