Tree could produce varies types of wood timber for industry and society use, among these, one of the most valuable and popular type of wood, especially in China, is the natural durable wood with splendid colours. Wood which has natural durability could protect the wood against to biological decay [1, 2]. On the other hand, different colours wood, for instance, yellow or red, could potentially increase the value of the wood for end use. Therefore, natural durability wood with colour have been widely studied. In tree stem, the inner part of wood is call heartwood, and the outside of wood is recognized as sapwood, with the growth of tree, cells in the inner part of sapwood began to die and accumulated massive secondary metabolites, this process are transfer the sapwood into heartwood with natural durability and colourful . However, the traditional methods to test the wood natural durability are costly and time-consuming. It has been reported that the extractives in the heartwood plays an important role for colourful and natural durability . Decomposition and colourlessness will appear when the extractives are removed from durable wood . Therefore, the amount of extractive content (EC) in heartwood has been studied as a proxy for natural durability .
The EC in heartwood has large variation and could be reduced by the genetic selection . There are different ways to determine the quantity of extractives in heartwood. The traditional methods such as Soxhlet or accelerated solvent extraction (ASE)  which are time- and cost- consuming could not suitable for tree breeding and selection programs, which rely on the measurement of large numbers of samples. A high throughput and rapid measurement method for EC is needed.
Near infrared spectroscopy (NIR) is a non-destructive technique that is used for the analysis of agricultural products [9-11]. It has been used to determine the quantity of heartwood extractives in some tree species [12-14] and yields a promising and reliable results. The NIR spectra that collected from different sample form, wood powder or solid, could influence the performance of wood traits prediction model.
The models that build on different size of milled wood powder are different and performed higher accuracy than the model based on the solid wood when predict the chemical properties in eucalyptus wood by NIR spectroscopy . However, wood sample grinding also a time consuming step and could reduce the extractive content prediction time, directly EC prediction from the solid wood samples could a suitable alterative way for NIR model calibration.
NIR spectra that take from the solid wood samples could influenced by many factors, such as moisture content  and grain angle . It has been reported that the grain angle could influence the EC prediction of Eucalyptus bosistoana using NIR spectra and this influence could be reduced by using of EPO algorithm . Alternatively, this influence may could reduced by using of feature selection methods. One of the most important feature selection method that has been reported that could remove confounding effects on NIR calibrations [18-20] is call significant Multivariate Correlation (sMC) . Feature selection combined with PLS method could found out the most important variables in NIR spectra when predicted the target chemicals content in plant and remove the irreverent variables that influenced the accuracy of the model prediction . However, The important features in the NIR spectra for the grain angles and EC are little known.
Toona sinensis is a native Chinese tree species that have been widely distribution in China, it has a long history of cultivation for its digestible buds in China. In addition, T. sinensis also hold the advantages of fast growth and bright red heartwood that has been widely used for furniture and industry use. It has been widely studied on many regions, including the cultivation, reproduction, and biological activity of T. sinensis and the physical characteristics and chemical of its wood. However, little is known about the nature duable and red colour timber. To establish an high quality breeding program for durable and red wood selection, it is need to find an alternative way to allow fast and efficient measure the heartwood quality of T. sinensis. If NIR can be successfully used to analyse the heartwood properties without any grain angle influence, the traditional methods which are time- and cost- consuming can be replaced and consequently, it will give a lot of benefit for selection.
Hence, This study will focus on the effect of grain angle on NIR spectra obtained from T. sinensis cores, and study the possibility of applying NIR as a rapid and precise method to predict the extractives content from the solid core samples of T. sinensis without grain angle.