Tree age is one of the most important factors to affect the natural durability of wood. To meet the industrial demand, recently, trees harvested at relatively young ages are increasing. Unfortunately, research data on short-rotation grown teak are very limited. In another case, black streak discolorations in the heartwood of teak may lead to considerable economic loss. The purposes of this study were to determine the natural termite resistance of heartwood and sapwood of teak for trees aged 8, 30 and 51 years, and to determine color and chemical characteristics of black streaked heartwood of teak.

　In chapter 2, Reticulitermes speratus Kolbe was employed as a test termite using a no-choice feeding method during a 14-day observation. The content of the extractives by successive extraction and the color of the wood (CIELAB system) were also determined. The survival rate and mass loss levels of sapwood and heartwood of 8-year-old trees are significantly higher than those of 30 and 51-year-old trees. The survival rate and mass loss levels in the heartwood regions of 30 and 51-year-old trees are not statistically different. The survival rate in the first week is moderately correlated to brightness, and redness of the wood. The mass loss is moderately correlated to n-hexane extractive content, total extractive content, brightness, and redness of the wood. This fact indicated that color properties could be a good indicator of termite resistance characteristics.

　Quinones are primarily responsible for the natural durability of teak. In chapter 3, thus, the radial distribution of quinones (tectoquinone, lapachol, desoxylapachol and its isomer) and other components in the different tree ages were identified and measured by means of GLC and GC-MS. With the exception of tectoquinone, significant lower amounts of quinones were found in the outer heartwood of 8 year-old trees compared to those of 30- and 51-year old trees, as well as between the inner and outer parts of the heartwood. The amount of tectoquinone and isodesoxylapachol in the sapwood and heartwood significantly correlated with natural termite resistance properties.

　A comparison was made of color and chemical differences between black streaked heartwood and normal heartwood in teak (chapter 4). The variously black streaked disks were grouped into two types by visual inspection and brightness (L*) value measurement: strong and thin streaked heartwood. The black streak part was less than 12-15 units in brightness value than the normal heartwood. The pH and calcium levels of the black streak part were slightly higher than that of normal wood. Furthermore, this portion gave appreciably higher n-hexane and ethyl acetate extractive contents compared to those in normal wood. Chemical analyses of the black streak heartwood showed similar identified compounds (tectoquinone, lapachol, desoxylapachol and its isomer) to that of normal heartwood, however, 2-tert-buthyl-anthraquinone and some unidentified peaks were found. The black streak heartwood contained significantly higher tectoquinone content. The brightness was moderately correlated to pH value and tectoquinone content in Pearson's correlation. Strong degrees of correlation were found between the brightness and ethyl acetate extractive content.

　In order to investigate the cause of discoloration, it is expected to identify the extractives contributing to the discoloration and to understand their conversion mechanism (chapter 5). The ethyl acetate extract of black streak parts was chromatographed on a silica gel column. Further, tectol, and two unidentified compounds (C-1 and C-2) were isolated. To test their significance to discoloration, those compounds and identified compounds in the heartwood were exposed in the air and treated with different pH. Tectol, C-1, and C-2 changed their color after those treatments. Tectoquinone and other anthraquinones were relatively stable at low and high pH, as well as in air-oxidation. It is obvious that tectol, could be one of the precursors to cause the blackening of the heartwood.

　In conclusions, in the heartwood of the 30-year-old trees revealed the same termite resistance level compared to that of 51-year-old trees. This is an encouraging result considering the recent increase of young trees utilization. With regard to discolored heartwood, tectol was observed to provide dark color after air oxidation. This fact suggests that a naphtaquinone dimeric structure could be involved to the development of black streak parts in teak wood.

（和訳）

　樹齢は木材の耐久性に影響を及ぼす重要な要因の一つである． 近年，チーク材需要の拡大により，比較的若い樹齢の木材が収穫されるようになってきている． しかし，この様な短伐期で生産されたチーク材の耐久性に関する研究は少ないのが現状である． 一方でこの様な比較的若いチークの心材にはよく縞状の変色が見られ，これもチーク材の価格を低下させている原因となっている．

　本研究は，植林されたチーク(８年生，30年生，51年生)を対象にそれぞれの抗蟻活性の比較と心材の変色機構の解明を目的として実施された。

　第２章では，ヤマトシロアリ( Reticulitermes speratus Kolbe)を用いた14日間の抗蟻活性試験を行い， 逐次抽出物及び材色との関係を検討した． シロアリの生存率と摂食量は辺材と心材いずれにおいても８年生で30年生や51年生のチーク材よりも明らかな増加が認められ， 30年生と51年生を比較すると大きな違いが認められなかった． 生存率(１週間目)は明度と赤味に相関が認められ，摂食量はヘキサン抽出物量，全抽出物量，明度，赤味に相関が認められた． これらのことからこれらの要因は耐久性の判断の指標となりうることが示唆された．

　第３章では，キノン類がチークの耐久性に主に寄与していると考えられることから， 異なる樹齢(８年生，30年生，51年生)における半径方向のキノン類をGC及びGC-MSを用いて分析した． その結果，tectoquinone, lapachol, desoxylapachol, isodesoxylapacolが確認された． また，樹齢との関係ではこれらの成分はtectoquinoneを除いて心材では８年生が少なく，30年生，51年生では多くなっており， 抗蟻活性試験の結果と一致していた． なお，辺材を含めてキノン類との相関をみるとtectoquinoneとisodesoxylapacolの含有量と抗蟻活性には著しい相関が認められた．

　第四章では，チーク材の変色心材と正常心材の材色と成分の相違について検討した． 変色心材は目視と明度により濃色と淡色に区別した． 変色心材の明度は正常心材より12-15程度低下し，pH，カルシウム含有量，ヘキサン抽出物量，酢酸エチル抽出物量が増加していた． 変色心材のキノン類はtectoquinone, lapachol, desoxylapachol, isodesoxylapacolの正常心材で確認されたもの以外にも 2-tert-buthyl-anthraquinoneが確認された。 それらの含有量は変色材が多い傾向を示した． また，正常心材にはみられないいくつかの成分が変色材で確認された． 変色の程度を示す明度についてはpH値，tectoquinoneなどと相関を示し，酢酸エチル抽出物とは高い逆の相関を示した。

　第５章では，変色の原因成分について検討した． 明度と高い逆の相関を示した酢酸エチル抽出物から成分の単離を行った． その結果，２つの未確認物質とナフトキノン２量体のtectolが単離された． これらの化合物と正常心材で確認されたキノン類の着色試験(自動酸化，酸・アルカリ処理)を行ったところ， 単離３成分はいずれかの処理で着色することが確認された． 特に，tectolの着色は著しいものであった． 一方，tectoquinoneなどのキノン類のほとんどはこれらの処理により濃色化しなかった． したがって，tectolなどの今回単離された成分は変色に関与する前駆体の一つと考えられた．

　以上の結果から，植林されたチーク材の耐久性は30年生と51年生で同じであることが判明した． このことはチーク材の利用にとって有益な結論を得たものと考えられた． また，チーク材の変色についてはtectolのような２量体の関与を示唆する新たな知見を得ることができた．