Scots pine (Pinus sylvestris L.) wood is desired in woodworking industries due to its favorable timber characteristics and natural durability that is contributed by heartwood extractives. It has been discussed whether the Scots pine heartwood extractives (mainly stilbenes and resin acids) are synthesized in the cells of the transition zone between sapwood and heartwood, or if they are transported from the sapwood. Timing of heartwood formation during the yearly cycle has also not been unambiguously defined. We measured steady-state mRNA levels in Scots pine transition zone and sapwood using RNA sequencing. Year-round expression profiles of selected transcripts were further investigated by quantitative RT-PCR. Differentially accumulating transcripts suggest that, of the Scots pine heartwood extractives, stilbenes are synthesized in situ in the transition zone and gain their carbon-skeletons from Suc and triglycerides. Resin acids, on the other hand, are synthesized early in the spring mainly in the sapwood, meaning that they must be transported to the heartwood transition zone. Heartwood formation is marked by programmed cell death that occurs during the summer months in the transition zone.
To exploit the variation in the natural durability of heartwood timber, screening of a large number of trees or timber is necessary. We suggest that the concentration of total phenolics, measured by the Folin–Ciocalteu (FC) assay, can be used to supplement or even replace in vitro decay tests for screening the variation in the resistance of Scots pine (Pinus sylvestris L.) heartwood timber against the brown-rot fungus Coniophora puteana (Schum. ex Fr.). We screened the juvenile heartwood of 520 Scots pine trees with the FC assay. Samples from 40 trees, with total phenolics concentrations ranging from 1.9 to 21.7 mg tannic acid equivalents (TAE)/g of heartwood, were subjected to an in vitro decay test. The correlation (r) between the total phenolics concentration and mass loss was –0.82 (p < 0.001) in the 7 week long decay test. The relationship was expressed with a linear regression equation: mass loss (mg/g) = 487 – 25 × concentration of total phenolics (mg TAE/g). This strong relationship could be exploited by replacing the decay test with the FC assay to more rapidly assess the durability of wood products.
In this greenhouse experiment, 3-year-old Scots pine (Pinus sylvestris L.) seedlings were wounded by drilling holes through the stem. In the xylem next to the wound, the concentration of resin acids (RAC) increased, and the production of extractives typical for heartwood (stilbenes) and knotwood (stilbenes and lignans) of mature trees was induced. The induced stilbenes were pinosylvin (PS) and pinosylvin monomethyl ether (PSM), and the lignans nortrachelogenin (NTG) and matairesinol (MR). There was positive phenotypic correlation between concentrations of the different extractives. Except for the RAC, the extractive concentrations showed no correlation with the size of the seedlings. The treated seedlings belonged to half-sib families, which enabled the estimation of the genetic parameters for the response variables. The proportion of heritable variation (heritability, h(2)) in the concentration of PS, NTG and MR varied between 0.71 and 1.03, whereas for PSM and RAC the heritability was lower (0.35 and 0.31). Genetic correlation was significant between PS and PSM (r = 0.55, P = 0.018), and between NTG and MR (r = 0.50, P = 0.033). Heritabilities were also estimated on the basis of the regression of the offspring on their mothers h(2)(0P). These estimates were assessed for the concentration of PS, PSM and RAC in the wound response area of the seedlings and correspondingly in the heartwood of their mothers. The heritability was highest for the concentration of PS h(2)(0P). The findings of this study support the suggestion that the wounding of Scots pine seedlings may facilitate the development of an early testing method for breeding heartwood durability.
Stilbenes are abundant in the heartwood of Scots pine (Pinus sylvestris L.) and are known to have strong antifungal efficiency. In this study, Scots pine sapwood blocks were impregnated with crude heartwood extract containing the stilbenes pinosylvin (PS) and the pinosylvin monomethyl ether (PSM). Impregnated blocks were submitted to brown-rot fungi, Coniophora puteana, Gloeophyllum trabeum, and Rhodonia (Poria) placenta, and fungal growth test and decay test were performed. Both tests showed that the impregnation with a high concentration of stilbenes (60 mg g-1 dry wood) significantly suppressed the growth of fungi and slowed down the decay process of wood blocks, especially in case of G. trabeum. However, chemical analysis showed that PS and PSM were degraded by all the three types of fungi, obviously via modification to resveratrol and methylresveratrol. Rhodonia placenta displayed the fastest rate of degradation. Thus, impregnation with biodegradable stilbenes could be a viable alternative for wood preservation only in service situations with low or transient risk of decay.
-The importance of factors contributing to the natural decay resistance of Scots pine wood was studied. The decay rate of sapwood and outer and inner heartwood of 16 ca. 170-year-old Scots pines was first measured. A six-week decay test was performed with 5´15´30 mm wood blocks in dishes containing a brown-rot fungus (Coniophora puteana). The average mass loss in sapwood was 141 mg/cm 3 , in outer heartwood 57 and in inner heartwood 108. The variation between trees was largest in outer heartwood. The corresponding basic densities were 439, 456 and 411 mg/cm 3 . The mass loss was then compared with chemical characteristics and the sorption of water by parallel sample blocks in order to determine which factor has the greatest effect on decay resistance. The differences in heartwood mass loss were explained best by the concentration of pinosylvin and its monomethyl ether, which are phenolics belonging to the group of stilbenes, as well as by the concentration of total phenolics determined by the Folin-Ciocalteu method.decay resistance / heartwood / phenolic compound / pinosylvin / resin acid / moisture content Résumé -Variation de la résistance à la pourriture et relation avec les autres caractéristiques du bois dans les vieux pins sylvestres. L'étude a porté sur l'importance relative des facteurs à l'origine de la résistance naturelle à la pourriture du pin sylvestre (Pinus sylvestris). Pour commencer, la vitesse de pourriture a été mesurée dans l'aubier et les parties externes et internes du duramen de 16 pins d'environ 170 ans. Un test de pourriture de six semaines a été effectué sur des blocs de 5´15´30 mm dans des boîtes de Petri, dans lesquelles le champignon lignivore de la pourriture brune (Coniophora puteana) se développait sur une base d'extrait de malt gélosé. Les pertes de poids de l'aubier, de la partie externe du duramen et de la partie interne du duramen ont été de 141, 57 et 108 mg/cm 3 , respectivement. La variation entre les arbres était la plus grande dans la partie superficielle du duramen. Les densités du bois correspondantes étaient de 439, 456 et 411 mg/cm 3 . Ensuite, les pertes de poids, les caractéristiques chimiques des blocs adjacents et la quantité d'eau absorbée par ces derniers ont été comparées, dans le but de déterminer les facteurs affectant le plus la résistance à la pourriture du bois. Ce sont la teneur en composés phénoliques, en pinosylvine et éther mono-méthylique de cette dernière, faisant partie du groupe des stilbènes, et la teneur en phénols totale déterminée par le réactif de Folin-Ciocalteu qui expliquent le mieux les différences de pertes de poids du duramen. Les différences s'expliquent aussi dans une certaine mesure par le taux d'humidité du bois atteint dans une humidité élevée (HR de 100 %). Une corrélation significative existait entre la quantité de stilbènes et la quantité d'eau absorbée par le bois immergé dans l'eau. résistance à la pourriture / duramen / composés phénoliques / pinosylvine / acides résiniques / taux d'humidité
The cell wall chemistry (amount of hemicellulose, a-cellulose, and total lignin) and the concentration of extractives (total acetone-soluble extractives, resin acids, pinosylvins and the total phenolics quantified as tannin acid equivalents) were studied in brown-rot resistant and susceptible juvenile heartwood of Scots pine (Pinus sylvestris L.). The study material consisted of a total of 18 trees from two 34-year-old progeny trials at Korpilahti and Kerimäki. The trees were selected from among 783 trees whose decay rate had previously been screened in a laboratory test using a brown-rot fungus, Coniophora puteana. Samples from neither location showed any significant difference in the concentration (mg/cm 3 ) of hemicellulose, a-cellulose and total lignin between the decay resistant and susceptible trees. At both locations only the concentration of total phenolics was higher in the decay-resistant heartwood than in the decaysusceptible heartwood. At Korpilahti, the amount of acetone-soluble extractives and the concentration of pinosylvin and its derivatives were higher in the resistant than in the susceptible trees.
In the last decades, many wood preservatives have been prohibited for their ecotoxicity. The present article is focusing on the conifer-derived condensed tannins as environment-friendly options for the substitution of artificial wood preservatives. Eight different tannin fractions were extracted from spruce cones, spruce barks, and pine cones. The parameters of tannin extraction, such as the methods of purification and concentration of active components in the extracts, have been investigated. The cone and bark extracts were tested for the growth inhibition of eight brown-rot fungi, three white-rot fungi, and four soft-rot fungi in liquid cultures. The cone tannins provided a more efficient fungal growth inhibition than bark tannins. Purification increased the antifungal properties of the extracts. The growth of brown-rot fungi was inhibited by the tannins already at low concentrations. However, the extracts were not effective against the white-rot or soft-rot fungi. More investigation is needed concerning the tannin source and the purification procedure of the extracts before tannins can be considered as an ecologically benign wood preservative.
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