Effect of intensity of gravitational stimulus artificially induced on growth and formation of tension wood in young shoots of poplar (P. euramericana cv. Ghoy).

La formation d'un tissu de bois de tension est induite artificiellement au moyen d’un stimulus gravitationnel obtenu en inclinant de jeunes pousses de l’année de Peuplier euraméricain cv ‘Ghoy’ à diverses intensités de 0 à 30° durant la saison de végétation. Au terme de l’expérimentation, il s’avère que l’allongement des pousses ainsi que l’angle de l’arc de bois de tension, ne sont pas affectés par l’intensité du stimulus. Au contraire, le redressement de l’axe, la quantité de fibres gélatineuses, la croissance secondaire sur écorce, la surface de la section et du xylème secondaire, les différents rayons caractéristiques, les diamètres sous écorce et l’excentricité de la moelle, répondent quantitativement à l’inclinaison. La quantité de bois de tension est corrélée au redressement, à la croissance secondaire sur écorce et à la croissance radiale sous écorce. Par ailleurs, la formation du bois de tension et l’excentricité réagissent au stimulus gravitationnel, sans pour autant être liés entre eux par une relation de cause à effet. Enfin, il existe une position naturelle d’équilibre des tiges, différente de la verticale, vers laquelle les pousses qui ont été déplacées, tentent de revenir en formant un tissu de bois de tension.The formation of tension wood tissue is artificially induced by means of a gravitational stimulus obtained by inclining young shoots of poplar at different intensities, from 0 to 30°, during a growing season. At the end of the experiment, it appears that shoot elongation as well as the angle of tension wood arc are not affected by the stimulus intensity. In contrast, the upright reorientation of the axis, the amount of gelatinous fibres, the secondary growth over bark, the cross-section area of the stem and of the secondary xylem, the different rays, the diameter under bark and the pith eccentricity, react quantitatively to the lean intensity. The amount of tension wood is correlated with the upright reorientation, the secondary growth over bark and the radial growth under bark. Tension wood formation and eccentricity react to the gravitational stimulus but they are not causally linked. Finally, it exists a natural equilibrium position, different from the vertical, to which moved shoots try to return via the formation of a tension wood tissue

Characterization of black locust (Robinia pseudoacacia L.) heartwood extractives : identification of resveratrol and piceatannol.

Robinia pseudoacacia L. heartwood is characterized by a very high natural durability. However, a significant difference was observed between the mature and juvenile heartwood, the latter presenting less durability against fungi decay, which could be attributed to lower extractive content. In order to elucidate this idea, extractives from mature and juvenile heartwoods of black locust trees were investigated. Results showed that extractive and phenolic contents were higher in mature than in juvenile heartwoods. The identification of phenolic compounds by UPLC–DAD–MS/MS revealed, for the first time, the presence of resveratrol and piceatannol. These two stilbenes as well as the flavonoid dihydrorobinetin were present at the highest level in mature heartwood, and as they are known antifungals, they could account for the great durability of mature heartwood. The stilbenes were detected in significant amounts particularly in mature heartwood where piceatannol reached a level tenfold higher than that reported for Japanese knotweed roots, the primary natural source of these stilbenes, whereas resveratrol level was comparable with reported values. As resveratrol and piceatannol receive increasing demand for nutraceutical, cosmetic and, possibly, pharmaceutical purposes, due to their beneficial health effects, this study underlines the use of R. pseudoacacia as a promising sustainable and economical source of resveratrol and piceatannol.WALEXTRAC

Characterization of <i>Fomes fomentarius s.s. and F. inzengae</i> in Belgian Beech Forests

Real-time PCRs were developed to characterize Fomes fomentarius lineages occurring in the beech forests of the Ardennes (southern Belgium). A collection of F. fomentarius sensu lato isolates was built up in 2020 and 2021 from basidiocarps developing on beech trunks, stumps, or logs. Two of the 148 isolates tested (monokaryotic and dikaryotic) belonged to the species Fomes inzengae, while the other isolates corresponded to the species Fomes fomentarius sensu stricto. As far as we know, this is the first record of Fomes inzengae in Belgium. This fungus was also found in a mature tree not showing any signs of decay. This demonstrates its endophytic nature. Growth tests at different temperatures, as well as wood degradation tests in accordance with standard NBN EN113 showed different behavior between both species. Passive sticky traps were installed during two growing seasons at the two sites where F. inzengae had been reported. Spores were detected at all collection times between April and July, using the specific molecular test developed. Moreover, in 2023, the DNA concentrations measured were 100 times higher than in 2022. The implications of this new species in Belgium is discussed in the context of climate change