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Chemical composition, antitermite and antifungal activity of Dacryodes edulis oleoresin
2019 - IRG/WP 19-20653
Damages to wood structures and other cellulosic materials caused by wood destroying insects and fungi are estimated to several billions of dollars each year in the world. Among these, termites are considered as one of the most economically important pests for wooden structures. In the past, several wood protection chemicals like CCA, creosote, lindane or pentachlorophenol have been used. However, even if some of these products are still in use depending of the countries and of their own regulations, most of them have been largely limited in Europe (and Northern America or even banned because of their impact on the environment and the human health. Growing environmental pressures associated to the decrease of fossil resources has contributed to significant changes in the field of wood preservation leading to the research of more environmentally acceptable wood preservation solutions. In this context, products issued from renewable biomass present several advantages: they require less energy to be produced limiting carbon dioxide emissions, biodegradability of biomass make them generally less harmful to the environment. The use of natural products derived from renewable raw materials, replacing chemicals of petrochemical origin, is therefore of growing interest. Some wood species are naturally resistant to termites and fungi attacks, due to the presence of secondary metabolites produced by trees as natural defense system. Dacryodes edulis, also known as African plum tree (En) or Safoutier (Fr), occurs naturally in Gabon, where it is widely used for its fruits. Its wood is reported to present similar properties to African mahogany, but it is still mainly used as firewood, even if it is reported by local populations to be resistant to termites. The tree is also able to exudate oleoresin in response to different stress or injuries. Indeed, exudation is a natural mechanism that plants use to heal their wounds. In addition, some authors consider it to be a protection in response to mechanical lesions or microbial invasion. In this context, the aim of this study was to evaluate the properties of Dacryodes edulis oleoresin as potential anti-termite and fungicide agents to develop more acceptable wood protection systems based on used of bio-pesticides. For this purpose, essential oil was separated from oleoresin using steam distillation with a Clevenger apparatus, while oleoresin was purified using different solvents. Each fraction was analyzed using GC-MS and subjected to different biological tests to evaluate their anti-termite and fungicidal properties.
W F Bedounguindzi, K Candelier, P E Engonga, Se Dumarcay, M-F Thevenon, P Gerardin

Efficiency of three resin fractions from Aucoumea Klaineana Pierre, Canarium schweinfurthii Engl and Dacryodes edulis (G. Don) H. J. Lam from Gabon combined with Tebuconazole as wood preservatives
2022 - IRG/WP 22-10998
Pure resins from Aucoumea Klaineana, Canarium schweinfurthii and Dacryodes edulis were harvested and then hydro-distilled to obtain essential oils and purified resins fractions. Due to the potential leaching and volatility hazards of the compounds that constitute these fractions, resins and essential oils were combined with tebuconazole to produce both antifungal and anti-termite wood preservatives formulations. Beech and scots pine wood block samples were impregnated by these different formulations and expose to Trametes versicolor and Coniophora puteana, respectively. Treated and control scots pine samples were also expose to termite (Reticulitermes flavipes). The results indicate that the use of aqueous formulations of the three fractions of the different Gabonese wood species combined to tebuconazole improves the wood resistance against termites and Coniophora puteana. Currently, the promising protection obtained would be limited to indoor applications since the different formulations should be formulated to be resistant to leaching.
W F Bedounguindzi, K Candelier, P Edou Engonga, S Dumarcay, M-F Thevenon, P Gerardin

Invasion and colonisation of bamboo culm material by stain and decay fungi
2002 - IRG/WP 02-10453
Two distinct stages of the fungal infection of bamboo culms can be identified: entry into the culm itself (invasion) and further colonisation by spread within the culm wall tissue. This laboratory study aimed to characterise different invasion strategies of a variety of fungi. Well-known isolates of white- (Coriolus versicolor, Schizophyllum commune), brown- (Coniophora puteana, Gloeophyllum trabeum, Poria placenta), soft-rotting (Chaetomium globosum) and stain fungi (Lasiodiplodia theobromae) were used as test organisms in culm wall material of Moso Bamboo (Phyllostachys edulis). By giving the fungus defined “entrances” into the specimen and by introducing a “baiting” method, routes of entry taken by fungal hyphae during infection of the culm tissue were investigated using light and scanning electron microscopy. he results show clearly that typical bamboo decay fungi such as S. commune and C. globosum can infect the fresh, undamaged culms via the dense outer epidermis if growth conditions are optimal. No part of the culm was identified as a barrier. Small bore holes in the epidermis, caused by penetrating hyphae were identified using scanning electron microscopy. It is proposed that this was the main pathway of entry into the culm tissue.
G Kleist, I Morris, R J Murphy

Chemical compositions and anti-termite activities of essential oils from Gabonese Canarium schweinfurthii Engl, Dacryodes buettneri Engl and Aucoumea klaineana Pierre wood resins.
2017 - IRG/WP 17-10895
Essential oil extract from resins of Canarium schweinfurthii, Dacryodes buettneri and Aucoumea klaineana woods from Cap Esterias and Oyem areas, Gabon, were prepared by Clevenger - steam distillation. The chemical compositions of these respective essential oils were analyzed by a Gas Chromatography coupled with Mass Spectrometry (GC-MS). Although monoterpenes were the main constituents of the three essential oils, each wood resins had a various essential oil yield after steam distillation process [6,92% (A. klaineana), 4,20% (C. schweinfurthii) and 13,19% (D. buettneri)] and their respective chemical compositions were slightly different. It results that monoterpenes, as α –pinene, o-cymene, alpha-phellandrene and D-limonene form the major constituents of terpenoides and phenylpropanoïdes compounds which are the most active substances against termite activity. The anti-termite activities of the three essential oils were evaluated, performing no-choice tests. 70 μL of each essential oil diluted in acetone with mass ratios of 50:50 and 25:75 [essential oil: acetone] were impregnated on Whatman papers and exposed to termite (Reticulitermes flavipes). Essential oil from Canarium schweinfurthii resin showed the strongest inhibitory activity against the termite with 100% mortality after 1 day at 50:50 and 25:75 concentrations followed by Aucoumea klaineana resin with the 100% mortality after 3 days at 50:50 and 25:75 concentrations. Finally, essential oil from Dacryodes buettneri resin showed the lowest termite resistance with 48.34 % and 58.34% mortalities after 14 days at 50:50 and 25:75 concentrations, respectively. The number of chemical components from each essential oil and their respective quantity, determined by GC-MS, are related to their anti-termite activity level.
Chemical compositions and anti-termite activities of essential oils from Gabonese Canarium schweinfurthii Engl, Dacryodes buettneri Engl and Aucoumea klaineana Pierre wood resins.

Coula edulis baill an unknown wood species as an alternative to the main durable wood species used in Gabon
2019 - IRG/WP 19-10945
The Congo Basin hosts an exceptional biodiversity of trees, flora and fauna. However, the immense natural heritage of the forests in this area is increasingly threatened by many anthropogenic factors, due to selective exploitation of certain wood species. In Gabon, whose ecosystem is representative of this area, the forest represents nearly 80% of the national territory. Only a minority of wood species is exploited because of their high market value (Ageos, 2015). The direct consequences of this selective exploitation are the decrease of the disponibility and even the eventual disappearance of certain wood species associated to the fast-growing international tropical timber markets. This is the case for kevazingo, which is classified as an endangered species and therefore prohibited from exploitation. In addition to these main exploited species, several less known species are available in Gabon. This is the case of the Gabonese hazelnut tree (Coula edulis baill), whose wood is used by local populations for its longevity because of its resistance to fungi, insects and more particularly termites. It is used to make forge coal and is used in the construction of huts such as posts and lintels (Moupela C et al, 2010-2013). In this context, it seemed interesting to study more in detail this species, having for the moment been the subject of little scientific investigations. The aim of this study was to investigate the natural durability of Coula edulis and the reasons of this latter one based on wood chemical composition. For this purpose, durability tests were carried out in Petri dishes on native and extracted samples of heartwood towards brown rot (Poria placenta and Coniophora puteana) and white rot (Coriolus versicolor and Pycnoporus sanguineus) fungi showing that unextracted samples presented higher durability to fungi. Fungal growth inhibition tests carried out with different concentrations of extractives confirmed their important fungicidal effects. Percentage of the different wood polymers and chemical composition of wood extractives were evaluated to find correlation between durability and wood chemistry. Results indicated that natural durability of Coula edulis could be explained by several reasons like the high density and hydrophobicity of its wood as well as its high lignin and extractives contents. Chemical analysis performed on extractives by GC-MS indicated the presence of gallic acid, quercetin and tannins.
C S A Bopenga Bopenga, S Dumarçay, P Edou Engonga, P Gerardin