Developing Sustainable Wood Preservatives: The Antifungal Efficiency of Afzelia quanzensis Welv. and Androstachys johnsonii Prain Sawdust Extracts from Mozambique

This study aimed to both develop and assess the antifungal efficacy of extractives derived from different sets of sawdust originating from two hardwood species, namely chanfuta (Afzelia quanzensis Welv.) and mecrusse (Androstachys johnsonnii Prain). These hardwood species possess inherent characteristics of high natural durability. The primary objective was to use these extractives to impregnate perishable wood species, enhancing their durability and augmenting their commercial value. Collected wood sawdust was initially sieved to remove residues and unwanted materials and conditioned until 12% moisture content. Subsequently, the sawdust was Soxhlet-extracted using a mixture of organic solvents, including acetone, ethanol, and toluene. After evaporating the solvents, the resulting extractives were used to prepare a preservative solution with ethanol and acetone. The extractive solutions from each wood species were mixed with malt extract agar and then diluted to various concentrations: 0.125 mg/mL, 0.25 mg/mL, 0.5 mg/mL, 1.25 mg/mL, 2.0 mg/mL, and 2.5 mg/mL. For each concentration, fungal plugs from the periphery of actively growing cultures were moved to the centre of Petri dishes and placed in controlled laboratory conditions for incubation. The antifungal efficacy was assessed against specific wood-decaying fungi, including brown rot fungi (Coniophora puteana, Postia placenta, Lentinus lapideus) and white rot (Trametes versicolor). The evaluation involved daily monitoring of the linear expansion along two perpendicular radii for each fungus expressed as a percentage of the empty Petri dish area. The results indicated that the chanfuta extractives inhibited the growth of brown rot fungi at a concentration of 0.25 mg/mL and white rot fungi at 2.0 mg/mL. Similarly, the mecrusse extractives inhibit brown rot at 0.5 mg/mL and white rot at 2.0 mg/mL. The fatty acids Oleic (C18:1) present in the chanfuta extractives solution and linoleic (C18:2) in mecrusse extractives contributed to restraining the fungal growth. These results suggest that sawdust extractives from both wood species exhibit promising potential for creating environmentally friendly wood preservatives, which, with effective treatments, could extend the lifespan of perishable wood species