Enzymatic Activities, Characteristics of Wood-Decay and Wood Substrate Specificity within Genera of Some Wood-Rotting Basidiomycetes from Cameroon and Tropical Africa

Abstract

A total of 72 species of wood-rotting Basidiomycetes belonging to 40 genera, 13 families and 5 orders, were investigated in this study of which 46 for the first time as far as type of wood-rot is concerned. 61 of the 72 cause white rot (W) representing 84.72 % of the total and 11 cause brown rot (B) or just 15.27 %, confirming the predominance already known of white rot (W) on brown rot (B) as shown in other studies. Results recorded show that even though most species belonging to same genera display the same type of rot (W or B), species of some few other genera were found to rather display different types of rot (W and B) in species within the same genera. Other results show that when determining the type of wood-rot caused by some species of fungi, in case of negative (-) test using tincture of guaiac which is known as the key test to determine the type of rot, syringaldazine must also be used as a differential test before concluding whether the species is a white (W) or brown rot (B) fungus. The level of activity of tyrosinase and peroxidase shows important variations between species of some genera, whereby some species of a given genus show varying potential level (+, ++, +++, ++++) of activities of these two enzymes, whereas other species of the same genus show no sign (-) of activity of the same enzymes. Therefore, our results led to the conclusion that the presence (+, ++, +++, ++++) or absence (-) of activity of peroxidase and tyrosinase can from now onwards also be used as an enzyme linked taxonomic criteria to distinguish between species of some genera. About detection of laccases activity, if a negative (-) result occurs during detection test in a wood-rotting fungus using syringaldazine, α-naphtol must also be used as a differential test before concluding on whether the species produces laccases or not. Based on the overall results recorded in the detection of enzymes activities, it appears necessary to use, where indicated, several substrates with different chemical sensitivities to detect the existence of an enzyme and its potential activity level in a fungal species. Additionally, preliminary lists of wood-decay fungi with potentially strong (+++, ++++) capacity to produce different types of polyphenol oxidases potentially usable in paper making industries, wastewater treatment and soil remediation, are provided. With regard to the study of substrate specificity which aimed at finding out the existence or not of a specificity between polyporales and tree wood species on which they grow, the first results recorded on a limited number of trees investigated led to the preliminary conclusion that, although some few tree species may serve as hosts for only a single species of polyporales, there is rather a greater tendency of finding several species growing on different species of wood as well as the same species of wood hosting several species of polyporales. These field observations led to the remark that a much larger inventory including a greater number of tree species in various tropical ecosystems is necessary in order to come out with a final conclusion.