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The gradual elimination of chromium from wood preservative formulations results in higher Cu leaching and increased susceptibility to wood decay fungi. Finding a sustainable strategy in wood protection has become of great interest among researchers. The objective of these in vitro studies was to demonstrate the effect of T-720-enriched organic charcoal (biochar) against five wood decay basidiomycetes isolated from strongly damaged poles. For this purpose, the antagonistic potential of Trichoderma harzianum (strain T-720) was confirmed among other four Trichoderma spp. against five brown-rot basidiomycetes in dual culture tests. T-720 was genetically transformed and tagged with the green fluorescent protein (GFP) in order to study its antagonistic mechanism against wood decay basidiomycetes. It was also demonstrated that T-720 inhibits the oxalic acid production by basidiomycetes, a well-known mechanism used by brown-rot fungi to detoxify Cu from impregnated wood. Additionally, this study evaluated the effect of biochar, alone or in combination with T-720, on Cu leaching by different preservatives, pH stabilization and prevention of wood decay caused by five basidiomycetes. Addition of biochar resulted in a significant Cu binding released from impregnated wood specimens. T-720-enriched biochar showed a significant reduction of wood decay caused by four basidiomycetes. The addition of T-720-enriched biochar to the soil into which utility poles are placed may improve the efficiency of Cr-free wood preservatives.

The production of new generation of wood preservatives (without addition of a co-biocide) in combination with an exchange of wood poles on identical sites with high fungal inoculum, has resulted in an increase of premature failures of wood utility poles in the last decades. Wood destroying basidiomycetes inhabiting sites where poles have been installed, have developed resistance against wood preservatives. The objective of the in vitro studies was to identify a Trichoderma spp. with a highly antagonistic potential against wood destroying basidiomycetes that is capable of colonizing Cu-rich environments. For this purpose, the activity of five Trichoderma spp. on Cu-rich medium was evaluated according to its growth and sporulation rates. The influence of the selected Trichoderma spp. on wood colonization and degradation by five wood destroying basidiomycetes was quantitatively analyzed by means of dry weight loss of wood specimens. Furthermore, the preventative effect of the selected Trichoderma spp. in combination with four Cu-based preservatives was also examined by mass loss and histological changes in the wood specimens. Trichoderma harzianum (T-720) was considered the biocontrol agent with higher antagonistic potential to colonize Cu-rich environments (up to 0.1% CuSO4 amended medium). T. harzianum demonstrated significant preventative effect on wood specimens against four wood destroying basidiomycetes. The combined effect of T. harzianum and Cu-based wood preservatives demonstrated that after 9 months incubation with two wood destroying basidiomycetes, wood specimens treated with 3.8 kg m-3 copper-chromium had weight losses between 55-65%, whereas containers previously treated with T. harzianum had significantly lower weight losses (0-25%). Histological studies on one of the wood destroying basidiomycetes revealed typical decomposition of wood cells by brown-rot fungi in Cu-impregnated samples, that were notably absent in wood specimens previously exposed to T. harzianum. It is concluded that carefully selected Trichoderma isolates can be used for integrated wood protection against a range of wood destroying basidiomycetes and may have potential for integrated wood protection in the field.

Abstract: Laboratory and field tests were performed to establish the potential of Trichoderma spp. as a wound treatment for biological control of wood decay fungi in urban trees. A selection of Trichoderma species were tested in dual culture and interaction tests in wood against four basidomycetes Ganoderma adspersum, Ganoderma lipsiense, Inonotus hispidus, Polyporus squamosus and one acomycete Kretzschmaria deusta. Hyphal interactions were observed by scanning electron microscopy (SEM). The effect of Trichoderma spp. on wood colonization and degradation of wood decay fungi were quantitatively measured by dry weight loss of wood and qualitatively by histological studies. Trichoderma atroviride (T-15603.1) was consistently and highly competitive against most wood decay fungi with the exception of Polyporus squamosus which showed resistance towards antagonism in laboratory tests. Field experiments with T-15603.1 were carried out at different locations and hosts. A total of 159 angiosperm trees and 1431 wounds from six different species (Platanus × hispanica, Acer pseudoplatanus, Tilia platyphyllos, Populus nigra, Quercus rubra, Robinia pseudoacacia) were treated with different conidial suspensions. In comparison to control wounds, T-15603.1 induced a highly significant (P <0.001) preventive effect (82.3%) against the selected wood decay fungi. Monitoring results with RAPD-PCR showed that the conidial formulation of 0.1% urea and 0.2% glucose combined with a humidity storing gel as a carrier substance enhanced significantly (P <0.001) the germination rate, conidial viability and therefore the establishment of T-15603.1 in the wood substrate. The results demonstrate that T-15603.1 can be successful following application as biological wound treatment against wood decay fungi on urban sites. [Copyright &y& Elsevier]