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Fomitiporia mediterranea M. Fisch. (Fmed) is a basidiomycete first described in 2002, and was considered up to then as part of Fomitiporia punctata (P. Karst) Murrill. This fungus can degrade lignocellulosic biomass, causing white rot and leaving bleached fibrous host residues. In Europe Fmed is considered the main grapevine wood rot (Esca) agent within the Esca disease complex, which includes some of the most economically important Grapevine Trunk Diseases (GTDs). This review summarises and evaluates published research on Fmed, on white rot elimination by curettage or management by treatments with specific products applied to diseased grapevines, and on the relationship between wood symptoms and Grapevine Leaf Stripe Disease (GLSD) in the Esca disease complex. Information is also reviewed on the fungus biology, mechanisms of pathogenicity, and their possible relationships with external foliar symptoms of the Esca disease complex. Information on Fmed control strategies is also reviewed.

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Eutypa dieback and Esca complex are fungal diseases of grape that cause large economic losses in vineyards. These diseases require, or are enhanced by, fungal consortia growth which leads to the deterioration of the wood tissue in the grapevine trunk; however, pathogenesis and the underlying mechanisms involved in the woody tissue degradation are not understood. We examined the role that the consortia fungal metabolome may play the role in generating oxygen radicals that could potentially play a role in trunk decay and pathogenesis. Unique metabolites were isolated from the consortia fungi with some metabolites preferentially reducing iron whereas others were involved in redox cycling to generate hydrogen peroxide. Metabolite suites with different functions were produced when fungi were grown separately vs. when grown in consortia. Chelator-mediated Fenton (CMF) chemistry promoted by metabolites from these fungi allowed for the generation of highly reactive hydroxyl radicals. We hypothesize that this mechanism may be involved in pathogenicity in grapevine tissue as a causal mechanism associated with trunk wood deterioration/necrosis in these two diseases of grape.

The use of TiO2 nanoparticles for photoprotection comprise a side effect due to the photocatalysis of the nanoparticles under UV radiation. In this work we studied how the suppression of TiO2 photocatalytic activity may affect the production of phenoxy radicals and the color of wood surfaces exposed to UV radiation. The experimental work considered the modification of TiO2 nanoparticles to reduce its photoactivity and the use electron paramagnetic resonance to test free radical production. Wood samples were treated with the different TiO2 nanoparticles and the radical production and color changes were evaluated after UV exposure. Experimental results showed that in wood samples exposed to UV radiation the use of TiO2 with suppressed photoactivity yielded increased amounts of phenoxy radicals, in comparison to samples treated with photoactive TiO2. Similar results were obtained in terms of color change, where samples treated with suppressed photoactivity TiO2 showed significantly higher color changes values, after 2000 h of UV exposure, than samples treated with photoactive TiO2. These results suggest that in wood surfaces, the photocatalytic effect of TiO2 may be crucial on the performance of the nanoparticles as photoprotective treatment.

The chelator-mediated Fenton (CMF) chemistry is one of the main biological non-enzymatic systems for oxygen-centered radical generation. Perhydroxyl radical (HO2•) is a secondary radical specie in CMF systems, however, despite...

Eutypa dieback and Esca are serious grapevine trunk diseases (GTDs) caused by fungal consortia causing large economic losses in vineyards. Depending on the disease the species involved include Eutypa lata, Phaeoacremonium minimum, and Phaeomoniella chlamydospora. There is a need to understand the complex pathogenesis mechanisms used by these fungi to develop treatments for the diseases they cause. Low molecular weight metabolites (LMW) are known to be involved in non-enzymatic oxygen radical generation in fungal degradation of wood by some Basidiomycota species, and as part of our work to explore the basis for fungal consortia pathogenesis, LMW metabolite involvement by the causal GTD fungi was explored. The GTD fungal pathogens examined, E. lata, P. minimum and P. chlamydospora, were found to produce low molecular weight iron binding metabolites that preferentially reduced iron or redox cycled to produce hydrogen peroxide. Uniquely, different LMW metabolites isolated from the GTD fungi promoted distinct chemistries that are important in a type of non-enzymatic catalysis known as chelator-mediated Fenton (CMF) reactions. CMF chemistry promoted by LMW metabolites from these fungi allowed for the generation of highly reactive hydroxyl radicals under conditions promoted by the fungi. We hypothesize that this new reported mechanism may help to explain the necrosis of woody grapevine tissue as a causal mechanism important in pathogenesis in these two grapevine trunk diseases.

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