Biochemical characterization of wood decay and metabolization of phenolic compounds by causal fungi of grapevine trunk diseases

Authors: Galarneau, Erin; Wallis, Christopher; Baumgartner, Kendra

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2025
Publication Date: 4/16/2025
Citation: Galarneau, E.R., Wallis, C.M., Baumgartner, K. 2025. Biochemical characterization of wood decay and metabolization of phenolic compounds by causal fungi of grapevine trunk diseases. PLOS ONE. 20(4). Article e0315412. https://doi.org/10.1371/journal.pone.0315412.
DOI: https://doi.org/10.1371/journal.pone.0315412

Interpretive Summary: Grapevine trunk diseases, including Esca, Botryosphaeria dieback, and Eutypa dieback, are caused by a diverse range of fungi, which colonize the wood and cause internal lesions extending to the core of the wood, among other disease symptoms. The pathogens colonize the wood at different rates, which may, in part, reflect their abilities to decay the wood as a source of nutrition. Such variation in colonization, however, may instead reflect the pathogens’ tolerance of secondary metabolites (namely phenolic compounds) produced by the host in response to infection. To quantify their wood-decay abilities in vitro, Eutypa lata (Eutypa dieback), Fomitiporia polymorpha (Esca), and Diplodia seriata and Neofusicoccum parvum (weakly-virulent and highly-virulent Botryosphaeria-dieback pathogens, respectively) were inoculated to autoclaved wood blocks of Vitis vinifera ‘Merlot’ for six months. To determine cell wall-degrading enzyme activity in vitro, isolates were grown on minimal media amended with starch, pectin, lignin, cellulose, hemicellulose, tannic acid, gallic acid, and grapevine wood powder. To determine tolerance of and ability to metabolize phenolic compounds in vitro, isolates were grown in media amended with piceid, rutin, epicatechin, and gallic acid. Weight loss of autoclaved wood blocks inoculated with D. seriata was the greatest, whereas that of F. polymorpha was the least, although the latter decayed significant amounts of pectin and hemicellulose. Polyphenol-oxidase activity of E. lata in vitro with wood powder was 100-times higher than those of F. polymorpha, D. seriata, and N. parvum. N. parvum was not impeded by phenolic compounds; it eliminated three of the four phenolics from the media, which may help explain why lesions during N. parvum infection develop faster than those of D. seriata, E. lata, and F. polymorpha.

Technical Abstract: Grapevine trunk diseases, including Esca, Botryosphaeria dieback, and Eutypa dieback, are caused by multiple Ascomycota and Basidiomycota fungi, which colonize the wood and cause internal lesions extending to the core of the wood, among other disease symptoms. The pathogens vary in the rate of lesion formation (a measure of virulence), which may, in part, reflect their abilities to utilize the main components of wood as nutritive substrates. Such variation in virulence may instead reflect the pathogens’ tolerance of secondary metabolites (namely phenolic compounds) produced by the host in response to infection. To quantify their wood-decay abilities in vitro, Eutypa lata (Eutypa dieback), Fomitiporia polymorpha (Esca), and Diplodia seriata and Neofusicoccum parvum (weakly-virulent and highly-virulent Botryosphaeria-dieback pathogens, respectively) were inoculated to autoclaved wood blocks of Vitis vinifera ‘Merlot’ for six months. To determine cell wall-degrading enzyme activity in vitro, isolates were grown on minimal media amended with starch, pectin, lignin, cellulose, hemicellulose, tannic acid, gallic acid, and grapevine wood powder. To determine tolerance of and ability to metabolize phenolic compounds in vitro, isolates were grown in media amended with piceid, rutin, epicatechin, and gallic acid. Weight loss of autoclaved wood blocks inoculated with D. seriata was the greatest, whereas that of F. polymorpha was the least, although the latter decayed significant amounts of pectin and hemicellulose. Polyphenol-oxidase activity of E. lata in vitro with wood powder was 100-times higher than those of F. polymorpha, D. seriata, and N. parvum. N. parvum was not impeded by phenolic compounds; it eliminated three of the four phenolics from the media, which may help explain why lesions during N. parvum infection develop faster than those of D. seriata, E. lata, and F. polymorpha.