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Title: Various fungal communities colonise the functional wood tissues of old grapevines externally free from grapevine trunk disease symptoms

Author
item BRUEZ, EMILIE - Bordeaux Agro Sciences
item Baumgartner, Kendra
item BASTIEN, SYLVIE - Bordeaux Agro Sciences
item TRAVADON, RENAUD - University Of California
item GUERIN-DUBRANA, LUCIA - Bordeaux Agro Sciences
item REY, PATRICE - Bordeaux Agro Sciences

Submitted to: Australian Journal of Grape and Wine Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2015
Publication Date: 6/15/2016
Citation: Bruez, E., Baumgartner, K., Bastien, S., Travadon, R., Guerin-Dubrana, L., Rey, P. 2016. Various fungal communities colonise the functional wood tissues of old grapevines externally free from grapevine trunk disease symptoms. Australian Journal of Grape and Wine Research. 22:288-295.

Interpretive Summary: The grapevine trunk disease Esca tends to become more widespread as a vineyard ages. The percentage of diseased vines increases over time, as do yield losses for the whole vineyard. Nonetheless, leaf symptoms do not necessarily become more severe over time. In French vineyards, Esca leaf symptoms show a peak in severity in years 15 to 25, with a decline in years 30 to 50. To compare the relative abundance of different types of wood-colonizing fungi, we examined the apparently-healthy (functional) wood of ‘Baco blanc’, a hybrid grape produced for Armagnac in southwest France. The vines aged 42 and 58-years-old, from the same vineyard and showing no foliar symptoms of Esca or any other trunk disease, were sampled after uprooting. From the trunk of each vine, we cultured a total of 421 fungal species, and used a DNA-fingerprinting technique (Single-Stranded Conformational Polymorphisms, SSCPs) to compare fungal diversity between the vines of different ages. Multivariate statistical analyses showed that fungal community structure varied significantly between the two ages of vines. Many trunk pathogens, particularly the causal agents of Esca (42-year-old vines) and Eutypa dieback (58-year-old vines), were isolated. However, numerous mycoparasites (e.g., Trichoderma spp.) were also isolated. This decline in foliar symptoms among older vines may reflect an ‘equilibrium’ among trunk pathogens, mycoparasites, and saprobes.

Technical Abstract: The incidence of the trunk disease Esca tends to increase as a vineyard ages. Wood infections accumulate over time, as do yield losses. Nonetheless, symptom expression does not necessarily increase over time. In French vineyards, Esca foliar symptoms show a peak in severity in years 15 to 25, with a decline in years 30 to 50. To compare the relative abundance of different types of wood-colonizing fungi, we examined the non-necrotic wood of old plants of ‘Baco blanc’, a hybrid grape produced for Armagnac in southwest France. The vines aged 42 and 58-years-old, from the same vineyard and showing no foliar symptoms of Esca or any other trunk disease, were sampled after uprooting. From the trunk of each vine, we isolated a total of 421 fungal taxa, and used both the community of cultured fungi and Single-Stranded Conformational Polymorphisms (SSCPs) of the mt large subunit, amplified directly from non-necrotic wood, to compare fungal community structure among trunk locations (upper, central, basal) and between vine ages. Both canonical correspondence analysis (CCA) of cultured fungi and principal component analysis (PCA) of SSCP profiles showed that fungal community structure varied significantly between the two ages of vines. Many trunk pathogens, particularly the causal agents of Esca (42-year-old vines) and Eutypa dieback (58-year-old vines), were isolated. However, numerous mycoparasites (e.g., Trichoderma spp.) were also isolated. This decline in foliar symptoms among older vines may reflect an ‘equilibrium’ among trunk pathogens, mycoparasites, and saprobes.