Key words
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Grapevine; fungal diseases; esca; eutypiosis; black dead arm disease; Petri disease; young vine decline; fungal community; endophytes; molecular markers; "direct"-PCR; wood morphology.
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Research programs
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COST-Action 858 - Biotic and abiotic stress Grapevine Defence Mechanism and Grape Development
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Short description
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Fungal trunk diseases of grapevine are worldwide responsible for important economical losses. This project is an extension of a first COST action (April 2005-07) dealing with the interaction of the fungi involved in diseased trunks, production of toxins, the resistance mechanism and the biological control of the disease. This extension of the project will focus on the detection of the different fungal pathogens on the wooded canes used for grafting in nurseries and on the planting material sold to the growers, using molecular markers. This should allow a certification protocol for the grapevine nurseries to guarantee fungal-free planting material.
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Partners and International Organizations
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AT, CH, CY, CZ, DE, ES, FR, GR, HU, IL, IT, LU, PL, PT, RS, SE, SI
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Abstract
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Fungal trunk diseases of grapevine are worldwide responsible for important economical losses. This project focus on an extensive survey and identification of the fungi present in planting material and in wood canes used for grafting in nurseries in relation with the fungal community of old, esca-diseased plants on the field. For planting material, the potential of hot water treatment to control fungi is investigated as well as the expression of fungal secondary metabolites for the species found to be the most frequently associated with symptomatic grape wood. Several fungi involved in esca-diseased trunks are also present in asymptomatic and apparently healthy nursery plants grafted with material issued from the same vineyard. The shift from an endophytic or/and saprotrophic to a pathogenic behaviour suggests that the fungal community associated with grapevine is unbalanced through time. Environmental factors, modifying the physiological status of the plant may be responsible of the pathogenic development of normally asymptomatic species. A molecular phylogeny based on four loci allows to classify fungal species of previously incertae sedis and to determine the fungal community structure of symptomatic and asymptomatic plants. The fungal community present in esca symptomatic and non symptomatic grape wood is dominated by the Sordariomycetes (mainly Hypocreales). A similar fungal community is found in different cultivars of young Vitis vinifera plants cultivated in Switzerland (Humagne blanche, Chasselas, Arvine, Gamaret, and Gamay). From the 713 fungal isolates obtained in pure culture, 66 operational taxonomic units (OTUs) are defined. The results show that the high majority of the fungi isolated are ascomycetes, with a high proportion of Sordariomycetes (mainly Hypocreales, Sordariales and Diaporthales). However different fungal OTUs are associated to the different cultivars. Grafting material and rootstock contribute equally to the fungal community composition. Esca or Petri related species occur sporadically in the different cultivars, with some of them occupying specific tissues or parts of the plant (i.e. Botryosphaeria spp., Phaeomoniella chlamydospora and Phomopsis viticola). Almost 25% of the OTUs are shared by the different plant parts in most of the cultivars, while very few OTUs appear to result from independent inoculations. This suggests a facilitated colonization from the infected material (graft or rootstock) that might be explained by the transportation of fungal particles in the vessels of the xylem. Hot water treatment reduces the total number of fungal species, reduce the number of pathogenic species but allows the development of slow growing species that might be overgrown by pathogenic species (in wood and/or in culture) or absent in non hot water treated plants. Finally, chemical analyses of the confrontation zones of pair-wise growing fungal species reveals new secondary metabolites toxic to plants, bacteria and/or fungi. These metabolites are not expressed in single species cultures. A chemical war between fungal species in physical contact in the wood may explain the high degradation of the wood in esca apoplectic grapes. As the fungal communities found in association with the different cultivars are not involving the same species, it is not surprising to observe a predominance of different esca pathogenic fungal species depending on the geographical areas.
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References in databases
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C06.0105
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