This is the report from a BSPP MSc/MRes Bursary.
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Grapevine Trunk Diseases (GTDs) are considered one of the main reasons of grapevine decline, described as reduced productivity and vine longevity, causing important economic losses in viticulture. In the last decade, special emphasis has been put on these biotic disorders, and their increased importance in a changing climate scenario concerns the scientific community.
The GTD Esca complex is extended to several viticultural regions worldwide and sees a greater importance in Europe and the Mediterranean region. In addition, winegrowers face a difficult management and control of this biotic disorder. It is associated to wood inhabiting fungi which cause wood symptoms in grapevine perennial tissues. Besides internal symptoms, vines often express foliar symptoms, which negatively affect the quantity and quality of the production. Since many attempts failed to reproduce and to fulfil the Koch’s postulates for the reproduction of the typical foliar symptoms, the interaction pathogens-symptom is still unclear. Among the three main fungal pathogens associated, the white-rot basidiomycete Fomitiporia mediterranea has recently gained special attention, after treatments acting directly on the presence of white rot or on the abundance of F. mediterranea succeeded in controlling foliar symptoms. Knowledge on this pathogen and other Fomitiporia species associated in the complex, regarding its wood degradation capacity and its participation in the Esca complex, is still fragmented. In addition, the complexity of the disorder requires a deeper analysis of the elements of the disease triangle and some extra aspects such as the endophytic trunk microbiota, anthropogenic practices and time.
This master thesis project included an in vitro morphological and pathogenicity characterisation of different Fomitiporia species and basidiomycetes associated isolated from grapevine in different viticultural regions, and of different F. mediterranea strains isolated from alternative hosts in Europe. Differences between Fomitiporia species could provide clues about their role in symptom development, and about the variations observed in the different wine regions. Similarly, differences in F. mediterranea strains isolated from alternatives hosts could clarify adaptation and host specificity aspects, and contribute to a better understanding of the dispersal process of F. mediterranea. Furthermore, an assessment of in vitro response of different Fomitiporia species against two antagonistic fungi (Trichoderma gamsii and T. asperellum) contributes to gaining knowledge about the diversity of the Fomitiporia genus, and the potential use of some preventive strategies.
The results revealed differences in temperature requirement for some of the species studied, which might be linked to the adaptation to local environmental conditions. Optimal temperatures were also reported for some Fomitiporia species. With higher temperatures expected, special focus should be put on the species better adapted to higher temperatures. Grapevine wood degradation assays showed no differences between Fomitiporia species nor between F. mediterranea strains from alternative hosts. Host specificity was not detected for the F. mediterranea strains studied in these in vitro conditions. Wood degradation rates were different among some grapevine cultivar included, although not in accordance with their reported susceptibility to Esca foliar symptoms. Both Trichoderma species showed antagonistic activity against all Fomitiporia species included in the experiment. Interestingly, we observed some inconsistencies in the modes of action used by these Trichoderma species. It should be added that in vitro assays often fail to picture complex interactions in plants, and that results should be carefully considered.
Elucidating the aetiology of Esca complex will provide a clearer direction for future research. Until then, studies should focus, for instance, on molecular and metabolomic studies on different Fomitiporia species, and the factors and mechanisms underlying the disease triangle. Performing long-term in vivo experiments is essential and would complement the findings hereby presented. Limited management alternatives render preventive measures, such as pruning wound protection by Trichoderma spp., effective strategies. Unknown answers to questions raised from this complex disorder should be addressed through coordinated and integrated research.
This project served as my master thesis at the University of Copenhagen. My interest in plant pathology goes back to my agricultural engineering degree, when I was first introduced to this fascinating field and offered participation in research projects and teaching assistance. During the MSc in Agriculture at the University of Copenhagen, I developed a special interest in woody crops and particularly in grapevine. The university of Florence offered me the opportunity to work on the GTD Esca complex, and consequently broaden my knowledge in plant pathology of woody plants. Since fundamental questions regarding Esca complex are still to be answered, this challenging topic gave me an idea of the complexity of biotic disorders and unquestionably contributed to my formation as a future plant pathologist. Finally, I would like to thank my supervisors David B. Collinge and Laura Mugnai for their support and guidance during this project as well as the BSPP for providing the support that made this project possible.
Nicolás Cauda
University of Copenhagen
Figure legend: A: mature grapevine showing typical Esca foliar symptoms. B: grapevine leaf with chlorotic areas and necrotic stripes, typical of Esca foliar symptoms. C: grapevine cordon exhibiting with rot.
