Project title
Incidence of mycoviruses in epidemic and post-epidemic populations of the ash dieback pathogen Chalara fraxinea and evaluation of their potential for biological control of the disease
(acronym CONTROLDIEBACK)
Project partners: Nature Research Centre (the Leading Party, Vilnius, Lithuania) and Swiss Federal Institute for Forest, Snow and Landscape Research WSL (Swiss Partner, Birmensdorf, Switzerland)
Leader of the Lithuanian team: dr. Vaidotas Lygis, senior researcher at the Laboratory of Phytopathogenic Microorganisms (currently, Laboratory of Plant Pathology) of Nature Research Centre.
Leader of the Swiss team: dr. Daniel Rigling, head of the research group Phytopathology
Project duration: 2012.11.01 – 2016.04.30
Project No. LSP-12 041
Project budget: 627,106 EUR (758,414 CHF)
BACKGROUND
The causal agent of mass ash dieback in Europe, relatively recently identified invasive pathogenic fungus ascomycete Chalara fraxinea (teleomorph – Hymenoscyphus fraxineus) was most likely introduced to Europe from eastern Asia. The disease was first recorded in mid 1990’s in eastern Poland and Lithuania and has since then spread across the continent. The dieback has already been recorded in most European countries, including Russia. So far, no effective control measures have been developed against the devastating disease, and proper management strategies for the diseased trees and stands remain unclear. Common ash (Fraxinus excelsior), a tree species the most susceptible to H. fraxineus, is already getting endangered in many regions of Europe.
ABOUT THE PROJECT
In Europe, the dieback of common ash lasts already for two decades (in Lithuania – for more than 15 years), however no effective means to control this devastating disease have been offered so far, and the perspectives for growing ash are obscure. Today, ash stands in Lithuania and neighbouring countries experience a post-epidemic chronic dieback with only a small fraction of asymptomatic trees. In Switzerland, the disease was first reported in 2008 in the north-western part of the country, from where it expanded rapidly to other regions. In many regions of Switzerland an epidemic disease phase is currently observed (spread of the disease is progressing slower in alpine regions due to natural physical barriers). Options for management of this novel forest disease are currently very limited and mainly directed to search for resistance in the host tree. Mycoviruses are commonly found in all major groups of plant pathogenic fungi. Some of these viruses were found to cause debilitating disease or reduce virulence in its fungal host, and thereby have the potential to be used as biological control agents.
Aiming to create and test novel control means of the ash dieback, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) together with partners from the Nature Research Centre (Vilnius, Lithuania) have implemented a collaborative research project „CONTROLDIEBACK“.
The main aim of the project – to characterize epidemic (Swiss) and post-epidemic (Lithuanian) populations of the ash dieback pathogen H. fraxineus in respect to virulence, genetic diversity and occurrence of mycoviruses, and to assess biological control potential of the identified mycoviruses against the disease.
Project objectives
1) to investigate genetic diversity and virulence of H. fraxineus isolates originating from Lithuanian (post-epidemic) and Swiss (epidemic) populations;
2) to screen H. fraxineus for mycoviruses using a metagenomic approach based on next generation sequencing;
3) to characterize the detected mycoviruses and to determine virus incidence in epidemic and post-epidemic populations of the pathogen;
4) to investigate impact of the identified mycoviruses on their host H. fraxineus thus evaluating their biocontrol potential.
MAIN FINDINGS OF THE IMPLEMENTED PROJECT
- old-established (Lithuanian) and recently established (Swiss) populations of H. fraxineus are characterized by high genotypic diversity; neither of the populations showed clear genetic structure;
- genetic differences among the investigated H. fraxineus isolates are non-significant irrespective of their origin; the overall genetic (allelic) diversity in the investigated populations of the fungus is also small. No genetic differentiation and no difference in genetic diversity were detected between the old established and the recently established H. fraxineus populations rejecting the hypothesis of a lower genetic diversity at the epidemic disease front;
- there is no genetic differentiation between isolates recovered from bark lesions (pathogenic phase) and fallen leaf petioles (saprophytic phase) indicating that all H. fraxineus genotypes are potentially able to induce bark infections on living trees and to survive saprophytically, which excludes a niche partitioning;
- as could be judged from mostly bi-allelic nature of loci found in the investigated H. fraxineus isolates, the pathogen was most likely introduced to Europe by only a few (most likely two) individuals, what has determined little genetic diversity in the invasive populations of the fungus (so-called bottleneck effect);
- virulence between H. fraxineus isolates representing recently established (Swiss) populations and old-established (Lithuanian) populations does not differ significantly. This over again confirms the assumption that despite large geographical distance and different time of establishment, Swiss and Lithuanian (and, most likely, all European) populations of H. fraxineus are similar in many aspects (little genetic differentiation; rather short history of ash dieback in Europe for significant mutations to occur; strong gene flow);
- although most of the investigated H. fraxineus isolates were able to induce bark necroses on ash seedlings, a large variation in virulence was observed among different fungal isolates originating even from compact territories;
- a novel mycovirus of the mitovirus family Narnaviridae,- Hymenoscyphus fraxineus mitovirus 1 (HfMV1) has been detected in more than 90% of the investigated H. fraxineus isolates; no significant difference in prevalence of this mycovirus was found between Lithuanian and Swiss populations of the carrier fungus;
- detected in European isolates of H. fraxineus, similarly to its fungal host, mycovirus HfMV1 shows high genotypic but low genetic (nucleotide) diversity, and its European populations also lack genetic structure;
- two genetically divergent HfMV1 haplotype groups are prevalent both in Lithuanian and Swiss H. fraxineus populations (as well as in different subpopulations within those populations); both groups were detected also in Japanese isolates of the fungal host. These results provide additional evidence that only two H. fraxineus isolates, each carrying different mitovirus haplotype, have been introduced from East Asia to Europe;
- high incidence of HfMV1 in the investigated H. fraxineus isolates and populations of the ash dieback pathogen indicates that this mycovirus is well adapted to a vertical transmission into ascospores of H. fraxineus;
- different genotypes of the fungus exhibit clear vegetative incompatibility which prevents anastomosis of the fungal hyphae and, thus, makes horizontal mycovirus transmission between co-existing fungal individuals virtually impossible;
- because mycovirus HfMV1 has no clear phenotypic effects on its fungal host, and because horizontal mycovirus transmission is hardly possible, the potential of mycoviruses carried by H. fraxineus for biological control of the ash dieback disease is doubtful.
Publicity of the achieved results:
Scientific publications:
Schoebel C. N., Zoller S., Rigling D., 2014: Detection and genetic characterisation of a novel mycovirus in Hymenoscyphus fraxineus, the causal agent of ash dieback. Infection, Genetics and Evolution, 28: 78–86. https://doi.org/10.1016/j.meegid.2014.09.001
Burokiene D., Prospero S., Jung E., Marciulyniene D., Moosbrugger K., Norkute G., Rigling D., Lygis V., Schoebel C. N., 2015: Genetic population structure of the invasive ash dieback pathogen Hymenoscyphus fraxineus in its expanding range. Biological Invasions, 17(9): 2743–2756. https://doi.org/10.1007/s10530-015-0911-6
Lygis V., Prospero S., Burokiene D., Schoebel C. N., Marciulyniene D., Norkute G., Rigling D. 2017: Virulence of the invasive ash pathogen Hymenoscyphus fraxineus in old and recently established populations. Plant Pathology, 66(5): 783–791. https://doi.org/10.1111/ppa.12635
Schoebel C., Botella L., Lygis V., Rigling D. 2017: Population genetic analysis of a parasitic mycovirus to infer the invasion history of its fungal host. Molecular Ecology, 26(9): 2482–2497. https://doi.org/10.1111/mec.14048
Schoebel C. N., Prospero S., Gross A., Rigling D. 2018: Detection of a conspecific mycovirus in two closely related native and introduced fungal hosts and evidence for interspecific virus transmission. – Viruses 10(11): 628. https://doi.org/10.3390/v10110628
Pliūra A., Bakys R., Suchockas V., Marčiulynienė D., Gustienė A., Verbyla V., Lygis V. 2017: Ash dieback in Lithuania: disease history, research on impact and genetic variation in disease resistance, tree breeding and options for forest management. In: Vasaitis, R., Enderle, R. (eds.), Dieback of European Ash (Fraxinus spp.): Consequences and Guidelines for Sustainable Management, Swedish University of Agricultural Sciences, Service/Repro, Uppsala, Sweden, pp.150–165. ISBN (print version) 978-91-576-8696-1; ISBN (electronic version) 978-91-576-8697-8 (https://www.slu.se/globalassets/ew/org/inst/mykopat/forskning/stenlid/dieback-of-european-ash.pdf). See article pdf
Queloz V., Hopf S., Schoebel C. N., Rigling D., Gross A. 2017: Ash dieback in Switzerland: history and scientific achievements. In: Vasaitis, R., Enderle, R. (eds.), Dieback of European Ash (Fraxinus spp.): Consequences and Guidelines for Sustainable Management, Swedish University of Agricultural Sciences, Service/Repro, Uppsala, Sweden, pp.150–165. ISBN (print version) 978-91-576-8696-1; ISBN (electronic version) 978-91-576-8697-8 (https://www.slu.se/globalassets/ew/org/inst/mykopat/forskning/stenlid/dieback-of-european-ash.pdf).
Results presented in the international conferences, meetings:
In September 8–12, 2014, members of the Lithuanian team V. Lygis and D. Burokienė took part in the international conference „11th Conference of the European Foundation for Plant Pathology“ (Krakow, Poland), where they have presented research results:
Burokienė D., Jung E., Lygis V., Moosbrugger K., Prospero S., Rigling D., Schoebel C. N., 2014: Genetic differentiation within and between Swiss and Lithuanian populations of Hymenoscyphus pseudoalbidus using microsatellite analysis. – In: Book of Abstracts of the 11th Conference of the European Foundation for Plant Pathology „Healthy Plants – Healthy People“, September 8–13, 2014, Krakow, Poland: p. 71.
Lygis V., Rigling D., Marčiulynienė D., Burokienė D., Schoebel C. N., Norkutė G., 2014: Virulence of Hymenoscyphus pseudoalbidus isolates originating from Lithuanian (post-epidemic) and Swiss (epidemic) populations. – In: Book of Abstracts of the 11th Conference of the European Foundation for Plant Pathology „Healthy Plants – Healthy People“, September 8–13, 2014, Krakow, Poland: p. 72.
Summaries of the oral presentations could be found here:
http://www.kongres-fitopatologiczny.pl/pliki/11_EFPP_Conference_Book-of-abstracts_List-of-Participants.pdf.
In August 2–5, 2014, a member of the Swiss team dr. C. Schoebel took part in the international conference „The Third International Mycovirus Symposium“ (Burlington, VT, USA), where she gave a presentation „Detection and genetic characterisation of a novel mycovirus in Hymenoscyphus fraxineus, the causal agent of ash dieback in Europe“.
In March 23–27, 2014, D. Burokienė and C. Schoebel took part in the international conference „12th European Conference on Fungal Genetics“ (Seville, Spain, http://www.ecfg12.com/cgi.hrb?idexp=EAXQS), where they have presented the research results:
Burokienė D., Jung E., Lygis V., Moosbrugger K., Prospero S., Rigling D., Schoebel C. N., 2014: Genetic population structure of epidemic and post-epidemic populations of the ash dieback pathogen Chalara fraxinea. – In: Book of Abstracts of the 12th European Conference on Fungal Genetics, March 23-27, 2014, Seville, Spain: p. 283.
Schoebel C. N., Jung E., Burokienė D., Prospero S., Lygis V., Rigling D., 2014: Searching for mycoviruses in Chalara fraxinea, the causal agent of ash dieback. – In: Book of Abstracts of the 12th European Conference on Fungal Genetics, March 23-27, 2014, Seville, Spain: p. 266.
Summaries of the poster presentations could be found here:
http://www.ecfg12.com/docs/ABSTRACTSBOOK-ECFG12.pdf.
Member of the Swiss team dr. C. Schoebel has also presented her poster (Schoebel C.N., Zoller S., Jung E., Burokienė D., Moosbruger K., prospero S., Lygis V., Rigling D., 2014: Detection of a novel mycovirus in Chalara fraxinea, the causal agent of ash dieback, using NGS) in the following conferences:
1) Zurich Mycology Symposium (ETH Zurich, Switzerland; January 24, 2014);
2) international EMBO conference “Viruses of Microbes” (Zurich, Switzerland; July 14-18, 2014);
3) „Annual Meeting of the Swiss Society of Phytiatry“(Zurich, Switzerland; September 26, 2014).
Presentations of the results obtained during the implementation of the ‘CONTROLDIEBACK’ project were also given during Management Committee/Working Group meetings/conferences of the COST programme action No. FP1103 FRAXBACK („Fraxinus dieback in Europe: elaborating guidelines and strategies for sustainable management“, http://www.cost.eu/COST_Actions/fps/Actions/FP1103; also see www.fraxback.eu):
Burokienė D., Rigling D., Lygis V., Prospero S., Schoebel C. N., 2014: Genetic structure of epidemic and post-epidemic populations of Hymenoscyphus pseudoalbidus using microsatellite analysis. – COST Action FP1103 FRAXBACK MC & WG Meeting, April 10, 2014, Prague, Czech Republic (oral presentation).
Schoebel C.N., 2014: Detection of a novel mitovirus in Chalara fraxinea, using NGS. – COST Action FP1103 FRAXBACK MC & WG Meeting, April 10, 2014, Prague, Czech Republic (oral presentation).
Burokienė D., Lygis V., 2013: Genetic characterization of Chalara fraxinea populations in Lithuania: preliminary results. – COST Action FP1103 FRAXBACK 4th MC Meeting & Workshop “Frontiers in Ash Dieback Research”, September, 4-6, 2013, Malmö, Sweden (poster presentation).
In June 7-12, 2015, members of the Lithuanian team V. Lygis and D. Burokienė took part in the Joint IUFRO Working Party Meetings: 7.02.02 “Foliage, shoot and stem diseases of forest trees” and 7.03.04 “Diseases and insects in forest nurseries” (Swedish University of Agricultural Sciences SLU, Uppsala, Sweden), where they have presented research results:
Lygis, V., Rigling, D., Burokienė, D., Marčiulynienė, D., Schoebel,C.N., Norkutė, G. 2015. Virulence of Hymenoscyphus fraxineus isolates from Lithuanian (post-epidemic) and Swiss (epidemic) populations. Joint IUFRO Working Party Meetings: 7.02.02 “Foliage, shoot and stem diseases of forest trees” and 7.03.04 “Diseases and insects in forest nurseries”. Swedish University of Agricultural Sciences SLU, Uppsala, Sweden, June 7-12, 2015: abstracts: 88. https://www.iufro.org/download/file/28319/75/70202-70304-uppsala15-abstracts_pdf/
Other project publicity activities
Articles in Lithuanian popular foresters’ journal:
Gustienė A., Lygis V., 2013: Šiandieniniai uosių džiūties tyrimai Europoje. – Mūsų Girios, 11: 8–10.
Gustienė A., Lygis V., 2013: Uosių džiūties problematika šiandien: ką naujo sužinojome? – Mūsų girios, 1: 16–18.
Bakys R., Lygis V. 2016: Kodėl džiūsta Lietuvoje ir Europoje uosiai? – Mūsų Girios, 1: 14–16.
Burokienė, D., Lygis, V. 2019: Kovai su uosynų džiūtimi konsoliduojamos Baltijos šalių ir Vokietijos mokslininkų pajėgos. – Mūsų Girios. 10: 11–12.
Article in Swiss newspaper:
Brügger L., 2013. Forscher vom WSL und aus Litauen kämpfen gegen das Eschensterben. – Limmattaler ZEITUNG (2013.11.06): in a form of an interview (interviewed were D. Rigling and V. Lygis). http://www.urdorf.ch/documents/IntegrationsbeauftragterGemeinde.pdf
An informative article (in a form of an interview) published in a Swiss newspaper „az Limmattaler Zeitung“
Other activities:
The Leading Party has prepared and printed leaflets for publicity of Project activities and promotion of the Lithuanian-Swiss cooperation programme:
http://www.wsl.ch/fe/biodiversitaet/projekte/eschentriebsterben/InfoChalera_LIT. A poster (2 items) advertising the Lithuanian-Swiss cooperation programme and the implemented international collaborative Project has been exhibited in premises of Nature Research Centre. An engaged informative article in Lithuanian national press (in a form of an advertisement) including general information about the Lithuanian-Swiss cooperation programme and the Project, specifying it‘s main aims, objectives and expected results has been published in a newspaper “Valstiečių laikraštis”:
An advertizing poster and An engaged informative article in a newspaper „Valstiečių laikraštis“.
The Swiss Partner has prepared and printed leaflets for publicity of Project activities and promotion of the Lithuanian-Swiss cooperation programme in three languages:
German (http://www.wsl.ch/fe/biodiversitaet/projekte/eschentriebsterben/InfoChalera_DE),
French (http://www.wsl.ch/fe/biodiversitaet/projekte/eschentriebsterben/InfoChalera_FR) and
Italian (http://www.wsl.ch/fe/biodiversitaet/projekte/eschentriebsterben/InfoChalera_IT). An informative article in Swiss national press (in a form of an interview: www.urdorf.ch/documents/IntegrationsbeauftragterGemeinde.pdf) has been published in a newspaper „az Limmattaler Zeitung“. The webpage for publicity of Project activities has been published in an internet site of Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) in
Defended PhD theses:
In 2015, a member of the Leading Party team PhD student Diana Marčiulynienė has successfully defended doctoral dissertation „Characterization of Hymenoscyphus fraxineus populations of different origin and susceptibility of common ash to the dieback pathogen”.
In 2018, a member of the Leading Party team PhD student Goda Norkutė has successfully defended doctoral dissertation „Characterization of populations of invasive pathogens – causal agents of three major forest tree diseases: alder decline, Dutch elm disease and ash dieback“.
Some of the results obtained during implementation of the project activities were included into both theses.
The study was financially supported by Lithuanian-Swiss cooperation programme to reduce economic and social disparities within the enlarged European Union, project grant agreement No. CH-3-ŠMM-01/12.
