Dr. Corine Buser-Schöbel

Phytophthora species are a cause for concern due to their invasive potential and the damage they can cause in agriculture, forestry, and natural ecosystems worldwide. Since water plays a crucial role in their dispersal, stream and river baiting is commonly used to survey risk areas for the presence of quarantine Phytophthora species. However, our understanding of the distribution and diversity of Phytophthora species in European watercourses remains incomplete. This study investigated the presence and diversity of Phytophthora species in Swiss watercourses, with a focus on the highly urbanized Swiss Plateau. Over the period 2012–2016, we sampled 32 watercourses, including major rivers and smaller streams. We isolated Phytophthora on selective media and sequenced the internal transcribed spacer region to identify the species. We recovered 241 Phytophthora isolates, representing 11 species from five major clades. Phytophthora clade 6 prevailed, with P. lacustris being the most common, found in 94.7% of the watercourses. The number of Phytophthora species per watercourse ranged from one to five, with no correlation to watercourse complexity. Our study reveals the presence of six previously unreported species in Switzerland, while known invasive species were not found. Watercourses appear less suited to detect invasive pathogenic Phytophthora species with a still limited distribution in the environment.

Durch den fortschreitenden Lebensraumverlust verringert sich die genetische Vielfalt und somit die Anpassungsfähigkeit der Arten. Im Rahmen der Biodiversitätskonvention hat sich die Schweiz verpflichtet, diesen Verlust der genetischen Vielfalt zu bewerten, zu überwachen und letztendlich zu stoppen. Es gibt jedoch (noch) keine systematische Erfassung innerartlicher genetischer Daten, die diesen Prozess unterstützen könnte und auf die Bedürfnisse der Naturschutzpraxis zugeschnitten ist. Mit einer schweizweiten Datenbank zur innerartlichen genetischen Vielfalt soll sich dies nun ändern.

La perte progressive d’habitats a un impact négatif sur la diversité génétique, qui est la clé de la capacité d’adaptation des espèces. En signant la Convention sur la diversité biologique, la Suisse s’est engagée à évaluer, surveiller et, à terme, enrayer cette érosion de la diversité des gènes. Or, il n’existe à ce jour aucun recueil systématique de données adapté aux besoins de la pratique de la conservation qui puisse faciliter ce processus. Un projet de banque de données nationale sur la diversité génétique intraspécifique se propose de combler ce vide.

Background: global trade in living plants and plant material has significantly increased the geographic distribution of many plant pathogens. As a consequence, several pathogens have been first found and described in their introduced range where they may cause severe damage on naïve host species. Knowing the center of origin and the pathways of spread of a pathogen is of importance for several reasons, including identifying natural enemies and reducing further spread. Several Phytophthora species are well-known invasive pathogens of natural ecosystems, including Phytophthora multivora. Following the description of P. multivora from dying native vegetation in Australia in 2009, the species was subsequently found to be common in South Africa where it does not cause any remarkable disease. There are now reports of P. multivora from many other countries worldwide, but not as a commonly encountered species in natural environments.
Results: a global collection of 335 isolates from North America, Europe, Africa, Australia, the Canary Islands, and New Zealand was used to unravel the worldwide invasion history of P. multivora, using 10 microsatellite markers for all isolates and sequence data from five loci from 94 representative isolates. Our population genetic analysis revealed an extremely low heterozygosity, significant non-random association of loci and substantial genotypic diversity suggesting the spread of P. multivora readily by both asexual and sexual propagules. The P. multivora populations in South Africa, Australia, and New Zealand show the most complex genetic structure, are well established and evolutionary older than those in Europe, North America and the Canary Islands.
Conclusions: according to the conducted analyses, the world invasion of P. multivora most likely commenced from South Africa, which can be considered the center of origin of the species. The pathogen was then introduced to Australia, which acted as bridgehead population for Europe and North America. Our study highlights a complex global invasion pattern of P. multivora, including both direct introductions from the native population and secondary spread/introductions from bridgehead populations.

Die jährlichen Erhebungen zum Vorkommen von waldrelevanten Quarantäneschädlingen in der Schweiz wurden in Jungpflanzenbetrieben, in privaten und öffentlichen Grünflächen und im Wald durchgeführt. Zusätzlich wurden Warenimporte mit Verpackungsholz kontrolliert. Nicht gefunden wurden der Zitrusbockkäfer (Anoplophora chinensis / CLB), der Pechkrebs der Föhre (Gibberella circinata), der Kiefernholznematode (Bursaphelenchus xylophilus) und der gefährliche Pappelblattrost (Melampsora medusae). Die Schweiz gilt damit weiterhin als frei von diesen Schadorganismen.
Auch bezüglich des Asiatischen Laubholzbockkäfers (Anoplophora glabripennis / ALB) gab es 2018 keine neuen Befälle im Gebiet der bisherigen Befallsherde. Neben dem Erstbefall der Schweiz in Brünisried, der seit Februar 2018 offiziell als getilgt gilt, wird auch der Befall von Marly ab Ende 2018 als getilgt gelten. Die Untersuchungen der Verpackungsholzkontrollproben 2018 ergaben keinen positiven ALB-Befund, es handelte sich um andere eingeschleppte Käfer- und Insektenarten. [...]

Les suivis annuels sur la présence d'organismes de quarantaine importants pour la forêt en Suisse ont été réalisées dans des pépinières, dans des espaces verts privés et publics et dans la forêt. En outre, les importations de marchandises contenant du bois d'emballage ont été contrôlées.
Le capricorne asiatique des agrumes (Anoplophora chinensis/CAA), le chancre résineux du pin (Gibberella circinata), le nématode du pin (Bursaphelenchus xylophilus) et la dangereuse rouille foliaire des peupliers (Melampsora medusae) n’ont pas été détectés. La Suisse est donc toujours considérée comme indemne de ces organismes nuisibles.
En ce qui concerne le capricorne asiatique (CA), aucun nouveau cas n’a été découvert dans les foyers connus en Suisse. Le premier foyer, à Brünisried, a été officiellement éradiqué en février 2018, et celui de Marly le sera également d'ici fin 2018. Lors des recherches sur les échantillons de bois d'emballage de 2018, seules d'autres espèces d'insectes introduits ont été découvertes. [...]

Decline diseases are typically caused by complex abiotic and biotic interactions and characterized by a suite of symptoms indicative of low plant vigour. Diseased trees are frequently infected by Phytophthora, but the complex interactions between pathogen, host and the heterogeneous forest environment mask a comprehensive understanding of the aetiology. In the present study, we surveyed European beech (Fagus sylvatica) stands in Swiss forests with recent increases in bleeding lesions for the presence of Phytophthora. We used a combined approach of analysing soil and bark samples from trees displaying bleeding lesions and trees free from bleeding lesions. Soil baiting revealed a higher prevalence of Phytophthora spp. around trees with bleeding lesions than around trees without bleeding lesions. For the bark samples from bleeding lesions, we used several detection methods. Phytophthora spp. were detected in 74% of the trees by an immunological on‐site diagnostic kit, in 64% by a specific PCR assay, and 38% by isolation on selective media. All samples tested were negative for P. ramorum using qPCR. Overall, nine Phytophthora species were identified by ITS sequencing, the most common of which were P. plurivora, P. gonapodyides, P. × cambivora and P. syringae. We identified distinct species in bleeding lesions and the rhizosphere of the same host tree which suggests a multispecies Phytophthora disease patterns in these declining beech. Among the recovered species, P. × cambivora and P. × serendipita were identified as hybrid genotypes with the former abundant in bleeding lesions.

Das Nationale Monitoring von zwei besonders gefährlichen Föhrenkrankheiten 2016 (Föhrenmonitoring 2016) hat gezeigt, dass die Rotbandkrankheit (RBK) und die Braunfleckenkrankheit (BFK) in der Nordschweiz relativ weit aber nicht flächendecken verbreitet sind und nicht alle Gebiete erreicht haben. Für die RBK wurden Dothistroma septosporum und D. pini, für die BFK Lecanosticta acicola als Erreger nachgewiesen. Da dieses Monitoring auf punktuellen Stichproben beruhte und wenig über die Ausdehnung und die Befallsintensität der Bäume in den einzelnen Wäldern aussagte, sollte in der hier vorgestellten Studie dieses für ausgewählte Standorte untersucht werden. Zusätzlich sollte das Vorkommen von RBK auf Fichte näher untersucht werden.

Phytophthora ramorum befällt zahlreiche Gehölzpflanzen in Europa und Nordamerika. Im Westen der USA verursacht der Erreger ein verbreitetes Eichensterben. In Europa sind bis jetzt hauptsächlich Ziersträucher betroffen. Seit einigen Jahren treten in Grossbritannien und Frankreich auch grössere Schäden an Japanlärchen auf

Bei Phytophthora denken wir in erster Linie an die Kartoffelfäule und die grosse Hungersnot in Irland. Jedoch gibt es auch zahlreiche Phytophthora-Arten, die Schäden an Bäumen und Sträuchern verursachen. Welche das sind, wie Sie die Symptome erkennen und was Sie dagegen tun können, lesen Sie in einer vierteiligen Serie.

Il deperimento del frassino (o disseccamento dei germogli del frassino) è una grave malattia degli alberi causata da un fungo (Hymenoscyphus fraxineus) originario dell’Asia orientale. Questo agente patogeno altamente infettivo è stato presumibilmente introdotto in Europa assieme a materiale vegetale all’inizio del decennio del 1990, diffondendosi poi in forma epidemica. In Svizzera, il deperimento del frassino è stato segnalato la prima volta nel 2008 nella regione di Basilea. La malattia si è in seguito propagata a tutte le regioni del Paese. Allo stato attuale delle conoscenze non è ancora nota nessuna misura efficace contro questo patogeno e pertanto l’esistenza del frassino quale specie arborea di pregio è da ritenere minacciata.

Hymenoscyphus albidus is a native fungus in Europe where it behaves as a harmless decomposer of leaves of common ash. Its close relative Hymenoscyphus fraxineus was introduced into Europe from Asia and currently threatens ash (Fraxinus sp.) stands all across the continent causing ash dieback. H. fraxineus isolates from Europe were previously shown to harbor a mycovirus named Hymenoscyphus fraxineus Mitovirus |1 (HfMV1). In the present study, we describe a conspecific mycovirus that we detected in H. albidus. HfMV1 was consistently identified in H. albidus isolates (mean prevalence: 49.3%) which were collected in the sampling areas before the arrival of ash dieback. HfMV1 strains in both fungal hosts contain a single ORF of identical length (717 AA) for which a mean pairwise identity of 94.5% was revealed. The occurrence of a conspecific mitovirus in H. albidus and H. fraxineus is most likely the result of parallel virus evolution in the two fungal hosts. HfMV1 sequences from H. albidus showed a higher nucleotide diversity and a higher number of mutations compared to those from H. fraxineus, probably due to a bottleneck caused by the introduction of H. fraxineus in Europe. Our data also points to multiple interspecific virus transfers from H. albidus to H. fraxineus, which could have contributed to the intraspecific virus diversity found in H. fraxineus.

Phytophthora ist hauptsächlich in Verbindung mit der Kartoffel bekannt. Zu dieser Gattung zählen aber auch Arten, die Schäden an Bäumen und holzigen Pflanzen verursachen. Wie Sie die Symptome erkennen und was Sie tun können, lesen Sie im folgenden Beitrag

Following its introduction from Asia in the 1990s, the ascomycete Hymenoscyphus fraxineus has caused a severe dieback of Fraxinus excelsior in Europe. In this study, the virulence of 200 H. fraxineus isolates were assessed and compared. These isolates equally represented (i) two geographically distant populations with a different disease history (Switzerland, recently established populations at the epidemic front versus Lithuania, old established populations), and (ii) isolates from two different types of host tissue (necrotic bark lesions as dead-end tissue versus fallen leaf petioles as primary host tissue). Inoculations conducted on 3-year-old F. excelsior seedlings showed that the vast majority of the isolates (98%) were able to induce necrotic bark lesions after 10 months. Although a high variation in virulence was observed among isolates, no significant differences were detected between the older and the epidemic-front populations. Decline in virulence of populations of invasive organisms is generally assumed with increasing age of epidemics. However, this does not appear to hold true for H. fraxineus. Either the Lithuanian population is still too young (15 to 20 years old) to show a decline in virulence, or the size of the host population may still not be critical for pathogen survival. Given that bark lesions represent an epidemiological dead end and do not benefit the survival of H. fraxineus, a trend towards reduced 'bark virulence' of isolates originating from leaf petioles compared to isolates from the bark lesions was expected. However, such a trend was observed neither in old, nor in recently established populations.

Monitorings at different spatial scales were done in Switzerland to assess the spread of ash dieback throughout the country. The disease was first observed in 2008 and completely invaded Switzerland seven years later. Most ash trees nowadays suffer to a certain degree from ash dieback. However, the decline process is slow and some trees show tolerance or resistance. Swiss researchers contributed to the current knowledge of ash dieback in different topics: taxonomy and biology of the pathogen, population genetics, host-spectrum as well as biocontrol potential of antagonistic organisms.

Hymenoscyphus fraxineus mitovirus 1 (HfMV1) occurs in the fungus Hymenoscyphus fraxineus, an introduced plant pathogen responsible for the devastating ash dieback epidemic in Europe. Here, we explored the prevalence and genetic structure of HfMV1 to elucidate the invasion history of both the virus and the fungal host. A total of 1298 H. fraxineus isolates (181 from Japan and 1117 from Europe) were screened for the presence of this RNA virus and 301 virus-positive isolates subjected to partial sequence analysis of the viral RNA polymerase gene. Our results indicate a high mean prevalence (78.7%) of HfMV1 across European H. fraxineus isolates, which is supported by the observed high transmission rate (average 83.8%) of the mitovirus into sexual spores of its host. In accordance with an expected founder effect in the introduced population in Europe, only 1.1% of the Japanese isolates were tested virus positive. In Europe, HfMV1 shows low nucleotide diversity but a high number of haplotypes, which seem to be subject to strong purifying selection. Phylogenetic and clustering analysis detected two genetically distinct HfMV1 groups, both present throughout Europe. This pattern supports the hypothesis that only two (mitovirus-carrying) H. fraxineus individuals were introduced into Europe as previously suggested from the bi-allelic nature of the fungus. Moreover, our data points to reciprocal mating events between the two introduced individuals, which presumably initiated the ash dieback epidemic in Europe.