Vertical spread of Hymenoscyphus fraxineus propagules

Currently, the ash dieback causal agent Hymenoscyphus fraxineus is an established invasive pathogen in most European countries. Its potential to spread quickly among invaded forests is based on its propagules: airborne inoculum composed mainly of ascospores originated in apothecia growing on leaf litter infected during the previous vegetation season. The spread of the inoculum by air masses to distant areas is probable and depends on the availability of the ascospores in higher levels of air. Our study aimed to detect the inoculum in an infected area at heights of more than 20 meters. Our study was conducted in a municipal locality (Boršov nad Vltavou) with tens of infected ash trees (Fraxinus excelsior) in South Bohemia (SW Czechia). The infected trees surround an agricultural silo where five rotating arm spore traps (rotorods) were mounted for ten consequent 48h samplings during the peak of the sporulating season (17th July to 6th August 2020). The spore traps were mounted 48, 37, 25, 14 and 0,3 meters above ground. Samples were quantified by qPCR. Results clearly proved the ability of the spores to reach a height of 48 meters. Furthermore, H. fraxineus DNA was detected from all five spore traps during all ten samplings. Mostly, the amount of detected spores showed a decreasing trend with height, and varied a lot. During some of the samplings, higher spore concetrations were achieved at the top than at the lower traps, which can be explained by horizontal air transfer of the inoculum from other infected areas. Based on GLM analyses, higher spore concentrations were achieved during days without rain, lower air temperatures, after cloudy, humid and rainy weather without strong winds. A combination of rotorod ROTTRAP 52 with qPCR quantification proved to be an efficient technology for a study focused on the vertical spread of H. fraxineus propagules.O

Worldwide tests of generic attractants, a promising tool for early detection of non-native cerambycid species

A large proportion of the insects which have invaded new regions and countries are emerging species, being found for the first time outside their native range. Being able to detect such species upon arrival at ports of entry before they establish in non-native countries is an urgent challenge. The deployment of traps baited with broad-spectrum semiochemical lures at ports-of-entry and other high-risk sites could be one such early detection tool. Rapid progress in the identification of semiochemicals for cerambycid beetles during the last 15 years has revealed that aggregation-sex pheromones and sex pheromones are often conserved at global levels for genera, tribes or subfamilies of the Cerambycidae. This possibly allows the development of generic attractants which attract multiple species simultaneously, especially when such pheromones are combined into blends. Here, we present the results of a worldwide field trial programme conducted during 2018-2021, using traps baited with a standardised 8-pheromone blend, usually complemented with plant volatiles. A total of 1308 traps were deployed at 302 sites covering simultaneously or sequentially 13 European countries, 10 Chinese provinces and some regions of the USA, Canada, Australia, Russia (Siberia) and the Caribbean (Martinique). We intended to test the following hypotheses: 1) if a species is regularly trapped in significant numbers by the blend on a continent, it increases the probability that it can be detected when it arrives in other countries/continents and 2) if the blend exerts an effective, generic attraction to multiple species, it is likely that previously unknown and unexpected species can be captured due to the high degree of conservation of pheromone structures within related taxa. A total of 78,321 longhorned beetles were trapped, representing 376 species from eight subfamilies, with 84 species captured in numbers greater than 50 individuals. Captures comprised 60 tribes, with 10 tribes including more than nine species trapped on different continents. Some invasive species were captured in both the native and invaded continents. This demonstrates the potential of multipheromone lures as effective tools for the detection of 'unexpected' cerambycid invaders, accidentally translocated outside their native ranges. Adding new pheromones with analogous well-conserved motifs is discussed, as well as the limitations of using such blends, especially for some cerambycid taxa which may be more attracted by the trap colour or other characteristics rather than to the chemical blend.O

Conditions of emergence of the Sooty Bark Disease and aerobiology of Cryptostroma corticale in Europe

The sooty bark disease (SBD) is an emerging disease affecting sycamore maple trees (Acer pseudoplatanus) in Europe. Cryptostroma corticale, the causal agent, putatively native to eastern North America, can be also pathogenic for humans causing pneumonitis. It was first detected in 1945 in Europe, with markedly increasing reports since 2000. Pathogen development appears to be linked to heat waves and drought episodes. Here, we analyse the conditions of the SBD emergence in Europe based on a three-decadal time-series data set. We also assess the suitability of aerobiological samples using a species-specific quantitative PCR assay to inform the epidemiology of C. corticale, through a regional study in France comparing two-year aerobiological and epidemiological data, and a continental study including 12 air samplers from six countries (Czechia, France, Italy, Portugal, Sweden and Switzerland). We found that an accumulated water deficit in spring and summer lower than -132 mm correlates with SBD outbreaks. Our results suggest that C. corticale is an efficient airborne pathogen which can disperse its conidia as far as 310 km from the site of the closest disease outbreak. Aerobiology of C. corticale followed the SBD distribution in Europe. Pathogen detection was high in countries within the host native area and with longer disease presence, such as France, Switzerland and Czech Republic, and sporadic in Italy, where the pathogen was reported just once. The pathogen was absent in samples from Portugal and Sweden, where the disease has not been reported yet. We conclude that aerobiological surveillance can inform the spatial distribution of the SBD, and contribute to early detection in pathogen-free countries.O

Conditions of emergence of the Sooty Bark Disease and aerobiology of Cryptostroma corticale in Europe

The sooty bark disease (SBD) is an emerging disease affecting sycamore maple trees (Acer pseudoplatanus) in Europe. Cryptostroma corticale, the causal agent, putatively native to eastern North America, can be also pathogenic for humans causing pneumonitis. It was first detected in 1945 in Europe, with markedly increasing reports since 2000. Pathogen development appears to be linked to heat waves and drought episodes. Here, we analyse the conditions of the SBD emergence in Europe based on a three-decadal time- series data set. We also assess the suitability of aerobiological samples using a species-specific quantitative PCR assay to inform the epidemiology of C. corticale, through a regional study in France comparing two- year aerobiological and epidemiological data, and a continental study including 12 air samplers from six countries (Czechia, France, Italy, Portugal, Sweden and Switzerland). We found that an accumulated water deficit in spring and summer lower than -132 mm correlates with SBD outbreaks. Our results suggest that C. corticale is an efficient airborne pathogen which can dis- perse its conidia as far as 310 km from the site of the closest disease outbreak. Aerobiology of C. corticale followed the SBD distribution in Europe. Pathogen detection was high in countries within the host native area and with longer disease presence, such as France, Switzerland and Czech Republic, and sporadic in Italy, where the pathogen was reported just once. The pathogen was absent in samples from Portugal and Sweden, where the disease has not been reported yet. We conclude that aerobiological surveillance can inform the spatial distribution of the SBD, and contribute to early detection in pathogen-free countriesinfo:eu-repo/semantics/publishedVersio

Global Geographic Distribution and Host Range of Fusarium circinatum, the Causal Agent of Pine Pitch Canker

Funding: This study was financially supported by COST Action FP1406 (PINESTRENGTH), the Estonian Science Foundation grant PSG136, the Forestry Commission, United Kingdom, the Phytophthora Research Centre Reg. No. CZ.02.1.01/0.0/0.0/15_003/0000453, a project co-financed by the European Regional Development Fund. ANSES is supported by a grant managed by the French National Research Agency (ANR) as part of the “Investissements d’Avenir” programme (ANR-11-LABX-0002-01, Laboratory of ExcellenceARBRE). SW was partly supported by BBSRC Grant reference BB/L012251/1 “Promoting resilience of UK tree species to novel pests & pathogens: ecological & evolutionary solutions (PROTREE)” jointly funded by BBSRC, Defra, ESRC, the Forestry Commission, NERC and the Scottish Government, under the Tree Health and Plant Biosecurity Initiative. Annual surveys in Switzerland were financially supported by the Swiss Federal Office for the Environment FOEN. Acknowledgments: Andrea Kunova and Cristina Pizzatti are acknowledged for the assistance in the sampling. Thanks are due to Dina Ribeiro and Helena Marques from ICNF-Portuguese Forest Authority for providing location coordinates. We thank three anonymous reviwers for valuable corrections and suggestions.Peer reviewedPublisher PD

Volumetric Spore Traps Are a Viable Alternative Tool for Estimating Heterobasidion Infection Risk

Prophylactic stump treatments against the conifer root rot fungus Heterobasidion annosum s.l. should take into account the airborne inoculum density of the pathogen, in order to be economically feasible. Our objective was to test if an automatic volumetric spore trap (AVST) could be used as a sensitive alternative of passive traps for quantifying Heterobasidion airspora in forest stands. The routinely used wood disc exposure method (WDE) was implemented simultaneously with AVST in five coniferous monocultures and three near-natural stands without silvicultural management in Czechia. Air sampling took place for 24-h intervals in five months of the main sporulation period. The atmospheric concentration of H. annosum s.l. spores (cHa) was determined by qPCR with generic and species-specific primers. AVST detected more target species than WDE on 77% of sampling occasions. When comparing the relative abundance of the three European H. annosum s.l. species detected by AVST and WDE, H. parviporum and H. abietinum were found to be overrepresented on wood discs. cHa in November was significantly higher than in May and June, confirming the seasonal pattern typical for temperate Europe. For an accurate and rapid estimation of Heterobasidion primary infection risk, the usage of AVST is highly recommended

Volumetric Spore Traps Are a Viable Alternative Tool for Estimating <i>Heterobasidion</i> Infection Risk

Prophylactic stump treatments against the conifer root rot fungus Heterobasidion annosum s.l. should take into account the airborne inoculum density of the pathogen, in order to be economically feasible. Our objective was to test if an automatic volumetric spore trap (AVST) could be used as a sensitive alternative of passive traps for quantifying Heterobasidion airspora in forest stands. The routinely used wood disc exposure method (WDE) was implemented simultaneously with AVST in five coniferous monocultures and three near-natural stands without silvicultural management in Czechia. Air sampling took place for 24-h intervals in five months of the main sporulation period. The atmospheric concentration of H. annosum s.l. spores (cHa) was determined by qPCR with generic and species-specific primers. AVST detected more target species than WDE on 77% of sampling occasions. When comparing the relative abundance of the three European H. annosum s.l. species detected by AVST and WDE, H. parviporum and H. abietinum were found to be overrepresented on wood discs. cHa in November was significantly higher than in May and June, confirming the seasonal pattern typical for temperate Europe. For an accurate and rapid estimation of Heterobasidion primary infection risk, the usage of AVST is highly recommended

Spore Dispersal Patterns of Fusarium circinatum on an Infested Monterey Pine Forest in North-Western Spain

The airborne inoculum of Fusarium circinatum Nirenberg &amp; O’Donnell, the fungal pathogen causing Pine Pitch Canker (PPC), is one of the main means of spread of the disease in forest stands and forest nurseries. Since this world-wide known pathogen was introduced in Europe, its biology in this newly infested area still remains scarcely known. To shed more light on this topic, we set up an experiment on a naturally PPC infested forest of Monterey pine in Galicia (NW Spain) with the following two goals: (i) to describe the seasonal spore dispersal pattern during one year of regular sampling and (ii) to assess the spatial spore dispersal pattern around the infested plot. Portable rotating arm spore traps were used and complemented with meteorological measurements. The abundance of F. circinatum spores in the samples was assessed by quantitative PCR (qPCR) with a hydrolysis probe. The results showed almost permanent occurrence of the air inoculum throughout the whole year, being detected in 27 of the 30 samplings. No clear temporal trends were observed, but a higher air inoculum was favoured by previous lower air temperatures and lower leaf wetness. Conversely, neither rainfall nor air humidity seemed to have any significant importance. The spatial spread of the inoculum was noted to be successful up to a distance of 1000 m in the wind direction, even with winds of just 5 m·s−1. Our study shows that rotating arm spore traps combined with qPCR may be an efficient tool for F. circinatum detection