Architecture of an Antagonistic Tree/Fungus Network: The Asymmetric Influence of Past Evolutionary History

Compartmentalization and nestedness are common patterns in ecological networks. The aim of this study was to elucidate some of the processes shaping these patterns in a well resolved network of host/pathogen interactions.Based on a long-term (1972-2005) survey of forest health at the regional scale (all French forests; 15 million ha), we uncovered an almost fully connected network of 51 tree taxa and 157 parasitic fungal species. Our analyses revealed that the compartmentalization of the network maps out the ancient evolutionary history of seed plants, but not the ancient evolutionary history of fungal species. The very early divergence of the major fungal phyla may account for this asymmetric influence of past evolutionary history. Unlike compartmentalization, nestedness did not reflect any consistent phylogenetic signal. Instead, it seemed to reflect the ecological features of the current species, such as the relative abundance of tree species and the life-history strategies of fungal pathogens. We discussed how the evolution of host range in fungal species may account for the observed nested patterns.Overall, our analyses emphasized how the current complexity of ecological networks results from the diversification of the species and their interactions over evolutionary times. They confirmed that the current architecture of ecological networks is not only dependent on recent ecological processes

First report of Dothistroma pini, a recent agent of the Dothistroma needle blight (DNB), on Pinus radiata in France

Dothistroma needle blight (DNB), also known as red band needle blight, is an important fungal disease of Pinus spp. that occurs worldwide. On the basis of molecular and morphological studies of the anamorphic stage, Barnes et al.(1) showed that two closely related species were involved in DNB: Dothistroma septosporum (Dorog.) Morelet and Dothistroma pini Hulbary. D. septosporum (teleomorph: Mycosphaerella pini Rostr.) has a worldwide distribution and is reported as the species that caused past epidemics of DNB. This species is reported on more than 80 different pine species, and P. radiata D. Don (Monterey pine) is classified as a highly or moderately susceptible species, depending on the published sources (4). D. pini (telemorph: unknown) was initially found on needles of P. nigra J. F. Arnold collected from 1964 to 2001 in North Central U.S.A. (Minnesota, Nebraska and Michigan). It was subsequently found in Ukraine and southwestern Russia, where it has been associated with the emergence of DNB on P. nigra subsp. pallasiana (Lamb.) Holmboe, in Hungary on P. nigra and in Russia on P. mugo Turra (1). In France, D. pini was reported for the first time on P. nigra, and was sometimes found in association with D. septosporum on the same needles (3). Later on, a more intensive survey of DNB was launched in France and 216 stands of Pinus sp. were studied. D. septosporum and D. pini were detected in 133 and 123 stands, respectively. Both species co-occurred in 40 stands but D. pini was only found on P. nigra (subsp. laricio and austriaca) (2). Up to now, D. pini was therefore only reported on European pine species, mainly on the different allopatric subspecies belonging to the black pine complex and on one occasion on P. mugo, which belongs to the same section and subsection as P. nigra. In March 2011, typical symptoms of DNB (needles with orangey-red brown distal ends, dark red bands and green bases; small and black fruit bodies within the bands) were observed in a 50 to 60-years old P. radiata stand, of approximately 3 ha., located in the Pyrénées Atlantiques, close to the Spanish border (Sare, 1° 36' 08'' West; 43° 19' 51'' North). The density of pine was relatively low and patches of natural regeneration were present. Although nearly all of the trees showed DNB symptoms, less than 50% of their needles were affected by the disease. In this stand, needles showing typical DNB symptoms were randomly taken from 4 pines and mixed together to form a single sample for analysis. Total DNA was extracted from symptomatic needle pieces. The presence of Dothistroma pini was confirmed by a specific multiplex real-time polymerase chain reaction (PCR) analysis using the D. pini-specific primers/probe combination DPtef-F1-/R1/-P1 (3), and by sequencing a D. pini-specific amplicon generated by another conventional PCR (3) using DPtef-F/DPtef-R primers (GenBank accession KC853059) (3). D. septosporum was not detected in the sample. To our knowledge, this is the first report worldwide of D. pini on P. radiata which is a pine species largely planted in Spain and in the Southern Hemisphere. This is also the first report of this pathogen on a non-European pine species. The original native range and the host range of D. pini remain unknown and there is currently no data about host preferences or aggressiveness on different pine species

Ash dieback or chalarose - what do we know?

Le Frêne commun, Fraxinus excelsior, est menacé par un champignon pathogène récemment identifié, Hymenoscyphus pseudoalbidus (forme asexuée, Chalara fraxinea ). Cette maladie, la chalarose, apparue au Nord-Est de l’Europe dans les années 1990, s’est disséminée dans une grande partie de l’aire naturelle du Frêne commun. Détectée en France en 2008, elle affecte fin 2011 les frênaies du Nord et de l’Est du territoire et s’est rapidement étendue jusque dans le Massif central. Les multiples symptômes de cette nouvelle maladie sont décrits. L’accent est mis sur les nécroses corticales qui apparaissent au collet des arbres. Ce n’est que très récemment que ce symptôme a été attribué à H. pseudoalbidus. La rapidité de l’évolution des symptômes dans les peuplements est abordée grâce aux premiers résultats d’un suivi symptomatologique réalisé sur un réseau de placettes. Cet article est l’occasion de dresser un bilan des connaissances sur la biologie de ce nouveau pathogène, de décrire la situation des pays atteints et d’aborder les recommandations de gestion.Common ash ( Fraxinus excelsior) is threatened by a recently identified fungal pathogen Hymenoscyphus pseudoalbidus (asexual form Chalara fraxinea). This disease is called ash dieback or "Chalarose" in French. It appeared in north-eastern Europe in the mid 1990's, and has since spread across most of the natural range for common ash. The disease was first detected in France in 2008. The Forest Health Department (DSF) has implemented a monitoring scheme for fungus presence throughout France along with its progression over time. By the end of 2009, 13 French Departements were infected in north-eastern France, along with one isolated outbreak in the north of France. One year later in 2010, 18 Departements were infected, and their number grew to 29 in 2011, with fungus infections spanning the north-northeast of France, reaching the Massif Central in the centre of France. Ascospores may be the only mode of fungal spread. They develop during the summer from apothecia that grow on previous year's ash leaf petioles and rachises in the forest litter. A study is underway in France to assess ascospore dispersal. A wide range of symptoms characterizes the disease. These include leaf wilting, foliage necrosis, shoot dieback, orange bark necrosis, premature leaf fall, overall defoliation, and abnormal colour of the wood. These symptoms change with time. Special emphasis is placed on cortical necrosis that appears in the tree collar. A French team of scientists only very recently established the connection between this symptom and H. pseudoalbidus. Very severe forms of these necroses are found in populations that were the first to be affected by the disease in France. A study conducted in the first French Departement to be infected shows that necrotic foci are found everywhere, albeit small in size. From the Forest Health Department's findings, it appears that trees with foliage necrosis in the collar do not necessarily show signs of defoliation in the tree crown. The two mechanisms of infection (foliage/shoot necrosis and collar necrosis) thus seem distinct - a hypothetical new disease cycle for ash dieback is proposed. In 2010, the DSF put up a network of monitoring plots on adult trees in contaminated areas. This will help better measure the way symptoms progress in infected populations as well as give a better estimate of the overall impact of the fungus on ash. Preliminary results are discussed and compared with those from studies under-taken in other countries, showing that mortality is not apparent after two years and appears to progress very slowly. In France, the first adult trees died around three years after infection. The disease is often first detected in seedlings and appears in adults only later. Overall, all ages and landscapes are susceptible to infection. Current recommendations for forestry management in France are comparable to those coming from other infected European countries: no more investment in ash as a species, selective harvest of infected trees while apparently tolerant trees are kept in place where possible so that potential naturally occurring resistance in ash population is not destroyed. Log transport is allowable after removal of necrosis-bearing zones, since the fungus is absent from healthy wood. When infected parts are removed, the risk of infection disappears. The article also explains why different countries react differently to the disease

La graphiose : une histoire ancienne toujours d'actualité

La graphiose est le champignon responsable du dépérissement des ormes. À l’heure actuelle, aucun fongicide à la fois efficace, sélectif et peu toxique n’est disponible pour lutter à grande échelle contre ce fléau. De même, il n’existe pas d’insecticide efficace contre le scolyte, insecte vecteur de la graphiose

La graphiose : une histoire ancienne toujours d'actualité

La graphiose est le champignon responsable du dépérissement des ormes. À l’heure actuelle, aucun fongicide à la fois efficace, sélectif et peu toxique n’est disponible pour lutter à grande échelle contre ce fléau. De même, il n’existe pas d’insecticide efficace contre le scolyte, insecte vecteur de la graphiose

Changes in Forest Health Status over the Last Thirty years

En France, le Département de la santé des forêts a en charge la surveillance sylvosanitaire depuis sa création en 1989. L’analyse des observations spontanées réalisées au cours de la veille sanitaire sur l’ensemble du territoire et de celles effectuées à période fixe au niveau d’un réseau systématique de placettes (partie française du réseau européen de suivi des dommages forestiers) permet de conclure que le paysage entomologique a peu évolué au cours des trente dernières années. Par contre, le paysage sylvosanitaire pathologique a fortement changé du fait de l’introduction ancienne ou récente d’agents pathogènes nouveaux. Il ressort ainsi que la principale menace sur les forêts est, du fait des échanges internationaux, l’arrivée de bioagresseurs exotiques dont l’expression (installation, émergence, épidémie...) peut être favorisée par les changements climatiques en cours.In France, the forest health department has been in charge of forest health surveillance since it was set up in 1989. An analysis of spontaneous observations conducted under the health surveillance scheme all over France and those performed at given periodic intervals in a systematic network of plots (the French part of the European monitoring network of damage to trees) show there has been little change in the situation of entomological populations. In contrast, the status of diseased forests has changed as a result of longstanding or recent introductions of new pathogens. From this it can be inferred that as a result of international trade the main threat for forests is the entry of alien pests whose expression (establishment, emergence, epidemic, etc.) is possibly boosted by ongoing climate change

Effets combinés de la sécheresse et de la fertilisation sur les nécroses corticales induites par Sphaeropsis sapinea

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