Impact of Erysiphe alphitoides on transpiration and photosynthesis in Quercus robur leaves

International audienceOak powdery mildew, (Erysiphe alphitoides) causes one of the most common diseases of oaks. We assessed the impact of this pathogen on photosynthesis and water relations of infected leaves using greenhouse grown oak seedlings. Transpiration of seedling infected by oak powdery mildew was also investigated. Altogether, E. alphitoides had a low impact on host gas exchange whether at leaf or whole plant scale. Maximal stomatal conductance of infected leaves was reduced by 20-30% as compared to healthy controls. Severely infected seedlings did not experience any detectable change of whole plant transpiration. The reduction in net CO 2 assimilation, A n , was less than proportional to the fraction infected leaf area. Powdery mildew reduced both the maximal light driven electron flux (J max) and the apparent maximal carboxylation velocity (Vc max) although Vc max was slightly more impacted than J max. No compensation of the infection occurred in healthy leaves of partly infected seedlings as the reduced photosynthesis in the infected leaves was not paralleled by increased A n levels in the healthy leaves of the seedlings. However, E. alphitoides had a strong impact on leaf lifespan of infected leaves. It is concluded that the moderate effect of E. alphitoides on oak might be related to the small impact on net CO 2 assimilation rates and on tree transpiration; nevertheless, the severe reduction in leaf lifespan of heavily infected leaves may lead to decreased carbon uptake over the growth season

Influence of site and stand factors on Hymenoscyphus fraxineus-induced basal lesions

Hymenoscyphus fraxineus is an invasive fungus in Europe and causes a severe decline affecting ash, which began in the late 1990s. One of the symptoms associated with the disease is lesions in the outer bark of the collar area. However, the aetiology of these basal lesions, and in particular the relative roles of H.fraxineus and Armillaria species, is still controversial; moreover, little is known about the influence of environmental factors on the disease epidemiology.This study therefore surveyed 42 plots located in northeastern France, in an area affected by ash decline since 2008, in order to determine which environmental factors condition the severity of lesions associated with H.fraxineus on ash collar. The spatial pattern that is a consequence of the invasive spread of the disease was taken into account in the analysis, using a spatial hierarchical Bayesian model fitted by integrated nested laplace approximation (INLA).Results show that while basal lesions are tightly associated with H.fraxineus, their severity is influenced by the Armillaria species present in the plot. Sites with vegetation indicating moist conditions, or more humid topographical positions, were associated with more developed basal lesions

Population structure and diversity of the needle pathogen Dothistroma pini suggests human-mediated movement in Europe

Dothistroma needle blight (DNB) is an important disease of Pinus species that can be caused by one of two distinct but closely related pathogens; Dothistroma septosporum and Dothistroma pini. Dothistroma septosporum has a wide geographic distribution and is relatively well-known. In contrast, D. pini is known only from the United States and Europe, and there is a distinct lack of knowledge regarding its population structure and genetic diversity. The recent development of 16 microsatellite markers for D. pini provided an opportunity to investigate the diversity, structure, and mode of reproduction for populations collected over a period of 12 years, on eight different hosts in Europe. In total, 345 isolates from Belgium, the Czech Republic, France, Hungary, Romania, Western Russia, Serbia, Slovakia, Slovenia, Spain, Switzerland, and Ukraine were screened using microsatellite and species-specific mating type markers. A total of 109 unique multilocus haplotypes were identified and structure analyses suggested that the populations are influenced by location rather than host species. Populations from France and Spain displayed the highest levels of genetic diversity followed by the population in Ukraine. Both mating types were detected in most countries, with the exception of Hungary, Russia and Slovenia. Evidence for sexual recombination was supported only in the population from Spain. The observed population structure and several shared haplotypes between non-bordering countries provides good evidence that the movement of D. pini in Europe has been strongly influenced by human activity in Europe

Population structure and diversity of the needle pathogen Dothistroma pini suggests human-mediated movement in Europe

DATA AVAILABILITY STATEMENT : The authors acknowledge that the data presented in this study must be deposited and made publicly available in an acceptable repository, prior to publication. Frontiers cannot accept a manuscript that does not adhere to our open data policies.Dothistroma needle blight (DNB) is an important disease of Pinus species that can be caused by one of two distinct but closely related pathogens; Dothistroma septosporum and Dothistroma pini. Dothistroma septosporum has a wide geographic distribution and is relatively well-known. In contrast, D. pini is known only from the United States and Europe, and there is a distinct lack of knowledge regarding its population structure and genetic diversity. The recent development of 16 microsatellite markers for D. pini provided an opportunity to investigate the diversity, structure, and mode of reproduction for populations collected over a period of 12 years, on eight different hosts in Europe. In total, 345 isolates from Belgium, the Czech Republic, France, Hungary, Romania, Western Russia, Serbia, Slovakia, Slovenia, Spain, Switzerland, and Ukraine were screened using microsatellite and species-specific mating type markers. A total of 109 unique multilocus haplotypes were identified and structure analyses suggested that the populations are influenced by location rather than host species. Populations from France and Spain displayed the highest levels of genetic diversity followed by the population in Ukraine. Both mating types were detected in most countries, with the exception of Hungary, Russia and Slovenia. Evidence for sexual recombination was supported only in the population from Spain. The observed population structure and several shared haplotypes between non-bordering countries provides good evidence that the movement of D. pini in Europe has been strongly influenced by human activity in Europe.The University of Pretoria, members of the Tree Protection Cooperative Program (TPCP), the National Research Foundation, a Scarce Skills Doctoral Scholarship and DIAROD: EU COST Action FP1102 DIAROD.http://www.frontiersin.org/Geneticsam2024BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant PathologySDG-15:Life on lan

Influence de facteurs de l'environnement sur le developpement de l'encre du chene rouge (Quercus rubra L.), maladie provoquee par Phytophthora cinnamoni

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 84428 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Role of an opportunistic pathogen in the decline of stressed oak trees

1 The importance of opportunistic pathogens, in particular Armillaria species, in forest decline has often been open to debate. 2 In order to assess the role of Armillaria gallica in the decline of oak trees, 60 Quercus robur trees with high (HIP trees) or low (LIP trees) levels of A. gallica inoculum, as measured by the density of epiphytic rhizomorphs on the root collar, were artificially defoliated for 2 years. Half of the HIP trees were treated when first defoliated with boric acid to reduce the A. gallica inoculum potential (BHIP trees). The ability of in situ rhizomorphs to colonize plant material was similar for LIP and BHIP, but was lower than in HIP trees, indicating that the boric acid treatment reduced the level of A. gallica inoculum. 3 Tree growth was similar between treatments as determined by dendrochronological comparisons. Although defoliation greatly reduced both tree growth and sapwood starch reserves at the beginning of autumn, growth response to defoliation and sapwood starch concentration at the beginning of autumn were similar for LIP, BHIP and HIP trees. 4 HIP trees suffered considerably greater crown deterioration and mortality following defoliation than either BHIP or LIP trees (62%, 32% and 5% mortality rates, respectively). The trees that died had very low sapwood starch concentrations. In addition, at similar levels of sapwood starch, HIP trees were much more likely to die than LIP or BHIP trees. 5 Two other factors influenced tree mortality. Past stress that reduced the tree growth a few years prior to the start of the experiment was shown to alter the tree’s ability to cope with defoliation. Oak mildew selectively infected the defoliated trees and increased the severity of the defoliation stress. 6 Thus, trees subjected to high level of A. gallica inoculum had a lower ability to overcome the defoliation stress. These findings support the forest decline models developed by Manion in 1991 and show that it is important to take into account the role of opportunistic pathogens in tree mortality processes

Relation between <i>Collybia fusipes</i> root rot and growth of pedunculate oak

International audienceCollybia fusipes (Bull. ex Fr.) is the cause of a root rot on oak, mainly pedunculate oak, Quercus robur L., and northern red oak, Quercus rubra L. The disease is associated with a deterioration of the crown of affected trees in some, but not all, stands. We investigated the relationship between the level of root damage induced by C. fusipes and past growth of the infected trees at four sites of pedunculate oaks and one site of red oaks in northeastern and central France. The severely infected oaks showed poor growth for 15-50 years depending on the site. At one site where C. fusipes was not associated with a deterioration of the affected tree crowns, the basal area increments of severely root damaged oaks has nevertheless been poor for more than 30 years. Severe infection by C. fusipes was associated with a 30-50% reduction of basal area increment in the last 10 years preceding the study at all the sites. In contrast, in all the sites, trees lightly damaged by C. fusipes had basal area increments similar to the undamaged trees. The data would be consistent with a disease that develops slowly on vigorous trees and affects their growth only late in the infection process.Collybia fusipes (Bull. ex Fr.) provoque un pourridié chez les chênes, en particulier les chênes pédonculé, Quercus robur L., et rouge, Quercus rubra L. La maladie n'est pas associée à une dégradation du houppier des arbres infectés dans tous les peuplements atteints. Nous avons étudié la relation entre le degré d'infection du système raci-naire et la croissance passée des arbres infectés dans quatre peuplements de chêne pédonculé et un peuplement de chêne rouge dans le nord-est et le centre de la France. Les chênes sévèrement infectés avaient une croissance faible de-puis 15 à 50 ans selon le peuplement. À Amance, où C. fusipes n'est pas associé à une détérioration du houppier des arbres infectés, l'accroissement en surface terrière des arbres à système racinaire fortement dégradé était faible depuis plus de 30 ans. Quelque soit le peuplement, une forte attaque par C. fusipes était associée à une réduction de l'accroissement en surface terrière de 30-50% dans les 10 ans précédant l'étude. Par contre, dans tous les peuplements, les arbres faiblement infectés par la collybie avaient un accroissement en surface terrière similaire à celui des arbres non infectés. Les résultats indiqueraient que le pourridié à collybie est une maladie se développant lentement sur les abres vigoureux et n'affectant leur croissance des arbres que tard dans le processus d'infection

Genetic characterization of the natural hybrid species Phytophthora alni as inferred from nuclear and mitochondrial DNA analyses

The diVerent subspecies of Phytophthora alni, P. alni subsp. alni (Paa), P. alni subsp. uniformis (Pau), and P. alni subsp. multiformis (Pam), are recent and widespread pathogens of alder in Europe. They are believed to be a group of emergent heteroploid hybrids between two phylogenetically close Phytophthora species. Nuclear and mitochondrial DNA analyses were performed, using a broad collection of P. alni and two closely related species, P. cambivora and P. fragariae. Paa possesses three diVerent alleles for each of the nuclear genes we studied, two of which are present in Pam as well, whereas the third matches the single allele present in Pau. Moreover, Paa displays common mtDNA patterns with both Pam and Pau. A combination of the data suggests that Paa may have been generated on several occasions by hybridization between Pam and Pau, or their respective ancestors. Pau might have P. cambivora as a species ancestor, whereas Pam seems to have either been generated itself by an ancient reticulation or by autopolyploidization. © 2006 Elsevier Inc. All rights reserve

La chalarose du frêne en France

La chalarose, en progression vers l'ouest et le sud, entraîne le dépérissement de frênes en France. Les niveaux de dépérissement ou mortalité dépendent de la résistance génétique de l'individu, de son âge et de l'environnement. Après l'arrêt des plantations, il est recommandé de préserver les frênes peu dépérissants ; ils constitueront un réservoir d'individus résistants à la maladie