Rising out of the ashes: Additive genetic variation for crown and collar resistance to Hymenoscyphus fraxineus in Fraxinus excelsior

Since the early 1990s, ash dieback due to the invasive ascomycete Hymenoscyphus fraxineus is threatening Fraxinus excelsior in most of its natural range. Previous studies reported significant levels of genetic variability in susceptibility in F. excelsior either in field or inoculation experiments. The present study was based on a field experiment planted in 1995, 15 years before onset of the disease. Crown and collar status were monitored on 777 trees from 23 open-pollinated progenies originating from three French provenances. Health status was modeled using a Bayesian approach where spatiotemporal effects were explicitly taken into account. Moderate narrow-sense heritability was found for crown dieback (h2 = 0.42). This study is first to show that resistance at the collar level is also heritable (h2 = 0.49 for collar lesions prevalence and h2 = 0.42 for their severity) and that there is significant genetic correlation (r = 0.40) between the severities of crown and collar symptoms. There was no evidence for differences between provenances. Family effects were detected, but computing individual breeding values showed that most of the genetic variation lies within families. In agreement with previous reports, early flushing correlates with healthier crown. Implications of these results in disease management and breeding are discussed

Advanced spectroscopy-based phenotyping offers a potential solution to the ash dieback epidemic

Natural and urban forests worldwide are increasingly threatened by global change resulting from human-mediated factors, including invasions by lethal exotic pathogens. Ash dieback (ADB), incited by the alien invasive fungus Hymenoscyphus fraxineus, has caused large-scale population decline of European ash (Fraxinus excelsior) across Europe, and is threatening to functionally extirpate this tree species. Genetically controlled host resistance is a key element to ensure European ash survival and to restore this keystone species where it has been decimated. We know that a low proportion of the natural population of European ash expresses heritable, quantitative resistance that is stable across environments. To exploit this resource for breeding and restoration efforts, tools that allow for effective and efficient, rapid identification and deployment of superior genotypes are now sorely needed. Here we show that Fourier-transform infrared (FT-IR) spectroscopy of phenolic extracts from uninfected bark tissue, coupled with a model based on soft independent modelling of class analogy (SIMCA), can robustly discriminate between ADB-resistant and susceptible European ash. The model was validated with populations of European ash grown across six European countries. Our work demonstrates that this approach can efficiently advance the effort to save such fundamental forest resource in Europe and elsewhere

Characterization of two major genetic factors controlling quantitative resistance to Melampsora larici-populina leaf rust in hybrid poplars : strain specificity, field expression, combined effects, and relationship with a defeated qualitative resistance gene

International audienceTwo genetic factors explain a significant proportion of the variability for quantitative resistance to Melampsora larici-populina leaf rust in a Populus deltoides × P. trichocarpa F1 progeny. One is inherited from P. deltoides and is associated with a defeated qualitative resistance gene R1, and the other, RUS, is inherited from P. trichocarpa. To assess the potential contribution of these two factors for durable resistance breeding, 284 genotypes from this F1 progeny were studied in laboratory experiments with three M. larici-populina strains and in a field experiment under natural inoculum pressure. Results confirmed that both factors can have strong beneficial effects in the laboratory. These effects were strain specific, thus impairing their chances for durability. However, association of both factors led to synergistic effects in most situations. In accordance with good field–laboratory relationships, especially those involving uredinia-size laboratory measurements, field effects of both resistance factors were significant. RUS led to a significant reduction of rust colonization on the most infected leaf in the field, and its effect was significant both in the presence and the absence of R1. In contrast, the presence of R1 was useful in the field only when RUS was absent. The nature of the genetic relationship between both factors remains unknown, but benefits from their association should be quantified over a longer period to evaluate potential adaptation of the pathogen

Characterization of two major genetic factors controlling quantitative resistance to Melampsora larici-populina leaf rust in hybrid poplars : strain specificity, field expression, combined effects, and relationship with a defeated qualitative resistance gene

Two genetic factors explain a significant proportion of the variability for quantitative resistance to Melampsora larici-populina leaf rust in a Populus deltoides × P. trichocarpa F1 progeny. One is inherited from P. deltoides and is associated with a defeated qualitative resistance gene R1, and the other, RUS, is inherited from P. trichocarpa. To assess the potential contribution of these two factors for durable resistance breeding, 284 genotypes from this F1 progeny were studied in laboratory experiments with three M. larici-populina strains and in a field experiment under natural inoculum pressure. Results confirmed that both factors can have strong beneficial effects in the laboratory. These effects were strain specific, thus impairing their chances for durability. However, association of both factors led to synergistic effects in most situations. In accordance with good field–laboratory relationships, especially those involving uredinia-size laboratory measurements, field effects of both resistance factors were significant. RUS led to a significant reduction of rust colonization on the most infected leaf in the field, and its effect was significant both in the presence and the absence of R1. In contrast, the presence of R1 was useful in the field only when RUS was absent. The nature of the genetic relationship between both factors remains unknown, but benefits from their association should be quantified over a longer period to evaluate potential adaptation of the pathogen

Spatio-temporal model for the genetic resistance to ash-dieback

Ash-dieback is an invasive fungal disease of ash trees characterised by leaf loss and crown dieback in infected trees. First detected in Poland in the early 1990s, it rapidly progressed throughout Europe causing large numbers of deaths and threatening today the survival of the species. We modelled the evolution of the disease from 2010 to 2014 within a field experiment located in northern France, with 777 trees from 23 progenies originating from three french provenances. The objective was to assess the genetic (co)variation associated with two different symptoms: _Crown Dieback_ (CD) and _Collar Lesion_ (CL), since this has direct implications for breeding and for the management of the disease. Due to a high proportion of non-symptomatic observations of CL we used a mixture Binomial-Gamma for modelling the probability of infection and its conditional severity separately at the data level. For CD and both components of CL, a latent gaussian field accounted for some specific relevant covariates, the temporal global trend, the genetic effects and a spatio-temporal structure that represented the regionalized relative exposure to pathogen agent

Analyse génétique de la résistance et de la tolérance de peupliers hybrides Populus deltoides x Populus trichocarpa à la rouille foliaire à Melampsora larici-populina

ORLEANS-BU Sciences (452342104) / SudocSudocFranceF

Presence of defeated qualitative resistance genes frequently has major impact on quantitative resistance to Melampsora larici-populina leaf rust in P.xinteramericana hybrid poplars

International audienceQualitative resistance to Melampsora larici-populina leaf rust inherited from North American species Populus deltoides did not allow for durable control of this pathogen in interspecific hybrid cultivars. Despite significant levels of strain-specificity, quantitative resistance would exert lower selection pressures on the pathogen populations, and hence could be more durable. Previous studies restricted to a large P. × interamericana (i.e., P. deltoides × Populus trichocarpa) F1 family revealed that the presence of R1, a segregating defeated qualitative resistance gene inherited from P. deltoides, had major beneficial effects on quantitative resistance. The present study was based on 14 F1 families from a 4 × 5 P. deltoides × P. trichocarpa factorial mating design where at least four defeated qualitative resistances segregate 1:1. Even though quantitative resistance assessments were conducted in the laboratory with a M. larici-populina strain able to overcome these qualitative resistances, their presence had a significant effect on the mean level and on the genetic variability for quantitative resistance. One unprecedented result is the identification of a defeated qualitative resistance which presence is associated with lower levels of quantitative resistance. Possible inferences on the nature of the genetic relationship between both resistance types are discussed

Fraxinus dieback in Europe: elaborating guidelines and strategies for sustainable managementies for sustainable management (FRAXBACK)

Memorandum of Understanding for the implementation of the European Concerted Research Action FP1103Currently, severe dieback of Fraxinus spp. is observed in most European countries. This is an emerging disease, which results in massive tree mortality, threatening the existence of Fraxinus over the continent. It is caused by Hymenoscyphus pseudoalbidus, alien and invasive fungus, origin of which remains unknown. Currently, many European countries have national research programs on Fraxinus dieback, focusing on numerous aspects of the biology and ecology of the disease, but the activities are scattered. Aim of the FRAXBACK is, through sharing and synthesis of available knowledge, generate comprehensive understanding of Fraxinus dieback phenomenon, and to elaborate state of the art practical guidelines for sustainable management of Fraxinus in Europe. The Action will be implemented through innovative interdisciplinary approach, and will include forest pathologists, tree breeders and silviculturists. Its deliverables: i) guidelines for sustainable management of Fraxinus in Europe; ii) European database for dieback-resistant Fraxinus genotypes/families/populations and established/planned progeny trials; iii) illustrated digests/leaflets/brochures on Fraxinus dieback; iv) disease distribution maps; v) website; vi) book. FRAXBACK is comprised of four Working Groups: WG1 Pathogen; WG2 Host; WG3 Silviculture; WG4 Dissemination and knowledge gaps. Its duration is 4 years, including two MC/WG meetings and four STSMs per year, and one international conference

Un arbre précieux : le peuplier

National audienceLe récent décryptage de son génome va permettre des avancées considérables dans les domaines de la sylviculture, de l’écologie et de la gestion des milieux forestiers