Is the Emergence of Dothistroma Needle Blight of Pine in France Caused by the Cryptic Species Dothistroma pini?

International audienceDothistroma needle blight (DNB) emerged in France in the past 15 years. This disease is induced by two closely related species Dothistroma septosporum and D. pini. While both species are nowadays present in France, only D. septosporum was reported in the past. We investigated whether a recent arrival of D. pini in France could be a cause of the DNB emergence. We analysed herbarium specimens of pine needle with DNB symptoms using PCR techniques to study the past frequency of D. pini in France. We also determined the present distribution within the country of D. septosporum and D. pini and compared it to the spatial pattern of DNB report in the DSF data base (french forest health monitoring agency). Although D. pini was detected on herbarium specimens from 1907 and 1965, it was not frequent in France in the past. It is nowadays frequent although not present throughout the country, being absent from the north and the east. There is no relationship between the D. pini distribution in France and the spatial pattern of DNB report in the DSF database. Thus, the emergence of DNB in France cannot be explained by a recent arrival of D. pini

Assessment of inoculation methods for screening black alder resistance to Phytophthora ×alni

International audienceIdentification of resistance to Phytophthora ×alni could provide the basis for a management strategy against alder decline in riparian ecosystems in Europe. Our objectives were to test methods to evaluate the resistance of riparian alders to the disease, and to screen alder genotypes for resistance. P. ×alni isolates were compared for their stability in collection, aggressiveness (lesion length on stem) and sporulation capacity (sporangia). While no difference of lesion lengths was found between P. ×alni isolates, sporangia production was dependent on isolate, highlighting the need to select carefully isolates for inoculation methods dealing with zoospores suspension. Inoculation tests carried out at different periods of the year revealed a seasonal change in susceptibility to the disease, with the period from June to September being the most efficient for inoculation tests. Stem-wounded inoculations tests carried out on excised shoots were found unreliable for evaluating the level of resistance of alder genotypes to P. ×alni infection, with divergent results between two successive years or between two inoculation periods during the same year. In contrast, a method which mimics the natural conditions of infection based on flooding of rooted cuttings in artificially infected river water was found promising. Another method based on the inoculation of foliated terminal shoots with zoospore suspensions was found to be repeatable and could be used for high throughput analyses. Altogether, the results show a continuous resistance response from highly susceptible to moderately resistant genotypes. This suggests that breeding might be a useful strategy to manage alder decline caused by P. ×alni

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

Honaïn

Sur la côte d’Oranie, à 52 kilomètres de la frontière marocaine, se creuse une baie à laquelle des hauteurs escarpées donnent des allures de fjord. Une plage en occupe le fond et, derrière la plage, l’enceinte d’une ville se dessine, escaladant les pentes de la montagne. Cette ville, ou plutôt cette coquille de ville vidée de son contenu, c’est Honaïn, dont le nom figure à maintes reprises chez les chroniqueurs et les géographes du Moyen Âge. Nul centre antique ne paraît l’avoir précédée, à m..

Honaïn

Sur la côte d’Oranie, à 52 kilomètres de la frontière marocaine, se creuse une baie à laquelle des hauteurs escarpées donnent des allures de fjord. Une plage en occupe le fond et, derrière la plage, l’enceinte d’une ville se dessine, escaladant les pentes de la montagne. Cette ville, ou plutôt cette coquille de ville vidée de son contenu, c’est Honaïn, dont le nom figure à maintes reprises chez les chroniqueurs et les géographes du Moyen Âge. Nul centre antique ne paraît l’avoir précédée, à m..

Facteurs édaphiques, dépérissement du chêne et infection par Collybia fusipes

International audienceCollybia fusipes is the cause of a root rot of oaks in Europe. Infection by the pathogen is site dependent and inconsistently correlated with crown deterioration. This study aimed at clarifying the relationship between soil factors and C. fusipes impact on tree health. The database of the Département de la Santé des Forêts, the forest health survey service, collected over the French forest during the last 12 years allowed us to perform a large scale study dealing with soil textures in which C. fusipes was reported to induce problems on Quercus robur and/or Q. petraea. Furthermore, a specific survey from 30 plots in north eastern France was carried out to determine which of the soil factors, such as texture, degree of waterlogging, presence and nature of a layer limiting rooting, carbon/nitrogen ratio, cation exchange capacity, or pH could be related to an increased risk of decline of pedunculate oaks infected by C. fusipes. The main results were that C. fusipes is preferentially distributed on coarse textured soils and that its impact on tree crown appearance also increased with the soil sand content

Honaïn

Sur la côte d’Oranie, à 52 kilomètres de la frontière marocaine, se creuse une baie à laquelle des hauteurs escarpées donnent des allures de fjord. Une plage en occupe le fond et, derrière la plage, l’enceinte d’une ville se dessine, escaladant les pentes de la montagne. Cette ville, ou plutôt cette coquille de ville vidée de son contenu, c’est Honaïn, dont le nom figure à maintes reprises chez les chroniqueurs et les géographes du Moyen Âge. Nul centre antique ne paraît l’avoir précédée, à m..