Genetic diversity and origins of the homoploid allopolyploid hybrid Phytophthora× alni. J Aguayo, F Halkett, C Husson, ZÁ Nagy, A Szigethy, J Bakonyi, P Frey, … Applied and Environmental Microbiology, AEM. 02221-16

Abstract

Soil type determines the distribution of nutrient mobilizing bacterial communities in the rhizosphere of beech trees O Nicolitch, Y Colin, MP Turpault, S Uroz. Soil Biology and Biochemistry 103, 429-445

Abstract

Rhizosphere represents a nutrient-rich environment and a hotspot of bacterial activities compared to the surrounding bulk soil. However, few studies have investigated how this rhizosphere effect depends on the soil conditions, and never for trees. Contrary to annual plants, trees need decades to grow and strongly depend on the access and recycling of soil nutrients and water. In this context, we aimed at understanding if contrasted soil types impact the taxonomy and functions of bacterial communities inhabiting beech rhizosphere. To test this hypothesis, we considered the natural toposequence of Montiers, which is characterized by a same land cover dominated by beech (Fagus sylvatica) trees of the same age, growing under the same climatic conditions and under the same forestry practices. We used a combination of in vitro bioassays and 16S rRNA gene sequences analyses on a collection of 370 bacterial strains generated from beech rhizosphere and surrounding bulk soil samples collected in the organo-mineral horizon along the toposequence. Our study highlighted an increasing beech rhizosphere effect from the nutrient-rich to nutrient-poor soils, with specific bacterial functions related to inorganic nutrient mobilization largely and exclusively enriched in the rhizosphere of the nutrient-poor soils. This functional selection in the rhizosphere came with an enrichment of bacterial strains assigned to the Burkholderia and Collimonas genus, which appeared to be the dominant and most effective mineral-weathering bacteria. Our data corroborate the hypothesis of a variable selection of specific rhizosphere bacterial communities by beech trees according to the soil conditions and the tree nutritional requirements.

Root-endophytic fungi cause morphological and functional differences in Scots pine roots in contrast to ectomycorrhizal fungi. J Heinonsalo, M Buée, LM Vaario. Botany

RÉSUMÉ

Investigation of the sexual reproduction strategy of the Perigord black truffle (tuber melanosporum Vittad.) revealed trioecy. H De la Varga, F Le Tacon, M Lagoguet, F Todesco, T Varga, I Miquel, …Bio-archive

Abstract

Fungi display a rich variety of sexual reproduction systems and are therefore good models to investigate sex evolution. Moreover, understanding the investment in sexual reproduction of edible fungi is a critical challenge for improving their cultivation. The Perigord black truffle (Tuber melanosporum Vittad.) is a heterothallic ascomycete associated with trees through ectomycorrhizas and forming highly prized ascocarps. The aim of this study was to unravel the sexual reproduction strategy (hermaphroditic versus male/female specialization) of T. melanosporum in a truffle orchard by disentangling the contribution of female and male genotypes to the formation of ascocarps in a five-year investigation. Few genotypes were hermaphrodites, co-occurring with numerous genotypes behaving only as female or male, revealing trioecy. The genetic diversity of the male genotypes was higher than female diversity, suggesting for male elements a higher recruitment from ascospores. Most of the female and male genotypes were transitory (present only one year), whereas some genotypes persisted for several years: female-fertile genotypes as mycorrhizas, and male-fertile genotypes as soil free-living mycelium. Contrary to other ascomycetes, a high number of female-fertile only genotypes was found. We hypothesized that the mycorrhizal life style favours female-fertile strains and therefore that the life strategy influences fungal sexual strategy.

Global geographic distribution and host range of Dothistroma species: a comprehensive review R Drenkhan, V Tomešová‐Haataja, S Fraser, RE Bradshaw, P Vahalík, … Forest Pathology

Summary

Dothistroma needle blight (DNB) is one of the most important diseases of pine. Although its notoriety stems from Southern Hemisphere epidemics in Pinus radiataplantations, the disease has increased in prevalence and severity in areas of the Northern Hemisphere, including Europe, during the last two decades. This increase has largely been attributed to expanded planting of susceptible hosts, anthropogenic dispersal of the causative pathogens and changes in climate conducive to disease development. The last comprehensive review of DNB was published in 2004, with updates on geographic distribution and host species in 2009. Importantly, the recognition that two species, Dothistroma septosporum and D. pini, cause DNB emerged only relatively recently in 2004. These two species are morphologically very similar, and DNA-based techniques are needed to distinguish between them. Consequently, many records of host species affected or geographic location of DNB prior to 2004 are inconclusive or even misleading. The objectives of this review were (i) to provide a new database in which detailed records of DNB from 62 countries are collated; (ii) to chart the current global distribution of D. septosporum and D. pini; (iii) to list all known host species and to consider their susceptibility globally; (iv) to collate the published results of provenance trials; and (v) to consider the effects of site factors on disease incidence and severity. The review shows that DNB occurs in 76 countries, with D. septosporum confirmed to occur in 44 and D. pini in 13. There are now 109 documented Pinaceae host taxa for Dothistroma species, spanning six genera (Abies, Cedrus, Larix, Picea, Pinus and Pseudotsuga), with Pinus being the dominant host genus, accounting for 95 host taxa. The relative susceptibilities of these hosts to Dothistroma species are reported, providing a resource to inform species choice in forest planting. Country records show that most DNB outbreaks in Europe occur on Pinus nigra and its subspecies. It is anticipated that the collaborative work described in this review will both underpin a broader global research strategy to manage DNB in the future and provide a model for the study of other forest pathogens.

Diversity and Structure of Fungal Communities in Neotropical Rainforest Soils: The Effect of Host Recurrence H Schimann, C Bach, J Lengelle, E Louisanna, S Barantal, C Murat, … Microbial Ecology, 1-11

Abstract

The patterns of the distribution of fungal species and their potential interactions with trees remain understudied in Neotropical rainforests, which harbor more than 16,000 tree species, mostly dominated by endomycorrhizal trees. Our hypothesis was that tree species shape the non-mycorrhizal fungal assemblages in soil and litter and that the diversity of fungal communities in these two compartments is partly dependent on the coverage of trees in the Neotropical rainforest. In French Guiana, a long-term plantation and a natural forest were selected to test this hypothesis. Fungal ITS1 regions were sequenced from soil and litter samples from within the vicinity of tree species. A broad range of fungal taxa was found, with 42 orders and 14 classes. Significant spatial heterogeneity in the fungal communities was found without strong variation in the species richness and evenness among the tree plots. However, tree species shaped the fungal assemblages in the soil and litter, explaining up to 18 % of the variation among the communities in the natural forest. These results demonstrate that vegetation cover has an important effect on the structure of fungal assemblages inhabiting the soil and litter in Amazonian forests, illustrating the relative impact of deterministic processes on fungal community structures in these highly diverse ecosystems.

Ectomycorrhizal ecology is imprinted in the genome of the dominant symbiotic fungus Cenococcum geophilum M Peter, A Kohler, RA Ohm, A Kuo, J Krützmann, E Morin, M Arend, … Nature Communications 7, 12662

Abstract

The most frequently encountered symbiont on tree roots is the ascomycete Cenococcum geophilum,the only mycorrhizal species within the largest fungal class Dothideomycetes, a class known for devastating plant pathogens. Here we show that the symbiotic genomic idiosyncrasies of ectomycorrhizal basidiomycetes are also present in C. geophilum with symbiosis-induced, taxon-specific genes of unknown function and reduced numbers of plant cell wall-degrading enzymes. C. geophilum still holds a significant set of genes in categories known to be involved in pathogenesis and shows an increased genome size due to transposable elements proliferation. Transcript profiling revealed a striking upregulation of membrane transporters, including aquaporin water channels and sugar transporters, and mycorrhiza-induced small secreted proteins (MiSSPs) in ectomycorrhiza compared with free-living mycelium. The frequency with which this symbiont is found on tree roots and its possible role in water and nutrient transport in symbiosis calls for further studies on mechanisms of host and environmental adaptation.

Improving the design of long-term monitoring experiments in forests: a new method for the assessment of local soil variability by combining infrared spectroscopy and dendrometric data E Akroume, B Zeller, M Buée, P Santenoise, L Saint-André Annals of Forest Science, 1-9

Genetic signatures of a range expansion in natura: when clones play leapfrog R Becheler, C Xhaard, EK Klein, KJ Hayden, P Frey, S De Mita, F Hackett. Ecology and Evolution

Abstract