Highlights• First report of mycoviruses isolated from fungi from marine environment.• Survey of mycoviruses using multiple approaches for both DNA and RNA genomes.• RNAseq analysis is superior to sRNA for de novo assembly of mycoviruses.• Twelve new virus species were characterized molecularly.• Expression of a viral RNA from an endogenized cDNA segment. AbstractThe number of reported mycoviruses is increasing exponentially due to the current ability to detect mycoviruses using next-generation sequencing (NGS) approaches, with a large number of viral genomes built in-silico using data from fungal transcriptome projects. We decided to screen a collection of fungi originating from a specific marine environment (associated with the seagrass Posidonia oceanica) for the presence of mycoviruses: our findings reveal a wealth of diversity among these symbionts and this complexity will require further studies to address their specific role in this ecological niche. In specific, we identified twelve new virus species belonging to nine distinct lineages: they are members of megabirnavirus, totivirus, chrysovirus, partitivirus and five still undefined clades. We showed evidence of an endogenized virus ORF, and evidence of accumulation of dsRNA from metaviridae retroviral elements. We applied different techniques for detecting the presence of mycoviruses including (i) dsRNA extraction and cDNA cloning, (ii) small and total RNA sequencing through NGS techniques, (iii) rolling circle amplification (RCA) and total DNA extraction analyses, (iv) virus purifications and electron microscopy. We tried also to critically evaluate the intrinsic value and limitations of each of these techniques. Based on the samples we could compare directly, RNAseq analysis is superior to sRNA for de novo assembly of mycoviruses. To our knowledge this is the first report on the virome of fungi isolated from marine environment.

This research illustrates the qualitative and quantitative composition of the mycoflora of both a green compost (thermophilically produced from plant debris) and a vermicompost (mesophilically produced by the action of earthworms on plant and animal wastes after thermophilic preconditioning). Fungi were isolated using three media (PDA, CMC, PDA plus cycloheximide), incubated at three temperatures (24, 37 and 45 C). Substantial qualiquantitative differences in the species composition of the two composts were observed. The total fungal load was up to 8.2 X 10(5) CFU/g dwt in compost and 4.0 x 10(5) CFU/g dwt in vermicompost. A total of 194 entities were isolated: 118 from green compost, 142 from vermicompost; 66 were common to both. Structural characterization of this kind is necessary to determine the most appropriate application of a compost and its hygienic quality.

In order to study the influence of Arbuscular Mycorrhiza (AM) on the development of root rot infection, tomato plants were raised with or without Glomus mosseae and/or Phytophthora nicotianae var. parasitica in a sand culture system. All plants were fed with a nutrient solution containing one of two phosphorus (P) levels, 32 #M (I P) or 96 #M (IIP), to test the consequence of enhanced P nutrition by the AM fungus on disease dynamics. Mycorrhizal plants had a similar development to that of control plants. Treatment with Phytophthora nicotianae var. parasitica resulted in a visible reduction in plant weight and in a widespread root necrosis in plants without mycorrhiza. The presence of the AM fungus decreased both weight reduction and root necrosis. The percentage reduction of adventitious root necrosis and of necrotic root apices ranged between 63 and 89% The enhancement of P nutrition increased plant development, but did not appreciably decrease disease spread. In our system, mycorrhiza increased plant resistance to P. nicotianae var. parasitica infection. Although a contribution of P nutrition by mycorrhiza cannot be excluded, other mechanisms appear to play a crucial role.Abbreviations: AM -arbuscular mycorrhizae, G-Phy--plants without G. mosseae nor P. nicotianae var. parasitica, G + Phy--plants with G. mosseae but without P. nicotianae var. parasitica, G-Phy + -plants without G. mosseae but with R nicotianae var. parasitica, G + Phy + -plants with both G. mosseae and P nicotianae var. parasitica, I P -first phosphorus level (32 #M), IIP -second phosphorus level (96/zM).

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In Europe the forest pathogen Heterobasidion annosum (Fr.) Bref. includes the S, P, and F intersterility groups (ISGs), each displaying a preferential specialization on Norway spruce (Picea abies (L.) Karst.), pine, and silver fir (Abies alba Mill.), respectively. In this paper, we present data about (i) H. annosum ISGs frequency in different forest types, (ii) the degree of host specificity of each ISG, (iii) the significance of the potential movement of airborne spores among forests, and (iv) the occurrence of S–P chimeras in the northwestern Alps. Using woody spore traps, we sampled natural pure spruce and fir forests and a mixed spruce-fir forest. The ISG of 582 spores was determined by ISG-diagnostic taxon-specific competitive priming (TSCP) polymerase chain reaction (PCR) combined with PCR-mediated detection of ISG-specific introns in the ML5–ML6 DNA region of the mitochondrial large ribosomal RNA (mt LrRNA). All three ISGs were found, and a strong correlation was observed between the F ISG and fir and the S ISG and spruce. In the mixed forest, no clear relationship between tree host species and host-specialized ISGs was found. In spite of a relative dominance of fir in the overstory of the mixed stand, the fir-associated F ISG represented only 11% of the total number of spores collected. This discrepancy was explained by the recent establishment of firs at this site. No S–P nuclear-mitochondrial chimeras were found. This suggests limited gene flow between these ISGs.Key words: Heterobasidion annosum, host specificity, ISGs, gene flow, PCR, Alps.