Interactions between engineered tomato plants expressing antifungal enzymes and nontarget fungi in the rhizosphere and phyllosphere.

The introduction of genetically modified (GM) plants in agroecosystems raises concern about possible effects on nontarget species. The impact of a tomato line transformed for constitutive expression of tobacco beta-1,3-glucanase and chitinase on indigenous nonpathogenic fungi was investigated. In greenhouse experiments, no significant differences were found in the colonization by arbuscular mycorrhizal fungi. Diversity indices computed from over 20 500 colonies of culturable rhizosphere and phyllosphere saprotrophic microfungi, assigned to 165 species (plus > 80 sterile morphotypes), showed no significant differences between GM and wild-type plants. Differences were found by discriminant analysis in both the rhizosphere and the phyllosphere, but such effects were minor compared with those linked to different plant growth stages.

Soil persistence and biodiversity of ericoid mycorrhizal fungi in the absence of the host plant in a Mediterranean ecosystem.

The occurrence of suitable mycorrhizal inocula may be an important factor affecting the dynamics of plant communities. We investigated the persistence and diversity of ericoid mycorrhizal fungi in the soil of a mature Quercus ilex forest where ericaceous hosts were absent. Erica arborea was used as a bait plant and results were compared to soil samples from experimental plots where cuttings had allowed reappearance of this ericaceous species. Fungal endophytes were isolated and tested in mycorrhiza resynthesis trials. Sterile mycorrhizal endophytes were assigned to morphotypes whose consistency was confirmed by ITS-RFLP. The ITS region of a representative of each morphotype was sequenced. BLAST searches and Neighbour-Joining analysis indicated taxonomic affinities with different classes within Ascomycota. Our results indicate that ericoid mycorrhizal fungi persist and maintain mycorrhizal ability in habitats lacking the ericaceous host. Their persistence could favour the establishment of E. arborea seedlings in pure Q. ilex forests after disturbance phenomena.

Diversity of sterile root-associated fungi of two Mediterranean plants.

• The diversity of dark sterile mycelia (DSM) associated with the roots of neighboring healthy ectomycorrhizal Pinus halepensis and endomycorrhizal Rosmarinus officinalis plants in a Mediterranean ecosystem in Italy was investigated to assess taxonomic affinities of these poorly known root endophytes. • More than 260 fungal isolates were obtained and ascribed to distinct morphotypes based on their macro- and microscopic features. Polymerase chain reaction-restriction fragment length polymorphism and sequence analyses of the internal transcribed spacers (ITS1-5.8S-ITS2) and 18S rDNA regions were carried out for representatives of the morphotypes obtained from both hosts over an 11-yr period. • Molecular evidence matched morphological group circumscription. Recognition of systematic affinities was possible with varying degrees of resolution for the different morphotypes. Morph 2 was closely related to Rhizopycnis vagum (within Dothideomycetidae), Morph 1 to Diaporthe / Phomopsis (within Sordariomycetidae), whereas Morphs 3a, 3b, 3c and 3d could only be given taxonomic placement at a higher level (Dothideomycetidae and Chaetothyriomycetidae). • This peculiar systematic spectrum suggests that actual DSM diversity in nature is still largely underestimated. Morphophysiological convergence among morphotypes, and ecological traits possibly involved in interactions with plant hosts are discussed.

Nuclear ribosomal sequence analysis of Oidiodendron: towards a redefinition of ecologically relevant species.

• Nuclear ribosomal sequence analysis was performed to investigate delimitation of common Oidiodendron species comprising endomycorrhizal symbionts and close associates of ectomycorrhizal plants. • Neighbour-joining, maximum likelihood and parsimony analyses were used to compare 35 ribosomal DNA (internal transcribed spacer (ITS) and 5.8S) sequences (including sequences available in databases) from 15 putative species. • Oidiodendron citrinum formed a monophyletic group nested within O. maius, whereas O. tenuissimum and O. griseum did not appear either as distinct groups or as a single complex. Pairwise nucleotide divergence values between O. citrinum and O. maius were very low and comparable to intraspecific values obtained for both species; values for O. griseum and O. tenuissimum, although higher, overlapped those observed at the intraspecific level for the two species. • Molecular data indicate that O. maius and O. citrinum, which were described as distinct, though related species, could be moved to a subspecific level; however, the delimitation of O. griseum and O. tenuissimum is still open to question. Taxonomic rank assignment to groups determined from sequence data analysis is discussed.