Tuber melanosporum is an ectomycorrhizal (ECM) fungus from Mediterranean transitory ecosystems where ECM trees start to dominate among arbuscular-mycorrhizal (AM) shrubs and herbs (companion plants). Its presence entails the development of 'brûlés', where 2 vegetation is scarce for unknown reasons. Current T. melanosporum production comes from plantations where management often suppresses the understory vegetation, although empirical knowledge advocates a positive role of some companion plants in truffle production. This study aimed at (i) experimentally testing the reciprocal interaction between T. melanosporum and companion plants and (ii) examining T. melanosporum-mediated soil feedback involved in the dynamics of truffle ground vegetation. Methods A three-year experiment was set up with Quercus ilex associated with T. melanosporum (or not, as control), grown in association (or not, as control) with a companion plant. Six companion plant species were chosen based on different empirical criteria including those indicated by local truffle growers' knowledge. A trait-based approach was applied to plants and associated fungi (abundance of T. melanosporum and AM fungi mycelium). Results-Conclusion Companion plants promoted the development of truffle mycelium. In the presence of T. melanosporum, companion plant growth and nutrition and AM fungi abundance decreased, while the nutrition status of its host increased. The truffle inhibited germination of weed seeds. These results highlight the role of T. melanosporum in mediating plant-plant interactions, possible mechanisms underlying brûlé formation and a potential successional role for T. melanosporum.

The nomenclatural type material of Rhizophagus intraradices (basionym Glomus intraradices) was originally described from a trap pot culture established with root fragments, subcultures of which later became registered in the INVAM culture collection as FL 208. Subcultures of FL 208 (designated as strain ATT 4) and a new strain, independently isolated from the type location (ATT 1102), were established as both pot cultures with soil-like substrate and in vitro root organ culture. Long-term sampling of these cultures shows spores of the species to have considerable morphological plasticity, not described in the original description. Size, shape and other features of the spores were much more variable than indicated in the protologue. Phylogenetic analyses confirmed earlier published evidence that sequences from all R. intraradices cultures formed a monophyletic clade, well separated from, and not representing a sister clade to, R. irregularis. Moreover, new phylogenetic analyses show that Rhizoglomus venetianum and R. irregularis are synonymous. The morphological characters used to separate these species exemplify the difficulties in species recognition due to the high phenotypic plasticity in the genus Rhizophagus. Rhizophagus intraradices is morphologically re-described, an epitype is designated from a single-spore isolate derived from ATT 4, and R. venetianum is synonymised with R. irregularis.

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