Ana María de Miguel

Truffles in the genus Tuber (Pezizales) are among the few ectomycorrhizal taxa successfully cultivated worldwide. Australia has recently become one of the top producers of Tuber melanosporum , a high-valued black truffle native to Europe. Truffle co-introductions in the Southern Hemisphere with their Northern Hemisphere plant symbionts are hypothesized to benefit from reduced ectomycorrhizal competition and natural enemies. In this study, we tested whether T. melanosporum in Australia experiences competition release by sampling soils and truffles across France, Spain, Italy, and Australia. Fungal and prokaryotic communities in truffle plantations were assessed in native (European) and non-native (Australian) habitats through ITS and 16S rDNA amplicon sequencing from soil and truffles. Community composition was primarily structured by site of origin and secondarily by presence of brûlé, vegetation-free area induced by truffle production of plant-growth inhibiting compounds, with significant interactions indicating site-dependent brûlé effects. European soils showed higher fungal richness outside the brûlé, with higher evenness overall and for ectomycorrhizal fungi only outside brûlé. T. melanosporum showed higher abundance in Australia, with significant differences restricted to outside the brûlé. Overall, ectomycorrhizal fungi in European soils had more than four times the taxa and higher diversity compared to Australian soils. Among the main competitors, Tomentella , Inocybe , and Trichophaea co-dominated in Europe, versus Scleroderma , Hebeloma , and Tarzetta in Australia. Despite differences in soil microbiomes, bacterial communities within T. melanosporum truffle ascocarps were strikingly similar across sites and continents and were dominated by Bradyrhizobium . Despite high site-level variation, our results support the competition release hypothesis, with reduced enemies benefiting T. melanosporum colonization outside the brûlé in Australia. IMPORTANCE: This study provides the first cross-hemisphere analysis of the truffle microbiome, comparing native and non-native soils and truffles from Europe and Australia. We demonstrate that the remarkable success of Tuber melanosporum cultivation in Australia is compatible with ecological release from competitors, which favors its development outside the brûlé. At the same time, we reveal striking cross-hemispheric similarities in truffle-associated bacterial communities, consistently dominated by Bradyrhizobium . These findings highlight both the novelty and transcontinental relevance of our work, offering new perspectives on fungal ecology and truffle cultivation.

Truffles are edible hypogeous ascomycetes highly appreciated worldwide, especially the black truffle (Tuber melanosporum Vittad.). In recent decades, the cultivation of the black truffle has expanded across the Mediterranean climate regions in and outside its native range. Members of the Thelephoraceae (Thelephorales, Agaricomycetes, Basidiomycota) are commonly found in truffle plantations, but their co-occurrence with Tuber species and other members of the fungal community has been scarcely reported. Thelephoraceae is one of the most represented families of the ectomycorrhizal fungal community in boreal and Mediterranean forests. To reveal the diversity of these fungi in T. melanosporum-cultivated plantations, ten orchards located in the Navarra region (Northern Spain) were surveyed for 2 years. Morphological and molecular approaches were used to detect and identify the Thelephoraceae ectomycorrhizas present in those plantations. Ten different mycorrhizal types were detected and described. Four of them were morphologically identified as Tomentella galzinii, Quercirhiza cumulosa, Q. squamosa, and T39 Thelephoraceae type. Molecular analyses revealed 4–6 operational taxonomic units (OTUs), depending on the nucleotide database used, but similarities remained under 95 % and no clear species assignments could be done. The results confirm the diversity and abundance of this fungal family in the ectomycorrhizal community of black truffle plantations, generally established in Mediterranean areas. The occurrence and relative abundance of Thelephoraceae ectomycorrhizas is discussed in relation to their possible influence on truffle production.

Aim of study: The program "Typology of truffle stations in the Pyrenean Regions" aimed to define the ecological conditions and culture practices that favor Tuber melanosporum growth and fruiting in this area.Area of study: Navarra, Catalonia, Midi-Pyrénées and Languedoc-Roussillon.Material and methods: The program was based on the survey of 212 wild and cultivated truffle beds of evergreen oaks (Quercus ilex). The data collected in the field consisted of photographs, samples of soil, roots and mycorrhizae, and information on cultural practices followed by truffle growers.Main results: (i) truffle soils are alkaline, from neutral, dolomitic, to moderately or very calcareous soils; (ii) truffle soils are light, well-structured and stable to water immersion; (iii) mycelium that colonizes roots survives in suboptimal conditions, but it does not necessarily bear ascocarps. Finally our results suggest that T. melanosporum is a relatively ubiquitous fungus able to grow, or at least to persist, in a wide range of physical and chemical soil conditions. We propose a probabilistic model of the environment favorable for fruiting, built around a two-dimensional graph with an axis for the chemical conditions, like soil alkalinity, and another axis for the physical conditions, like soil structure. Research highlights: Soil alkalinity and structure allow to built a convenient representation of the ecological capacity of a place to be good T. melanosporum habitat, and thus of the probability for truffle growers to harvest truffles according to the environmental properties of their truffle orchards.Keywords: dolomite; limestone; mycorrhizae; Quercus ilex; field survey; Tuber melanosporum.

Aims of the study: The goals of this paper are to provide preliminary data on the composition of the mite community in truffle-producing soils (both wild and plantations); and to elucidate those species which may interact with the black truffle life cycle.Area of study: The study was carried out in two black truffle productive zones in Navarra (Spain), in four different plantations and five wild production areas.Material and Methods: Fauna was extracted using Berlese Tullgren funnels. Animals were separated into taxonomic groups, and mites were identified. To analyse the composition and community structure of the different habitats, parameters such as abundance, species richness, and Shanon Weiner diversity index (H’) were calculated.Main results: A total of 305 mites were recognized, belonging to 58 species representing the three major taxonomic groups (Oribatida, Prostigmata, Mesostigmata).Research highlights: The results show a possible trend towards wild areas having greater diversity and species richness than plantations. Furthermore, community analysis shows differences in species compositions among different study areas, and oribatid mites always exhibit the highest relative abundance and species richness.Keywords: Acari; Tuber melanosporum; Oribatida; Mesostigmata; Prostigmata; truffle orchards.

Owners of black truffle (Tuber melanosporum) plantations are concerned about the persistence of its mycorrhizas and mycelium in the soil, especially until the appearance of the “truffle burn” areas and the triggering of sporocarp production, at least 5–7 years after planting truffle-inoculated seedlings. During this period, the farmer does not know whether his management is promoting black truffle development. To study the presence and abundance of T. melanosporum ectomycorrhizas in plantations, two sampling methods, direct sampling of root tips and soil core collection, are compared by analyzing 48 evergreen oak trees (Quercus ilex) inoculated with truffle. Those trees are grouped by age (9 years old) and presence or absence of truffle production. T. melanosporum was present in 46 out of the 48 studied trees, and its ectomycorrhizas appeared in 65 % of the ectomycorrhizal tips. Its abundance is significantly higher with productive trees and young trees. Direct sampling of root tips and soil core collection were equally effective in detecting this species, although soil core collection proved a better method to also evaluate ectomycorrhizal fungal diversity. To detect the presence of T. melanosporum in a given plantation, three samples suffice, with a single sample per random tree. Although the presence of mycorrhizas is not a sure sign of the future success of a black truffle plantation, its absence influences managers as to whether to continue culturing truffles in a plantation.

Since the first truffle plantations were established in France, Italy and other parts in the world, many studies have been carried out to improve their productivity and sustainability. Success of plantations is clearly related to the mycorrhizal status of the host trees over the years, from inoculated seedlings to truffle-producing trees. The experience gained in monitoring the ectomycorrhizal fungus status in cultivated truffle grounds has allowed us to develop an extensive catalogue of the ectomycorrhizal fungi present in truffle plantations. Herein, we summarize fungal community data from 85 references that represent different truffle studies in natural habitats and plantations. Approximately 25 % of the ectomycorrhizae reported in the 85 references are common to most of the studies. In general, more fungal species are detected in productive plantations than in the non-productive ones. Truffle plantations display a diverse ectomycorrhizal fungal community, in which species of the genus Tuber are well represented. Tuber rufum and some members of Boletales are typically restricted to productive truffle plots. On the other hand, Hebeloma, Laccaria and Russula species are mostly associated with unproductive plots. Ectomycorrhizae belonging to Thelephoraceae are frequently found in mature truffle orchards but do not seem to affect sporocarp production. Several biotic and abiotic factors affect the ectomycorrhizal fungus communities associated with truffle orchards. Among them are plantation age, host species and its growth, the surrounding environment (particularly the presence of other ectomycorrhizal hosts), and plantation management. Understanding the ectomycorrhizal fungal communities inhabiting different plantations may give us clues about the dynamics of the targeted truffles and the possibility of identifying mycorrhizal fungal species that are good indicators of successful truffle plantations.