Ecological niche construction by ectomycorrhizal Tuber species (truffles) was described in alkaline soils in Mediterranean ecosystems but its variability depending on fungal species and soil environment is poorly known. The objective was to determine whether Tuber species construct niches in environments with low carbonate content or under acidic conditions, and how this niche construction can be observed at both the rhizosphere and brûlé scales. A total of 213 soil samples associated with four Tuber species were analyzed at rhizosphere and brûlé/patch scales across seven geographical regions, ranging from highly alkaline to moderately and highly acidic soils. All 4 Tuber species raised soil pH when comparing soils inside and outside their brûlés/patches: T. oregonense in very acidic soils, T. melanosporum and T. brumale in neutral to slightly alkaline soils, and T. aestivum in alkaline soils. Concomitantly, T. melanosporum and T. brumale increased exchangeable Ca2+, thereby further alkalising slightly calcareous soils. Tuber melanosporum increased Ca2+ by decalcifying highly calcareous soils. At the rhizosphere scale, the mycelium of T. aestivum was negatively correlated with soil pH in decalcified and neutral soils. The mycelium of T. melanosporum was positively correlated with exchangeable Ca2+/Mg2+ and negatively with P and exchangeable Mg2+ availability in alkaline soils, thereby modifying soil fertility in the host plant rhizospheres. We infer that Tuber species control the abundance and chemical forms of soil Ca by regulating soil pH (through changes in the fungal-plant excretions of low-molecular-weight organic anions and their complex effect on soil pH, inorganic components and microorganisms), a mechanism likely shared by other ectomycorrhizal fungi and one that could affect the nutrition of host plants.

The ectomycorrhizal fungi Tuber melanosporum Vittad. and Tuber aestivum Vittad. produce highly valuable truffles, but little is known about the soil fungal communities associated with these truffle species in places where they co-occur. Here, we compared soil fungal communities present in wild and planted truffle sites, in which T. melanosporum and T. aestivum coexist, in Mediterranean and temperate regions over three sampling seasons spanning from 2018 to 2019. We showed that soil fungal community composition and ectomycorrhizal species composition are driven by habitat type rather than climate regions. Also, we observed the influence of soil pH, organic matter content and C:N ratio structuring total and ectomycorrhizal fungal assemblages. Soil fungal communities in wild sites revealed more compositional variability than those of plantations. Greater soil fungal diversity was found in temperate compared to Mediterranean sites when considering all fungal guilds. Ectomycorrhizal diversity was significantly higher in wild sites compared to plantations. Greater mould abundance at wild sites than those on plantation was observed while tree species and seasonal effects were not significant predictors in fungal community structure. Our results suggested a strong influence of both ecosystem age and management on the fungal taxa composition in truffle habitats.

Black truffle plantations are established on the basis that Tuber melanosporum Vittad. spreads from artificially inoculated trees. Although truffle cultivation has progressed tremendously over the past 30 years, the ecological processes underlying T. melanosporum mycelium expansion and its interactions with the rest of the fungal community over time are not completely understood. Controversy exists on how mating type distribution evolves with time and its incidence on truffle production. We studied the soil fungal community and mating type distribution in plantations before truffle production (3, 5 and 7 years and after plantation establishment) and during the production period (10, 14 and 20 years) at three distances from the tree stem: 40, 100 and 200 cm. We found that T. melanosporum developed steadily over the years as extraradical mycelium, first at the nearest part of the tree and later up to 200 cm. T. melanosporum development was not correlated with changes in other ectomycorrhizal fungi and was negatively correlated with lower relative abundance of arbuscular mycorrhizal fungi and of non-root associated guilds such as moulds, yeasts and plant pathogens. Mating type frequency did not change across years. Twenty years after establishment no signs of replacement of T. melanosporum by other fungi nor biases in mating type abundance were observed in soil mycelia, indicating that T. melanosporum can colonize and dominate the surrounding soil in mature Quercus ilex L. plantations.

Climate change has been described as the main threat for the cultivation and growth of truffles, but hydroclimate variability and model uncertainty challenge regional projections and adaptation strategies of the emerging sector. Here, we conduct a literature review to define the main Périgord truffle growing regions around the world and use 20 global climate models to assess the impact of future trends and extremes in temperature, precipitation and soil moisture on truffle production rates and price levels in all cultivation regions in the Americas, Europe, South Africa, and Australasia. Climate model simulations project 2.3 million km2 of suitable land for truffle growth will experience 50% faster aridification than the rests of the global land surface, with significantly more heat waves between 2070 and 2099 CE. Overall, truffle production rates will decrease by ∼15%, while associated price levels will increase by ∼36%. At the same time, a predicted increase in summer precipitation and less intense warming over Australasia will likely alleviate water scarcity and support higher yields of more affordable truffles. Our findings are relevant for truffle farmers and businesses to adapt their irrigation systems and management strategies to future climate change.

Trained dogs can detect many biochemical traces, from the most hostile, such as COVID-19, to the most expensive, such as truffles. However, it is still unclear how the interplay of genetic disposition, education, experience, personality, and environmental conditions influences the performance of dogs. Here, we combine published evidence with the knowledge of truffle hunters to assess direct and indirect factors that affect the hunting performance of truffle dogs. Since the transport of truffle aroma into the canine nasal cavity is most puzzling, we propose 5 experiments to further investigate the role of weather conditions, soil parameters, and bacterial composition on the dispersal of truffle volatiles perceived by trained dogs. We also suggest exploring whether the application of multiple dogs increases the success of truffle hunting. Moreover, we argue that interdisciplinary research on dog behavior and performance, including insights from veterinary science and comparative psychology as well as the experience of truffle hunters and farmers, is needed to improve the quantity and quality of truffle harvests.

Aim of study: Wild mushrooms are among the most widespread non-wood forest products in the Mediterranean region contributing to the rural economies. However, the wild mushroom sector still faces problems along its supply chain that can compromise its future in a scenario of increasing demand. The aim of this study was to analyse the current epigeous wild mushroom sector. Area of study: Representative countries of the Mediterranean region: Spain, France, Italy, Croatia and Greece. Materials and methods: The analysis was carried out through a structured Delphi survey conducted in two rounds, with a questionnaire divided into four groups: 1) supply chain description, 2) sectorial SWOT analysis, 3) future challenges and 4) sectorial resilience increase. The Delphi survey started with the selection of an expert panel that included 14 representatives of the wild mushroom supply chain such as forest owners, mushroom pickers, processing industry and consumers. Main results: The results obtained from the expert panel confirmed the complexity of the wild mushroom supply chain with the following sectorial challenges: i) Traceability and sustainability is fundamental for the final consumer, ii) Sectorial administration should be more coordinated, iii) Mushroom picking should be regulated, as the grey market will decrease. Research highlights: The study identified the most important actions that will strengthen the links among sectorial actors and interconnect gastronomy with mushrooms sector. The creation of a common EU list of commercial mushroom species and the development of a taxation system together with the product traceability were also addressed.

Aim of study: We aimed to i) evaluate the effects of mulching on Tuber melanosporum mycelium biomass and seedling growth (i.e. root collar diameter and seedling height) and ii) unravel the relationship between growth in root collar diameter and mycelium abundance, in a T. melanosporum plantation. Area of study: The experimental plantation is located in the Pre-Pyrenees mountains in Catalonia, Spain. Material and methods: The experimental plantation was established in 2010 using one-year-old T. melanosporum inoculated Quercus ilex seedlings. Double-layered mulch materials were placed around the seedlings. The mulch materials were removed from randomly selected seedlings in 2015 and 2018. Soil samples were collected in 2018 at 40 and 80 cm distances from seedlings that had mulching during five and eight years, and T. melanosporum mycelium biomass was estimated by quantitative Polymerase Chain Reaction (qPCR). Seedling root collar diameter and height were measured simultaneously when mulch materials were removed. Main results: Mulch removal time did not have significant effects on T. melanosporum mycelium biomass or seedling growth. However, mycelium biomass at 40 cm distance tended to be higher on seedlings after eight-year mulching with 0.9 mg/g soil whereas mycelium biomass was 0.4 mg/g soil after five-year mulching. A positive relationship between mycelium biomass and seedling root collar diameter was also found. Research highlights: Mulching seems to have a positive effect on truffle mycelium biomass, with nearly two times higher quantity of mycelium after eight-years compared with five-years mulching usage. Seedling root collar diameter is a good indicator of mycelium expansion in the plantation. Keywords: Black truffle; Quercus ilex; mulching; tree growth; truffle cultivation.

Background: The objective of this study was to analyze the current situation of the truffle sector in the main producing countries of the Mediterranean area. Additionally, we identified the challenges for the future and the priority actions to develop the truffle sector in the region. Methods: We used a Delphi process approach, and we selected a total of 17 expert panelists in different positions within the supply chain of the target countries (Spain, France, Italy, Croatia, and Greece). Results: The results obtained allowed us to have a complete description of the current truffle supply chain. We confirmed an evolution of the sector due to the cultivation success of several Tuber species. The maturity of the sector has produced shifts in the roles that form the traditional truffle supply chain operators. We confirmed the trend of a decrease of collectors that hunt truffles in the wild and sell to small travelling buyers, whilst truffle hunters that collect for farmers and specialty wholesalers are emerging. However, a trend of truffle price decrease in the last few years has alerted the sector. Conclusions: As production increases due to truffle cultivation, it will be necessary to promote truffle consumption. We identified actions to develop the truffle sector: (a) strengthen the link between truffles, tourism, and gastronomy; (b) increase the effort at European level for the recognition of truffle production, helping to develop truffle culture and marketing; (c) increase the awareness and consumption of truffles among consumers; and (d) develop tourism workshops for truffle farmers.

Black truffles are a highly valued non-wood forest product. The success of truffle plantations is arousing the interest to establish orchards within forest settings. One main concern is that the forest may act as a source of ectomycorrhizal fungi that could displace Tuber melanosporum in plantations and impair truffle production. We studied the effects of host tree distance to the surrounding forest on T. melanosporum development and on the root-associated fungal community. Our research was carried out in a 5-year old holm oak (Quercus ilex) plantation established in an abandoned pasture surrounded by a Q. ilex forest in the Pyrenees. The spatial distribution of different fungal guilds as well as of T. melanosporum mycelium quantity and mating types frequency was correlated with the distance to the forest and the diameter of the trees. We found a higher relative abundance of non-T. melanosporum EcM fungi associated with the trees closer to the forest. Larger root collar diameter trees had greater biomass of T. melanosporum mycelium and displayed fungal community compositions less affected by the distance to the forest. No associations between the biomass of T. melanosporum mycelium in the soil and the distance to the forest or the abundance of non-T. melanosporum EcM fungi were observed. Our results indicate that T. melanosporum inoculated oaks planted in areas surrounded by forests may be colonised by other ectomycorrhizal species, and develop a distinct microbial community from those usually established in agricultural lands. Further investigations should be carried out to determine whether a different fungal community may affect truffle production in the future, but to date, truffle mycelium does not seem to be impaired.

Research Highlights: Mycorrhizal helper bacteria (MHB) promote mycorrhization processes and are commonly found in the mycorrhizosphere of fungi, such as the edible hypogeous fungusTuber melanosporumVittad.Background and Objectives: The effectiveness of MHB in promoting the mycorrhization process and the root development of Portuguese oak (Quercus fagineaLam.) seedlings destined for truffle plantations has not been determined. The main aim of this study was to shed light on the effect of bacterial inoculation on fungal root tip colonization and seedling root traits.Material and methods: We performed a co-inoculation trial using three bacteria naturally present in theT. melanosporumniche (i.e.,Pseudomonas fluorescens,Pseudomonas putida, andBacillus amyloliquefaciens) and two different bacterial inoculation times (one month and nine months after fungal inoculation) under glasshouse conditions.Results: OnlyP. fluorescenshad a significant mycorrhizal promoter effect, increasing the truffle inoculation rates of root tips by more than 10% compared with seedlings that received non-bacterial inoculation treatments. Simultaneously, the co-inoculation ofP. fluorescenswithT. melanosporumimproved seedling root growth parameters compared with those of seedlings that received non-bacterial inoculation treatments. The different bacterial inoculation times and applications of uninoculated bacterial growth media did not affect the root traits analyzed or the root mycorrhization rates.Conclusions: These results suggest thatP. fluorescensbacteria have a potential commercial application as a treatment for truffle-inoculated seedlings to improve both seedling quality and mycorrhizal colonization under nursery conditions.

Climate change affects the distribution of many species, including Burgundy and Périgord truffles in central and southern Europe, respectively. The cultivation potential of these high-prized cash crops under future warming, however, remains highly uncertain. Here we perform a literature review to define the ecological requirements for the growth of both truffle species. This information is used to develop niche models, and to estimate their cultivation potential in the Czech Republic under current (2020) and future (2050) climate conditions. The Burgundy truffle is already highly suitable for cultivation on ~ 14% of agricultural land in the Czech Republic (8486 km2), whereas only ~ 8% of the warmest part of southern Moravia are currently characterised by a low suitability for Périgord truffles (6418 km2). Though rising temperatures under RCP8.5 will reduce the highly suitable cultivation areas by 7%, the 250 km2 (3%) expansion under low-emission scenarios will stimulate Burgundy truffles to benefit from future warming. Doubling the moderate and expanding the highly suitable land by 352 km2 in 2050, the overall cultivation potential for Périgord truffles will rise substantially. Our findings suggest that Burgundy and Périgord truffles could become important high-value crops for many regions in central Europe with alkaline soils. Although associated with uncertainty, long-term investments in truffle cultivation could generate a wide range of ecological and economic benefits.

The unprecedented price inflation of Black truffles, recently exceeding 5000 Euro kg(-1) (in Zurich), is a combined result of increasing global demands and decreasing Mediterranean harvests. Since the effects of long-term irrigation and climate variation on symbiotic fungus-host interaction and the development of belowground microbes are poorly understood, the establishment and maintenance of truffle plantations remains a risky venture. Using 49 years of continuous harvest and climate data from Spain, France and Italy, we demonstrate how truffle production rates, between November and March, significantly rely on previous June-August precipitation totals, whereas too much autumnal rainfall affects the subsequent winter harvest negatively. Despite a complex climate-host-fungus relationship, our findings show that southern European truffle yields can be predicted at highest probability (r = 0.78, t-stat = 5.645, prob = 0.000 01). Moreover, we demonstrate the reliability of national truffle inventories since 1970, and question the timing and dose of many of the currently operating irrigation systems. Finally, our results suggest that Black truffle mycorrhizal colonization of host fine roots, the sexualisation of mycelium, and the formation of peridium are strongly controlled by natural summer rainfall. Recognising the drought-vulnerability of southern Europe's rapidly growing truffle sector, we encourage a stronger liaison between farmers, politicians and scientists to maintain ecological and economic sustainability under predicted climate change in the Mediterranean basin.

Whenever a new invasive forest pathogen appears, resources are put into developing countermeasures such as breeding for resistance in the affected host species and/or by developing fungicide/biocontrol treatments. In most cases, little effort is placed into analysing the likelihood of those measures being implemented. Studying the reasoning behind management reactions of forest managers whose forests had been attacked by invasive pathogens can improve implementation of measures in case of future invasions. We used grounded theory to model forest owners' reactions against chestnut blight caused by the invasive pathogen Cryphonectria parasitica. We focussed on understanding what drove some managers to keep managing chestnut forests and applying biological control, and what made others abandon or even substitute chestnut by exotics. We found that the availability of a market for chestnut products, and not the disease was the main reason for discontinuing chestnut management. The will to continue managing chestnuts was four times higher amongst managers of chestnut stands for nut production (valuable crop), than amongst managers of coppice stands producing small diameter stems, currently without a market. Requesting application of biological control against chestnut blight was four times more likely amongst forest managers obtaining monetary benefits from their land (benefits used as profit or re-investment) than those not obtaining monetary benefits or currently losing money with their land. Substitution with exotic conifers was associated with forest managers that had learned management from family and leaders of opinion, and that have either themselves or previous owners of the land planted exotics beforehand. Abandonment was associated with self-taught managers valuing non-monetary aspects of forests and having moral reasons against exotics. Our research highlights the importance of considering the socioeconomic context around the affected tree species when developing measures against invasive forest pathogens, and raises concerns about the continuity of tree species affected by invasive pathogens with little or no commercial value. (C) 2016 Elsevier B.V. All rights reserved.

Tuber melanosporum belongs to the genus Tuber that only includes mycorrhizal fungi living and fruiting underground within the soil environment. T. melanosporum prefers sites in ridges or slopes, where water does not accumulate, and fractured parent materials where water can drain well. Rocky soils with crumb or subangular blocky structure, whose aggregates are stable to fast water immersion, are preferable for truffle cultivation, mostly when their texture is balanced and their clay content moderate. Tuber fungi thrive in alkaline soils with their exchange complex saturated by calcium or magnesium and high in well-mineralised organic matter. These soil conditions are all common in the landscape, but they seldom occur all at the same site. This is what makes natural truffle habitat scarce and disperse. Yet several of these soil characteristics can be modified and many farmlands can become excellent truffle orchards with the adequate soil management practices. These include liming, tilling or adding rock fragments and well-decomposed organic matter in soil.

Cryphonectria parasitica (Murrill.) Barr is a necrotrophic fungus that affects European chestnut populations. In Catalonia (NE Spain), this fungus is widely spread affecting chestnut stands. In addition to vegetative compatibility (VC) types of the fungus, knowledge of the Cryphonectria hypovirus (CHV) occurrence is important to implement a biocontrol programme. We confirmed the presence of hypoviruses in several chestnut subpopulations of Catalonia, and we determined the VC types of CHV-infected isolates. We also studied the nucleotide sequences of these hypoviruses from a variable region located in the hypovirus ORF-A. Our results show a low occurrence of hypoviruses throughout C.parasitica populations in Catalonia, except for a few localized stands. From 312 sampled cankers, we obtained 179 white, pale orange or rickety isolates. In 35 of them, we detected CHV-1. Infected isolates belonged to 5 of the 7 sampled subpopulations. We found 12 CHV-1 haplotypes, based on the nucleotide sequence analysis. Most of the hypoviruses have the same nucleotide sequence or show high homology at nucleotide level with isolates previously included in CHV-1 subtype-I. However, we found that 3 haplotypes share at least 97% of their ORF-A nucleotide sequence with CHV-1 subtype-E. Phylogenetic analysis grouped these 3 isolates in a different cluster than the other hypoviruses. These results suggest that multiple introductions of CHV-1 have occurred recently in Catalonia. Dominant VC types of hypovirus-infected isolates are EU-1, EU-2 and EU-5, which are similar to those previously reported in this region.

The Perigord black truffle is an exclusive culinary delicacy, but its Mediterranean harvests have declined, despite cultivation efforts since the 1970s. The role of long-term irrigation, symbiotic fungus-host interaction, and microbial belowground progression remain poorly understood, because generally too short experimental settings miss the necessary degree of real world complexity and reliable information from truffle orchards is limited. Here, we conduct the first dendrochronologicai and wood anatomical assessment of 295 holm oaks, which have been growing under different irrigation intensities in the world's largest truffle orchard in Spain. The relationships between different climatic variables (monthly temperature means and precipitation totals) and dendro-parameters (ring width, vessel count and vessel size) of the oak hosts are utilized to disentangle direct and indirect drivers of truffle fruit body production. Irrigation at medium - instead of high - intensity is most beneficial for oak growth. Non-irrigated trees reveal overall lower stem increments. Warmer temperatures from February to April and wetter conditions from May to July enhance host vitality and possibly also its interplay with fungi symbionts via increased fine root production and mycorrhizal colonization. Adequately irrigated Mediterranean orchards may counteract some of the drought-induced natural truffle decline, and help stabilizing rural tourism, regional agriculture and global markets. (C) 2014 Elsevier B.V. All rights reserved.

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.