Tuber Magnatum Research Articles

Site characteristics of Tuber magnatum in Greece

Day after day it is being demonstrated that Greece hides a buried treasure in its forests. The wild black truffles <em>Tuber aestivum, T. uncinatum, T. brumale </em>and <em>T. melanosporum </em>and the white truffle <em>T. borchii </em>and recently <em>T. magnatum </em>are picked in a variety of forest ecosystems all over the country. The information which has been collected has initiated a national programme on truffle cultivation which, so far, has immense appeal, especially among young farmers. The discovery of carpophores of <em>T. magnatum</em>, the most valued white truffle in the market, triggered the interest in studying the site characteristics, botanical and pedological, in order to help farmers to cultivate the species in similar sites. All carpophores were found under hornbeam (<em>Carpinus orientalis</em>) along the banks of a creek on alluvial sediment. Soil analyses of four soil samples from truffle nests showed a narrow range of values of pH in water (7.57–7.78) and 1N KCL (6.94–7.07) and a similar granulometric soil texture.

Effects of soil tillage on Tuber magnatum development in natural truffières

Tuber magnatum Pico, the Italian white truffle, commands the highest prices of any truffle. Despite its commercial value, it is the only edible European truffle which has not yet been successfully cultivated. Because of this, it is essential to safeguard natural truffières and to identify cultural practices to maximize their productivity. Soil tillage is successfully and extensively used in black truffle cultivation to enhance productivity, but its effects are not known on the development of T. magnatum. A recently developed real-time PCR assay was applied to evaluate the effects of tillage (10-15 cm depth) on T. magnatum mycelium in two different natural truffle grounds located in Tuscany and Emilia-Romagna. Tillage effects on bulk density, ectomycorrhizal fungal communities, and ascoma production were also assessed. Tilling significantly increased the quantity of T. magnatum mycelium which seemed to be related to an increase in soil porosity by up to 34%, and the diversity of ectomycorrhizal fungal communities. On the contrary, no significant effects were found on ascoma production. The results highlight that real-time PCR is the most reliable method for evaluating the effects of cultural practices on the development of T. magnatum in soil avoiding long-term studies on fruiting body production.

Actinobacteria may influence white truffle (Tuber magnatum Pico) nutrition, ascocarp degradation and interactions with other soil fungi

Abstract To test the hypothesis that truffle-associated bacteria may improve truffle nutrition, we isolated bacteria from white truffle ascocarps and tested Actinobacteria for their ability to solubilise phosphate and iron, nutrients that have limited availability in white truffle grounds. Two isolates with sequence similarities to Curtobacterium flaccumfaciens and Rhodococcus sp. were characterized in detail. Both solubilised Ca 3 (PO 4 ) 2 in a way that was dependent on the nitrogen and carbon sources present. Neither strain broke down phytate, but both produced chelating compounds, performed ammonification, and broke down β-glucan. Additionally, C. flaccumfaciens decomposed chitin, pectin, lipids and proteins, while Rhodococcus sp. exhibited urease activity. Three potentially fungicolous fungi were isolated from diseased white truffle ascocarps and bioassayed against the isolated Actinobacteria. The Rhodococcus isolate inhibited Verticillium leptobactrum , neither bacterium affected Clonostachys rosea , while both isolates promoted growth of Trichoderma sp. The results suggest that Actinobacteria might be involved in improving truffle nutrition, ascocarp degradation and establishing relationships with other soil fungi.

Composition of commercial truffle flavored oils with GC–MS analysis and discrimination with an electronic nose

Truffles are among the most expensive foods and their quality depends on their unique aroma, composed of complex mixtures of lipophilic volatile organic compounds (VOCs). There are many foods flavored with truffle, and oils are particularly common. Using DHS–GC–MS and an electronic nose (MOS), 18 samples of olive oil flavored with white and black truffles from the Italian market were subjected to a blind analysis. Qualitative and quantitative analysis with DHS–GC–MS detected the presence of 63 VOCs, 32 of which can be attributed to olive oil, also defective, and 19 to truffles, while 12 foreign compounds are of dubious origin (synthesis and/or demolition). The data obtained with the electronic nose (MOS), processed statistically, was able to discriminate the aromas coincident with the three species of truffle declared on the label (the white truffle Tuber magnatum and the black truffles Tuber melanosporum and Tuber aestivum), demonstrating the potential and reliability of this technique, confirming the established malpractice of the use of bismethyl(dithio)methane in black truffles flavorings.

Proteins from Tuber magnatum Pico fruiting bodies naturally grown in different areas of Italy

BackgroundA number of Tuber species are ecologically important. The fruiting bodies of some of these also have value as a cooking ingredient due to the fact that they possess exceptional flavor and aromatic properties. In particular, T. magnatum fruiting bodies (commonly known as truffles), are greatly appreciated by consumers. These grow naturally in some parts of Italy. However, the quality of these fruiting bodies varies significantly depending on the area of origin due to differences in environmental growth conditions. It is therefore useful to be able to characterize them. A suitable method to reach this goal is to identify proteins which occur in the fruiting bodies that are specific to each area of origin. In this work protein profiles are described for samples coming from different areas and collected in two successive years. To our knowledge this is the first time that proteins of T. magnatum have been thoroughly examined.ResultsUsing two dimensional electrophoresis, reproducible quantitative differences in the protein patterns (total 600 spots) of samples from different parts of Italy (accession areas) were revealed by bioinformatic analysis. 60 spots were chosen for further analysis, out of which 17 could probably be used to distinguish a sample grown in one area from a sample grown in another area. Mass spectrometry (MS) protein analysis of these seventeen spots allowed the identification of 17 proteins of T. magnatum.ConclusionsThe results indicate that proteomic analysis is a suitable method for characterizing those differences occurring in samples and induced by the different environmental conditions present in the various Italian areas where T. magnatum can grow. The positive protein identification by MS analysis has proved that this method can be applied with success even in a species whose genome, at the moment, has not been sequenced.

Assessment of ectomycorrhizal fungal communities in the natural habitats of Tuber magnatum (Ascomycota, Pezizales)

The ectomycorrhizal (ECM) fungal communities of four natural Tuber magnatum truffle grounds, located in different Italian regions (Abruzzo, Emilia-Romagna, Molise, and Tuscany), were studied. The main objective of this study was to characterize and compare the ECM fungal communities in the different regions and in productive (where T. magnatum ascomata were found) and nonproductive points. More than 8,000 (8,100) colonized root tips were counted in 73 soil cores, and 129 operational taxonomic units were identified using morphological and molecular methods. Although the composition of the ECM fungal communities studied varied, we were able to highlight some common characteristics. The most plentiful ECM fungal taxa belong to the Thelephoraceae and Sebacinaceae families followed by Inocybaceae and Russulaceae. Although several ectomycorrhizas belonging to Tuber genus were identified, no T. magnatum ectomycorrhizas were found. The putative ecological significance of some species is discussed.

A realized Tuber <i>magnatum</i> niche in the upper Sinni area (south Italy)

A realized Tuber magnatum niche, in the upper Sinni area (Serrapotamo, south Italy), was studied using geographic information system, direct in situ survey and genetic diversity at DNA marker loci. Truffieres were north facing, associated with a fine loamy-sandy soil bearing high carbonate content over a conglomerate bead-rock substrate. Target area is located in Pavari's cold and medium-cold Lauretum phithoclimatic belts. Ascoma genomic DNA was analyzed and ITS sequences, microsatellites (MA2, MA4 and MA7), along with M13 minisatellite loci, did show low heteozygosity (HE = 0.153). Serrapotamo genotypes did not express localized markers when compared with Piemonte (north Italy) genetic material. ITS marker, monomorphic within T. magnatum, was efficient at distinguishing T. borchii in a mixture of both. Serrapotamo niche represents a unique T. magnatum diversity spot in the southernmost side of the Mediterranean region. Maintaining Serrapotamo T. magnatum diversity by undertaking conservation measures is adviced.

A new species of Melanospora on truffles from China

The new species Melanospora subterranea is described from China, based on morphological and phylogenetic analyses. This is the first record of Melanospora species parasitizing Chinese black and white truffles (Tuber indicum and T. huidongense), and its host range indicates that the new species might be a disease threat to commercially exploited European truffles including Tuber melanosporum and Tuber magnatum. Apparent polyphyly within the Ceratostomataceae can be explained at least in part by inadvertent sequencing of the host fungus instead of the parasite.

Electronic nose and GC–MS analysis of volatile compounds in Tuber magnatum Pico: Evaluation of different storage conditions

The characteristic aromatic composition of white truffles (Tuber magnatum Pico) determines its culinary and commercial value. However modifications of truffle organoleptic proprieties occur during preservation. A study of headspace of white truffles by using Electronic nose (E-nose), gas chromatography–mass spectrometry (GC–MS) and sensory analyses was performed. Truffles were stored at different conditions for 7days: +4 and +8°C wrapped in blotting paper or covered by rice or none of the above. Headspace E-nose measurements and sensory analyses were performed each day. Statistical multivariate analysis of the data showed the capability of E-nose to predict sensorial analysis scores and to monitor aroma profile changes during storage. Truffle’s volatile molecules were also extracted by headspace solid phase microextraction technique and separated and identified by GC–MS. Partial Components Analysis of data was performed. E-nose and GC–MS results were in agreement and showed that truffle storage in paper at +8°C seemed to be the best storage condition.

Authentication of prized white and black truffles in processed products using quantitative real-time PCR

Truffles, such as Tuber magnatum and Tuber melanosporum, are greatly appreciated throughout the world, both as fresh fruiting bodies and as ingredients in processed products. Diagnostic methods are therefore required to check the identity of truffles in this kind of food. The present paper reports the application of microscopic and molecular techniques to authenticate truffle species in commercial products. Through the application of microscopic techniques, it has been possible to distinguish spores in a cream that could be ascribed to the truffle species (T. magnatum, the highest priced truffle) declared on the label and also spores of a less prized and aromatic truffle that was not indicated on the label. Good quality DNA was quickly obtained in a few hours using a kit generally employed for DNA extraction from soil. A new primer pair was developed to authenticate T. magnatum in commercial products and it was employed in a quantitative PCR assay (qPCR). T. melanosporum, which was neither indicated on the label nor recognized in the processed products containing truffles, was also detected in a cream and its amount was quantified by qPCR. This method can therefore be used to detect fraudulent practices and to protect the consumer of truffle delicacies.

Intraspecific genotypic variability determines concentrations of key truffle volatiles

Aroma variability in truffles has been attributed to maturation (Tuber borchii), linked to environmental factors (Tuber magnatum), but the involvement of genetic factors has been ignored. We investigated aroma variability in Tuber uncinatum, a species with wide distribution. Our aim was to assess aroma variability at different spatial scales (i.e. trees, countries) and to quantify how aroma was affected by genotype, fruiting body maturity, and geographical origin.A volatile fingerprinting method was used to analyze the aroma of 223 T. uncinatum fruiting bodies from seven European countries. Maturity was estimated from spore melanization. Genotypic fingerprinting was performed by amplified fragment length polymorphism (AFLP).Discriminant analysis revealed that, regardless of the geographical origin of the truffles, most of the aroma variability was caused by eight-carbon-containing volatiles (C8-VOCs). In an orchard of T. uncinatum, truffles producing different concentrations of C8-VOCs clustered around distinct host trees. This clustering was not associated with maturity, but was associated with fungal genotype.These results indicate that the variation in C8-VOCs in truffles is most likely under genetic control. They exemplify that understanding the factors behind aroma variability requires a holistic approach. Furthermore, they also raise new questions regarding the ecological role of 1-octen-3-ol in truffles.

Biochemical characterization of a sphingomonad isolate from the ascocarp of white truffle (Tuber magnatum Pico)

Available information on bacteria that influence the economically important white truffle (Tuber magnatum Pico) life cycle is scarce. From the ascocarp of white truffle we isolated a strain TMG 022C, capable for growth in nitrogendepleted conditions and assimilation of mannitol and trehalose. According to 16S rDNA sequence phylogeny, the strain was closely related to Sphingobium amiense. The strain had the ability to perform ammonification, reduce nitrate and solubilize Ca3(PO4)2, produce chitinase, lipase, phospholipase and ?-glucanase, but not cellulase, pectinase, protease and siderophores. The results suggest that Sphingobium sp. TMG 022C could have an influence on the Tuber magnatum life cycle through improved mycelium nutrition and ascocarp decomposition.

Physical land suitability map for Tuber magnatum Pico in Piana Crixia municipality territory (Liguria-Italy)

Please click here to download the map associated with this article. Land suitability is the fitness of a given type of land for a specific use. Tuber magnatum Pico is one of the most valuable truffles present in Italy. The objective of this study was to assess the suitability of land to favour the growth of T. magnatum, using detailed soil spatial information, for the area around Piana Crixia (a town in Province of Savona, Italy). The work is based on land evaluation framework promoted by the Food and Agriculture Organization of the United Nations. Attributes of the physical environment (soil and wetness characteristics) were assembled and used for the suitability assessment. Each attribute was mapped using a geographical information system and classified on the basis of predefined requirements. Soil and wetness requirements for T. magnatum were identified using expert knowledge of highly productive truffle grounds and a land suitability map at a scale of 1:10,000 was produced by overlaying the generated soil suitability and wetness suitability maps.

New evidence for nitrogen fixation within the Italian white truffle Tuber magnatum

Diversity of nitrogen-fixing bacteria and the nitrogen-fixation activity was investigated in Tuber magnatum, the most well-known prized species of Italian white truffle. Degenerate PCR primers were applied to amplify the nitrogenase gene nifH from T. magnatum ascomata at different stages of maturation. Putative amino acid sequences revealed mainly the presence of Alphaproteobacteria belonging to Bradyrhizobium spp. and expression of nifH genes from Bradyrhizobia was detected. The nitrogenase activity evaluated by acetylene reduction assay was 0.5–7.5 μmol C 2H 4 h −1 g −1, comparable with early nodules of legumes associated with specific nitrogen-fixing bacteria. This is the first demonstration of nitrogenase expression gene and activity within truffle.

Bacterial and fungal communities associated with Tuber magnatum‐productive niches

Truffles are hypogeous ectomycorrhizal fungi of ecological interest for forestry in soils of the northern hemisphere, and of economical relevance for food markets worldwide. The molecular mechanisms that control truffle body formation are largely unknown, as well as the environmental factors that are likely involved. Among the latter, it has been hypothesized that soil‐borne communities may have an impact on truffle production. To address this question, we investigated bacterial and fungal communities resident in productive versus adjacent non‐productive grounds of the white truffle Tuber magnatum by using PCR‐DGGE. Although bacterial communities were generally highly similar across all samples within the grounds, profiles did cluster according to the productivity of circumscribed niches, and a Moraxella osloensis population appeared to be associated with productive sites. Fungal communities revealed several populations, yet showed no obvious patterns in relation to productivity, although Mortierella and Fusarium oxysporum appeared to be more abundant in the productive area. Our results offer a first glimpse into microbial communities thriving in truffle productive niches, and open the question as to whether microbe‐mediated mechanisms may facilitate/inhibit truffle fruiting‐body production or, vice versa, i.e. whether truffle sporocarps have an impact on the microbes living in the rhizosphere.

Soil analysis reveals the presence of an extended mycelial network in a Tuber magnatum truffle-ground

Truffles are hypogeous ectomycorrhizal fungi. They belong to the genus Tuber and are currently considered a hot spot in fungal biology due to their ecological and economic relevance. Among all the species, Tuber magnatum is the most appreciated because of its special taste and aroma. The aim of this work was to set up a protocol to detect T. magnatum in soil and to assess its distribution in a natural truffle-ground. We used the beta-tubulin gene as a marker to identify T. magnatum in the soil. This gene allowed us to trace the distribution of the fungus over the entire truffle-ground. Tuber magnatum was found, in one case, 100 m from the productive host plant. This study highlights that T. magnatum mycelium is more widespread than can be inferred from the distribution of truffles and ectomycorrhizas. Interestingly, a new haplotype - never described from fruiting body material - was identified. The specific detection of T. magnatum in the soil will allow to unravel the ecology of this fungus, following its mycelial network. Moreover, this new tool may have practical importance in projects aimed to increase large-scale truffle production, checking for T. magnatum persistence in plantations.

Physical characteristics of the soil environment suitable for Tuber magnatum production in fluvial landscapes

Tuber spp. are ectomycorrizal fungi that produce edible ascocarps termed truffles. The most valuable species, T. magnatum, is perhaps the most selective among these for soil environment. Since T. magnatum is often found in fluvial plains, the present study focused on the characterization of the soil physical characteristics suitable for this ectomycorrhizal fungus, and the relationship of these characteristics with fluvial landforms. The investigation was carried out in a truffle-producing area which encompassed the most representative landforms of a fluvial landscape characterized by the presence of Populus deltoides symbionts in both productive and unproductive locations. Soil physical characteristics were determined in productive and unproductive transects according to a stratified random design. Truffle-producing locations displayed a coarser texture, smaller aggregates, a less stable aggregation and a larger volume of soil occupied by highly interconnected macropores. The spatial distribution of this combination of characteristics was then investigated by using a geostatistical approach utilizing clay content and a soil structure indicator as markers. Spatial analysis connected T. magnatum habitats with the soil environment present in river levees, where scattered and chaotic redeposition of solid particles creates very porous, highly aerated surface strata.

Geographical traceability of Italian white truffle (Tuber magnatum Pico) by the analysis of volatile organic compounds

Results are presented that were obtained on the geographic traceability of the white truffle Tuber magnatum Pico. Solid-phase microextraction coupled to gas chromatography/mass spectrometry (SPME-GC/MS) was employed to characterize the volatile profile of T. magnatum white truffle produced in seven geographical areas of Italy. The main components of the volatile fraction were identified using SPME-GC/MS. Significant differences in the proportion of volatile constituents from truffles of different geographical areas were detected. The results suggest that, besides genetic factors, environmental conditions influence the formation of volatile organic compounds. The mass spectra of the volatile fraction of the samples were used as fingerprints to characterize the geographical origin. Next, stepwise factorial discriminant analysis afforded a limited number of characteristic fragment ions that allowed a geographical classification of the truffles studied.

Out of the rivers: are some aquatic hyphomycetes plant endophytes?

Ingoldian fungi, or aquatic hyphomycetes, are asexual microfungi, mostly ascomycetes, commonly occurring in running freshwater. They grow on dead plant material, such as leaves and twigs, and play a major role in nutrient flows in stream ecosystems (Barlocher, 1992). They were discovered and first extensively studied by Ingold (1942) and were thus named "Ingoldian" fungi. Ingold described their abundant multicellular asexual spores of sigmoid or, more typically, tetraradiate shape (Fig. 1). He recognized that they probably arose from multiple convergent evolutions, by secondary adaptation to aquatic life, as recently confirmed by molecular markers (Belliveau & Barlocher, 2005; Baschien et al., 2006). Because of their apparent lack of sexuality, Ingoldian species were placed in asexual genera, such as Tricladium or Tetracladium, based on conidial morphology and/or mode of conidiogenesis. Unexpectedly, several lines of evidence now suggest that some Ingoldian fungi are also plant endophytes, that is, they grow in plants without producing symptoms.[...]

Effect of storage on biochemical and microbiological parameters of edible truffle species

The effects of different storage treatments on the most common edible truffle species, such as Tuber magnatum and Tuber borchii (white truffles), Tuber melanosporum and Tuber aestivum (black truffles), were analysed. Biochemical and microbiological profiles were monitored, in order to evaluate possible alterations during truffle preservation. After harvesting, some fresh samples were kept at 4°C for 30days, other samples were frozen at −20°C for one month, thawed and preserved at 4°C; the remainder were autoclaved.The biochemical parameters studied were sugar and protein content, the activity of some enzymes involved in the central metabolism of the fungi and the electrophoretic pattern of soluble proteins. Total mesophilic bacteria were also counted. The results obtained showed that the storage at 4°C is the treatment that best preserves the biochemical and microbiological characteristics of fresh truffles. Black truffles were more resistant to biochemical spoilage than the white ones, while T. magnatum was the most resistant to microbial spoilage.