Melanosporum Research Articles

Different maturities drive proteomic and metabolomic changes in Chinese black truffle

Chinese black truffle (Tuber indicum) is rich in nutrition. However, commercial interests lead to the aroma components and nutrients of T. indicum being greatly affected by overexploitation without consideration of their maturity. This study investigated the proteomic and metabolomic profiles of truffle fruiting bodies at different maturities using a meta-proteomic approach. Among the 3007 identified proteins, the most up-expressed protein in the mature ascocarps was involved in the peptidyl-diphthamide biosynthetic process, while thiamine metabolism was the most differentially expressed pathway. Furthermore, a total of 54 metabolites identified upon LC-MS differed significantly, with 30 being up-expressed in the mature ascocarps, including organic acids, carnitine substances and polysaccharides. Additionally, the ash, protein, fat, crude fiber and total sugar contents were all higher in the mature ascocarps. Overall, our findings reveal that mature truffles have a higher nutritional value, providing a basis for further exploring protein functionality of T. indicum at different maturities.

Nutritional value and antioxidant activity of Chinese black truffle (Tuber indicum) grown in different geographical regions in China

Nutritional and health-promoting properties of Tuber indicum are still unclear. In this study, total phenol content (TPC) and total flavonoid contents (TFC) were determined by colorimetric methods; free phenolic acids, vitamin D2 and ergosterol content were determined by HPLC; antioxidant activity were evaluated using ABTS, DPPH, and FRAP assays; in vitro anti-inflammatory activity was evaluated by protease inhibitory assay. Our results indicated that geographical origin exhibits a significant impact on the nutritional and pharmaceutical properties of Tuber indicum. The samples collected from Sichuan present significant higher proteins (23.2 g/100 g dw), ash (6.38 g/100 g dw), 1,3:1,6-β-glucan (14.7 g/100 g dw) and ergosterol content (0.76 mg/g dw); whereas the samples collected from Yunnan present the highest amount of pectin (4.52 g/100 g dw), food energy (345.20 kcal/100 g dw), TPC (1.53 mg GAE/g dw), TFC (1.66 mg CAE/g dw) and the highest ABTS and DPPH values, and potent anti-inflammatory effects. In addition, the samples collected from Jilin presented the highest amount of total carbohydrate (51.7 g/100 g dw), reducing sugar (7.3 g/100 g dw) and total phenolic acids (66.76 μg/g dw). These results will enhance current knowledge about nutritional values, chemical compositions, and biological properties of T. indicum.

Characterization of Tuber indicum (Pezizales, Tuberaceae) mycorrhizae synthesized with four host trees exotic to China

The Chinese black truffle Tuber indicum is the main commercial truffle species in China and has strong potential for cultivation. Most studies have focused so far on the production and planting of mycorrhizal seedlings of tree species native to China. Here, we selected four exotic tree species, Quercus pubescens, Q. ilex, Q. palustris and Pinus pinea and inoculated axenically germinated seedlings, five replicates per tree species, with T. indicum spore suspension. As shown by morphological, anatomical and molecular analyses, mycorrhizae were successfully synthesized under greenhouse conditions from 6 months after inoculation and the mycorrhization was stable for at least 24 months in the glasshouse environment. Despite slight morphological variations, T. indicum mycorrhizae were similar on all tree species, i.e. swollen, red-brownish with long hyaline emanating hyphae showing right-angle ramifications. Our observations confirmed the similarity of T. indicum mycorrhizae with those of T. melanosporum regardless of the geographic origin of host trees. Four out of five T. indicum-inoculated pine seedlings were cross-contaminated by T. borchii that was inoculated to another group of P. pinea seedlings raised in the same glasshouse. This is the first study to document the mycorrhization of exotic tree species by T. indicum in China and the first report for Q. palustris. With two successful out of five inoculated seedlings, Q. palustris was less receptive to T. indicum mycorrhization than the other two oak species. Further work is needed to assess whether the T. indicum symbioses obtained here are maintained after planting in the field and if ascomata can be produced by exotic tree species under Chinese environmental conditions.

Tuber melanosporum shapes nirS-type denitrifying and ammonia-oxidizing bacterial communities in Carya illinoinensis ectomycorrhizosphere soils.

BackgroundNirS-type denitrifying bacteria and ammonia-oxidizing bacteria (AOB) play a key role in the soil nitrogen cycle, which may affect the growth and development of underground truffles. We aimed to investigate nirS-type denitrifying bacterial and AOB community structures in the rhizosphere soils of Carya illinoinensis seedlings inoculated with the black truffle (Tuber melanosporum) during the early symbiotic stage.MethodsThe C. illinoinensis seedlings inoculated with or without T. melanosporum were cultivated in a greenhouse for six months. Next-generation sequencing (NGS) technology was used to analyze nirS-type denitrifying bacterial and AOB community structures in the rhizosphere soils of these seedlings. Additionally, the soil properties were determined.ResultsThe results indicated that the abundance and diversity of AOB were significantly reduced due to the inoculation of T. melanosporum, while these of nirS-type denitrifying bacteria increased significantly. Proteobacteria were the dominant bacterial groups, and Rhodanobacter, Pseudomonas, Nitrosospira and Nitrosomonas were the dominant classified bacterial genera in all the soil samples. Pseudomonas was the most abundant classified nirS-type denitrifying bacterial genus in ectomycorrhizosphere soils whose relative abundance could significantly increase after T. melanosporum inoculation. A large number of unclassified nirS-type denitrifying bacteria and AOB were observed. Moreover, T. melanosporum inoculation had little effect on the pH, total nitrogen (TN), nitrate-nitrogen (NOn}{}{}_{3}^{-}-N) and ammonium-nitrogen (NHn}{}{}_{4}^{+}-N) contents in ectomycorrhizosphere soils. Overall, our results showed that nirS-type denitrifying bacterial and AOB communities in C. illinoinensis rhizosphere soils were significantly affected by T. melanosporum on the initial stage of ectomycorrhizal symbiosis, without obvious variation of soil N contents.

Synthesis and ultrastructural observation of arbutoid mycorrhizae of black truffles (Tuber melanosporum and T. aestivum)

Arbutus unedo (the strawberry tree) is a Mediterranean shrub which forms arbutoid mycorrhizae with a variety of Asco- and Basidiomycetes. After the discovery of the mycorrhizal symbiosis between A. unedo and Tuber borchii, in this study, arbutoid mycorrhizae were synthetized in greenhouse with Tuber aestivum and Tuber melanosporum. Six months after inoculation, both species colonized the roots of all inoculated A. unedo seedlings, but mature mycorrhizae were only observed after 12 months. Ultrastructure analysis of Tuber arbutoid mycorrhizae was described for the first time, showing, as observed in typical endosymbiosis, a rearrangement of host cells and the creation of an interface compartment with both truffle species. Immunolabelling experiments suggested that pectins are not present in the interface matrix surrounding the intracellular hyphae. Thus, the ability to establish symbiosis with A. unedo seems to be a common feature in the genus Tuber, opening up the possibility to use this plant for mycorrhization with valuable truffles. This could represent an important economic opportunity in Mediterranean areas by combining the production of truffles, edible fruits and valued honey.

Hypobaric Packaging Prolongs the Shelf Life of Refrigerated Black Truffles (Tuber melanosporum).

Black truffle (Tuber melanosporum Vitt.) is a fine agro-food product known for its unique aroma and very limited shelf life (maximum of 5–7 days, room temperature). Hypobaric packaging at 30 kPa, a mix of 1% O2/99% N2, and 40% CO2/60% N2 were studied to prolong the shelf life of black truffle at 4 °C in sealed polypropylene vessels, compared to normal atmosphere. Epiphytic microbial population, firmness, weight loss, CO2 formation, and sensory properties were monitored weekly up to 35 days of storage and were related to the volatile profile. Principal components analysis revealed good correlation between the storage time and the decrease of firmness, and the increase of the microbial count and CO2 production. Only truffles stored under hypobaric conditions showed an acceptable quality after 14 days storage. Hypobaric packaging is a cheap strategy to prevent the swelling of vessels caused by respiration and can reduce the deviation from the high-quality level of the fresh product from one to at least two weeks.

Persistence of Tuber melanosporum in truffle orchards in North Carolina, USA.

A survey was conducted to determine the persistence of mycorrhization by Tuber melanosporum in truffle orchards established with European and American species of oak and common hazel trees in North Carolina. The trees had reportedly been inoculated and colonized by T. melanosporum prior to planting. Root samples were collected from 95 trees among seven orchards in 2015 and roots were analyzed by morphology and quantitative PCR. Samples that tested negative for T. melanosporum or where ectomycorrhizal morphology was not observed were analyzed by sequencing to identify the mycorrhizal fungal symbiont present. The presence of T. melanosporum was detected in all seven orchards. In six orchards, T. melanosporum was detected on all trees, but in only two of fifteen trees in one orchard. Other species of Tuber including T. brennemanii, T. canaliculatum, and T. lyonii, species of Scleroderma, and members of the Pezizales were also detected by sequence analysis. Sporocarps of T. aestivum and T. brumale were found in 2017 and 2018 in separate orchards in North Carolina after the survey was conducted. Overall, results indicate that T. melanosporum has persisted in truffle orchards sampled in North Carolina. Indigenous and contaminating fungal species, including Tuber species, were also detected and present a challenge to the truffle industry in North Carolina.

Tree ring and water deficit indices as indicators of drought impact on black truffle production in Spain

Black truffle is a highly-prized fungus that constitutes an important economic resource in many Mediterranean forests of southern Europe. Black truffle production in these forests and in cultivated truffle orchards is subject to important interannual variations linked to climatic factors, among which summer water shortage is particularly relevant in dry regions such as Mediterranean Spain. Thus, in recent years irrigation has become widespread in Spanish black truffle orchards, although no long-term proxies of black truffle production exist and scientific guidelines for the irrigation of these orchards are lacking. In this study, we explore the possibilities and limitations of pine tree-ring width data (seasonal wood production) and agroclimatic indices to predict black truffle production in Spain, while gaining more in-depth knowledge on water requirements of truffle production. For this purpose, we used the national annual estimates of black truffle production and compared these values with several tree-ring width series, monthly climatic factors, and water balance-based indices. We found a strong linkage between summer water availability, black truffle production and Mediterranean pine latewood formation, with summer drought intensity reducing both black truffle and Pinus pinaster latewood production. The adjusted latewood index for P. pinaster and the accumulated water deficit from April to September were robust predictors of black truffle production. The predictive skills of these two variables were further confirmed with a calibration-verification technique. These variables can be used as climatic proxies of black truffle production in agronomic or silvicultural studies, in a sector where no large-scale network for monitoring soil water content exists, and many truffle orchards are small and have low possibilities for modernisation.

Use of Inoculator Bacteria to Promote Tuber melanosporum Root Colonization and Growth on Quercus faginea Saplings

Research Highlights: Mycorrhizal helper bacteria (MHB) promote mycorrhization processes and are commonly found in the mycorrhizosphere of fungi, such as the edible hypogeous fungus Tuber melanosporum Vittad. Background and Objectives: The effectiveness of MHB in promoting the mycorrhization process and the root development of Portuguese oak (Quercus faginea Lam.) 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 the T. melanosporum niche (i.e., Pseudomonas fluorescens, Pseudomonas putida, and Bacillus amyloliquefaciens) and two different bacterial inoculation times (one month and nine months after fungal inoculation) under glasshouse conditions. Results: Only P. fluorescens had 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 of P. fluorescens with T. melanosporum improved 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 that P. fluorescens bacteria have a potential commercial application as a treatment for truffle-inoculated seedlings to improve both seedling quality and mycorrhizal colonization under nursery conditions.

Food Authentication: Truffle (Tuber spp.) Species Differentiation by FT-NIR and Chemometrics.

Truffles are certainly the most expensive mushrooms; the price depends primarily on the species and secondly on the origin. Because of the price differences for the truffle species, food fraud is likely to occur, and the visual differentiation is difficult within the group of white and within the group of black truffles. Thus, the aim of this study was to develop a reliable method for the authentication of five commercially relevant truffle species via Fourier transform near-infrared (FT-NIR) spectroscopy as an easy to handle approach combined with chemometrics. NIR-data from 75 freeze-dried fruiting bodies were recorded. Various spectra pre-processing techniques and classification methods were compared and validated using nested cross-validation. For the white truffle species, the most expensive Tuber magnatum could be differentiated with an accuracy of 100% from Tuber borchii. Regarding the black truffle species, the relatively expensive Tuber melanosporum could be distinguished from Tuber aestivum and the Chinese truffles with an accuracy of 99%. Since the most expensive Italian Tuber magnatum is highly prone to fraud, the origin was investigated and Italian T. magnatum truffles could be differentiated from non-Italian T. magnatum truffles by 83%. Our results demonstrate the potential of FT-NIR spectroscopy for the authentication of truffle species.

Colonization by Tuber melanosporum and Tuber indicum affects the growth of Pinus armandii and phoD alkaline phosphatase encoding bacterial community in the rhizosphere

The synthesis of truffle ectomycorrhizae and the ecology of truffle-colonized seedlings in the early symbiotic stage are important for the successful truffle cultivation. In this study, two black truffle species, Tuber melanosporum and Tuber indicum, were selected to colonize Pinus armandii seedlings. 2, 4, 6 and 8 months after inoculation, the growth performance of the host and the rhizosphere soil properties were detected. The dynamic changes of two mating type genes in substrate were also monitored to assess the sexual distribution of truffles. Additionally, the variation of soil bacterial communities encoded by phoD alkaline phosphatase genes was investigated through next-generation sequencing. The results indicated that both T. melanosporum and T. indicum colonization promoted the growth of P. armandii seedlings to some extent, including improving their biomass, total root surface area, root superoxide dismutases and peroxidase activity. The organic matter and available phosphorus in rhizosphere soil were also significantly enhanced by two truffles’ colonization. The phoD-harboring bacterial community structure was altered by both truffles, and T. melanosporum decreased their diversity or richness on the 6th and 8th month after inoculation. Pseudomonas, Xanthomonas, and Sinorhizobium, a N2-fixer with phoD genes, were found more abundant in truffle-colonized treatments. The mating type distribution of the two truffles was uneven, with MAT1−1-1 gene occupying the majority. Overall, T. melanosporum and T. indicum colonization affected the micro-ecology of truffle symbionts during the early symbiotic stage. These results could give us a better understanding on the truffle-plant-soil-microbe interactions, which would be beneficial to the subsequent truffle cultivation.

The influence of forest surroundings on the soil fungal community of black truffle (Tuber melanosporum) plantations

Black truffles are a highly valued non-wood forest product. The success of truffle plantations is raising 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 whose fungal community was less affected by the distance to the forest. No association 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.

Species and geographic variability in truffle aromas

The gastronomic relevance and price of truffles are related mainly to its unique aroma. In this study, we explore the impact that different volatile compounds have on the aroma quality of fresh truffles using gas chromatography-mass spectrometry (GC-MS). Four hundred sixty fresh ascocarps of nine truffle species (Tuber aestivum, Tuber magnatum, Tuber melanosporum, Tuber mesentericum, Tuber brumale, Tuber excavatum, Tuber rufum, Tuber indicum and Tuber macrosporum) harvested in 2018/19 and 2019/2020 from 11 different countries (Slovenia, Croatia, Bosnia in Herzegovina, Macedonia, Italy, Spain, France, United Kingdom, Germany, Poland and China) were collected. Our investigation included the classification of species based on their aroma profile, a study of the differences in the volatile organic composition of truffle species over a geographical area, and, in more detail, a study of T. aestivum from four natural truffle growing sites in Slovenia. Our models can distinguish between groups, with small classification error. These models could form the basis of a predictive framework to detect fraud concerning truffle products and to determine the influence of different growing parameters on the aroma profile of truffles.

The influence of forest surroundings on the soil fungal community of black truffle (Tuber melanosporum) plantations

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.

Dioscorea saponin transforms the structure of truffle exo-polysaccharide and enhances its antioxidant activity

Dioscorea saponin (DS) can increase the exo-polysaccharide production of Tuber melanosporum. In the present study, we assessed the effect of DS on the structure and antioxidant activity of exo-polysaccharide. In the absence of DS, only one exo-polysaccharide (TP1) composed of mannose, rhamnose and glucose was isolated. However, two exo-polysaccharides (STP1 and STP2) were isolated in the presence of DS. STP1 was composed of glucose, galactose and arabinose, and STP2 consisted of rhamnose, glucose, galactose and arabinose. The skeletal structure of TP1, STP1 and STP2 was composed of α-d-glucopyranose. The antioxidant activity of exo-polysaccharide exhibited a concentration-dependent manner. The DPPH radical-scavenging rate (61.37%) and total antioxidant activity (50.02%) of STP were higher compared with TP1. The STP increased the DPPH radical-scavenging rate depending on the increase of the maximum rate of the reaction at saturating substrate concentrations (kcat), while STP increased the reducing power depending on the kcat and affinity of substrate to STP. The inhibitory action of STP on hydroxyl radical generation depended on the blockage of Fe2+ by STP, making it unable to react with H2O2 to form ·OH, and STP could bind to the Fe2+- H2O2 complex and prevent the Fe2+ from turning H2O2 into product.

Food Authentication: Identification and Quantitation of Different Tuber Species via Capillary Gel Electrophoresis and Real-Time PCR.

Truffles are hypogeous fungi mainly found in Europe and Asia. Due to their special aroma and taste, some truffle species are sold on the international market at an extremely high price. Among the economically relevant species, the white Alba truffle (Tuber magnatum) and the black Périgord truffle (T. melanosporum) are the most appreciated species. The fruiting bodies of the Asian black truffle are morphologically very similar to T. melanosporum, and those of the Bianchetto truffle (T. albidum Pico) are similar to T. magnatum, but are of little economic value. Highly valued species are adulterated with cheaper ones, especially. Because of this problem, the aim of this study was the development of methods for detecting possible admixtures to protect consumers from fraud. This study is based on seven different truffle species (117 fruiting bodies) from different growing regions. Additionally, selected truffle products were included. Using this material, a real-time PCR (polymerase chain reaction) assay allowing the detection and quantitation of Asian black truffles in T. melanosporum up to 0.5% was developed. In addition, a capillary gel electrophoresis assay was designed, which allows the identification and quantitation of different species. The methods can be used to ensure the integrity of truffle products.

The effect of fungi and bacteria symbiosis with switchgrass (Panicum virgatum L.) root system

Purpose. To establish the symbiotic effect of symbiosis of fungi and bacteria with the root system of switchgrass (Panicum virgatum L.) in improving their growth and development and increasing productivity.Methods. Field, laboratory and statistical.Results. With the use of mycorrhizal fungi and nitrogen-fixing bacteria, positive results were obtained on their influence on the growth and development of plants and the yield formation. In particular, the leaf surface area in variants with the fungus Trichoderma harzianum Rifai. (Mycofriend) and Tuber melanosporum Vittad. (formulation Mikovital) and bacteria Bacillus subtilis Cohn. (formulation Florobacillin) for accounting for 30, 60, 90 and 120 days of the growing season was 3.2–13.2% higher compared to the control. Similarly, the mass of leaves and root system exceeded the control indicators by 5.1–24.4%, respectively. The height of plants in these terms of accounting was 4.4–13.7% higher than in the control. In addition, in these variants, the soil retention increased by 6.7–25.0%, and the proportion of soil lumps smaller than 0.25 mm decreased by 3.2–8.5% compared to the control. The yield of dry mass of switchgrass in variants with mycorrhizal fungi and nitrogen-fixing bacteria was 0.88–2.64 t/ha higher than in the control.Conclusions. Use of mycorrhizal fungi Trichoderma harzianum Rifai. and Tuber melanosporum Vittad. (formulations Mykofrend and Mikovital), as well as nitrogen-fixing bacteria Bacillus subtilis Cohn. (formulation Florobacillin) at their radical introduction into the soil contribute to the improvement of growth and development of switchgrass plants and increase the yield of dry biomass.

Edaphic and temporal patterns of Tuber melanosporum fruitbody traits and effect of localised peat-based amendment

In Tuber melanosporum cultivation, fruitbody traits are gaining relevance due to their increasing prominence on prices. We investigated the edaphic and temporal patterns of fruitbody traits and characterised the effect of truffle nests (localised peat-based amendment supplemented with T. melanosporum spores) on traits. We monitored fruitbody traits throughout two fruiting seasons in three blocks along a soil gradient. Each trait followed specific edaphic and temporal patterns. The number of fruitbodies per dig and spore maturity followed characteristic within-season trends, whereas fruitbody weight and infestation by truffle beetles were subject to complex interactions among edaphic and temporal variables, suggesting a relevant influence of annual environmental conditions. The application of truffle nests increased fruitbody depth, improved its shape and decreased infestation by truffle beetles. Nests increased the number of fruitbodies per dig, but only in two of the soils, suggesting a relevant role of the bulk soil/substrate interface in fruiting initiation. These results outline a complex scenario, with each trait being differently affected by environmental factors. In this scenario, nests proved to effectively modify several traits, although not always in the desired direction.

Multi-platform metabolomic approach to discriminate ripening markers of black truffles (Tuber melanosporum)

Black truffle is characterized by a black ascocarp and white veins. This hypogeous fruit body is known for its aroma. Understanding metabolic variation during ripening can shed light on truffle biology. In this work, the comprehensive polar metabolome and the volatile organic compounds of T. melanosporum were studied at different ripening stages by means of a metabolomic approach using GC–MS. Multivariate statistical data analysis indicated that the metabolic profile changed during ripening and that the metabolites that mostly discriminated truffles in the early ripening stages belonged to the classes of carbohydrates, while free fatty acids and amino acids, among which precursors of VOCs, characterized the late stages of ripening. Principal component analysis of the volatilome indicated that dimethylsulfide and dimethyldisulfide characterized most of the samples collected in December-January, while 1-octen-3-ol samples collected in February-March.

Variability and trends of black truffle production in Spain (1970-2017): Linkages to climate, host growth, and human factors

Black truffle (Tuber melanosporum) is a highly-appreciated fungus that grows below ground during several months, undergoing a series of morphogenetic stages before it is harvested in late autumn or winter. Black truffle production in Spain has been subject to important temporal variation in recent decades. The records of the Spanish Truffle Growers Association from 1970 to 2017 were analysed using additive models to investigate the relative roles of climate, host tree growth and other environmental and human factors on the variability and trend of fruiting body production and phenology. Climatic factors largely explained the variability in annual truffle production, but not the major time trend observed in the studied period. Temperature and precipitation during fruiting body development showed the highest relationship with truffle production. Atmospheric evaporative demand during fruiting induction and temperature during maturation showed a significant relationship to how truffle production was distributed throughout the fruiting season. The relationship between truffle production and host growth was mostly explained by summer rainfall and by temperatures in several periods spanning from host tree bud burst to fruiting body ripening. The temporal trend of Spanish truffle production in the last decade reflected the recent transition from a wild harvest to an agricultural production, with an abrupt increase in annual production and a decrease in year-to-year variability. In the context of the expected evolution of regional climate according to current models, our results point to drier and warmer summer conditions as major threats to truffle production in Spain. Spring and autumn warming could induce an advance in the mean day of truffle fruiting.