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Entry

The Mysteries of the White Truffle: Its Biology, Ecology and Cultivation

1
Department of Agricultural and Food Sciences, University of Bologna, Viale G. Fanin 44, 40127 Bologna, Italy
2
Truffles & Mushrooms (Consulting) Limited, P.O. Box 268, Dunedin 9054, New Zealand
*
Author to whom correspondence should be addressed.
Encyclopedia 2022, 2(4), 1959-1971; https://doi.org/10.3390/encyclopedia2040135
Submission received: 16 October 2022 / Revised: 25 November 2022 / Accepted: 2 December 2022 / Published: 8 December 2022
(This article belongs to the Collection Encyclopedia of Fungi)

Definition

:
Tuber magnatum Picco is the most expensive of the truffles and a great deal of research has been carried out in an attempt to solve the mysteries of its ecology and biology. However, considerable work remains to be done particularly on those secrets of its life cycle that remain a mystery. It is known that T. magnatum is heterothallic, but it has yet to be determined how fertilization occurs between the two strains of different mating types. It is also known that the white truffle is an ectomycorrhizal fungus, and its mycorrhizas can be produced in greenhouses, but then they seem to disappear in the field. The role of other soil microorganisms, fungi and bacteria, on its soil mycelial development and fructification is intriguing but is far from being completely understood. All these uncertainties have made the cultivation of T. magnatum extremely difficult and only recently have we had the scientific proofs that it is possible. Even so, many questions remain unanswered and the management practices of T. magnatum plantations are still to be better defined to also enable the taming of this truffle.

Graphical Abstract

1. Introduction

Truffles are fleshy ascomycetous fungi that generally fruit underground. The spores are sequestered in the fruiting body (the ascoma or ascocarp), which consists of a more or less subspherical mass. Many researchers prefer to consider as “true truffles” only the Ascomycota in the genus Tuber belonging to the Tuberaceae family and in the order Pezizales [1]. There are more than 180 species, all characterized by an ectomycorrhizal habit and naturally are mostly restricted to the Northern Hemisphere [2]. The phylogeny of the genus has been studied by many authors [3,4,5] with the most recent by Bonito et al., 2013 [2], which provided a complete phylogenetic analysis of the genus and its recognized 11 main clades: Aestivum, Rufum, Excavatum, Gibbosum, Japonicum, Puberulum, Macrosporum, Maculatum, Multimaculatum, Melanosporum and Gennadii. Although all the Tuber species are edible, only four are considered culinary delicacies and command really high prices: Tuber melanosporum Vittad. (Périgord black truffle) in the Melanosporum clade, Tuber borchii Vittad. (Bianchetto truffle) in the Puberulum clade, Tuber magnatum Picco (Italian white truffle) and Tuber aestivum Vittad. (Burgundy truffle) which are both included in the Aestivum clade.
Undoubtedly, T. magnatum ranks above the others because of its intense aroma and unique flavor. As a consequence, Italian retail prices for T. magnatum are higher than for any other truffle and make it one of the world’s most expensive foods [6], with prices ranging from 1000 to 6000 EUR kg−1 [7] and a business of about 0.9 billion EUR year−1 [8].
In poor production years such as 2007 and 2021 [9], when dry summers reduced production, prices reached 7000 EUR kg−1, and outside of Italy in upmarket stores such as Harrods in London, prices reached dizzying heights. In this entry, the distinctive morphological characters of this truffle are described as well as its biology and ecology. The current status of its cultivation is reported, which emphasizes the gaps in our knowledge that actually limit the possibility of taming this truffle in contrast to the other European species of Tuber.

2. Morphology

Tuber magnatum is a “white truffle” because as well as several other Tuber spp. (Tuber borchii, Tuber dryophilum Tul. & C. Tul. and Tuber puberulum Berk. & Broome) it is characterized by smooth, pale-colored ascomata. In contrast, the majority of other edible truffles (e.g., T. melanosporum, T. aestivum and Tuber macrosporum Vittad.) are called “black truffles” on account of their brown, black and warty surfaces. The ascomata of T. magnatum are generally smaller than those of European black truffles (T. melanosporum, T. aestivum and T. brumale Vittad.) but somewhat larger than those of other white truffles (T. borchii, T. maculatum Vittad. and others). They weigh from just a few grams to, in rare cases, more than a kilogram. They are distinguished by smooth to suede-like surfaces and their color varies from pale yellowish brown to yellow ochre, olivaceous or greenish grey (Figure 1a). Sometimes, they have black or brownish spots but can be tinged pink (Figure 1b,c) which Amicucci et al. (2018) [10] identified as corresponding to some carotenoid-producing bacteria of the genera Microbacterium and Chryseobacterium. On the other hand, Ratti et al. (2016) [11] hypothesized that the brown spots may be caused by mycoviruses included in the Endornavirus genus. The peridium is 250–1250 µm thick and its thickness seems to be related to the origin of the ascoma [12]. It is formed of small subspherical cells measuring (3–) 9–15 µm by (3–) 6–12 (–13) µm.
The gleba contains, fine, clear veins, which are light-hazel-colored at maturity. In the case of T. magnatum, one to three (rarely four) spores are enclosed in each ascus. The spores are round or broadly elliptical, yellowish or yellow-brown measuring (20–) 25–32 (–37) µm by (15–) 20–30 (–35) µm (without ornamentation). The surface of the spores is characterized by a special ornamentation, a reticulum that reaches 3 to 5 µm in height, with wide polygonal meshes, with two to four along the greatest diameter (Figure 1d) [13].
The mycelium of T. magnatum was first described by Fontana (1968) [14] after examining just a few hyphae originating from the glebal tissue. Later, Mischiati and Fontana (1993) [15] reported to have isolated T. magnatum mycelium from mycorrhizas. However, a few years later, the same authors showed by genetic analyses that this mycelium did not belong to T. magnatum but to other white truffles [16]. Our recent morphological analyses (data not shown) [17] confirmed that T. magnatum mycelium showed the morphological structures typical of the mycelia of Tuber species such as numerous vesicles, rare anastomoses and hyphal aggregates (Figure 1f–h) [18].
Tuber magnatum mycorrhizae are similar to ectomycorrhizas formed by other Tuber spp. They show monopodial ramifications, range between simple and irregular pinnate and are single or in small groups [16]. The color is paler than in other Tuber mycorrhizas, especially in the young ones which are yellow-grey or amber, often with darker markings due to tannin deposits in the innermost mantle layer adjacent to root cells (Figure 1e). The surface may be smooth or may protrude emanating hyphae and very frequently hyaline, long, ramified cystidia, which are characteristic of T. magnatum mycorrhizas. The mantle surface is pseudoparenchymatous and epidermoid and consists of cells with an irregularly sinuous outline or tending to polyhedral. Longitudinal and cross sections reveal that the pseudoparenchymatous mantle is arranged in 5–6 layers of cells, 20–30 µm thick. It is possible to distinguish the inner layer, because it has a cytoplasmic content, while the outer one is empty. The Hartig net infects only the outer epidermal cell layer [16,19].

3. Aroma

Tuber magnatum, like all truffles, has the spores sequestered in the hypogeous ascoma. This makes it impossible for the truffle to actively discharge its spores and to disseminate them by wind as so many other members of the Pezizaceae family rely on. Instead, they produce strong aromas, which attract mycophagous animals (mammals, arthropods and mollusks) [20,21] which disseminate their spores. The aroma of the white truffle is characteristic and dominated by the volatile component 2,4-Dithiapentane also known as bis(methylthio)methane. More than 60 additional volatile organic compounds (VOCs) add to the complexity of the white truffle aroma, although only 11 of them are sufficiently concentrated to be perceivable by the human nose [22,23]. Among them is a 3-(methylthio) propanal with a potato-like aroma, a 2- and 3-methylbutanal with a malty aroma, a 2,3-butanedione with buttery tones, in addition to 2,4-dithiapentane which has sulphury and garlic-like aromas. Among the nonvolatile compounds is an amine-like compound with a sperm-like aroma identified as 3,4-dihydro-2(H) pyrrol (1-pyrroline) [22]. Regrettably all the commercial white-truffle-flavored products are added with an inappropriate and excessive quantity of synthetic 2,4-dithiapentane and these do not present the complexity and quality of natural truffle aromas [24,25]. In the future, natural truffle aroma volatiles could be potential alternatives to replace the existing synthetic aromas [26], but these have yet to be commercially applied.
Environmental factors can also influence the range of organic volatiles, so harvesting location and picking season are involved in the composition of aromas [23,27,28,29]. Furthermore, the complex aroma of T. magnatum does not depend only on its native compounds, but also on the microorganisms, in particular yeast and bacteria, that live within the ascocarps [30,31]. Although the origins of 2,4-dithiapentane are currently unknown, one possibility is that it may be produced by Betaproteobacteria inside T. magnatum fruiting bodies [31], similar to the one of the thiophene derivatives which originate from bacteria inhabiting T. borchii [32]. Moreover, during prolonged storage of T. magnatum fruiting bodies, there are changes in the microbial communities and with them, volatile profiles, due the formation of spoilage volatile compounds [33] which reduce quality. Postharvest storage conditions may also bring about changes in the truffle aroma [34].

4. Biology

The life cycles of the truffles are not fully understood. Many authors have studied the process that could lead to ascocarp formation [35,36,37,38]. Until 2005, T. magnatum was assumed to be self-compatible or a highly inbred species. This was supported by genotyping using codominant markers, since no heterozygous ascocarps were detected [39,40]. However, later, extensive genetic exchange was detected in the species populations [41], in contrast with previous ideas. Moreover, the SSR genotyping of gleba and asci separately [42] suggested the hypothesis that the sterile hyphae of the gleba, which represent the majority of T. magnatum ascocarps were composed of haploid maternal material, while ascospores contained both paternal and maternal information. Eventually the genome sequence confirmed that T. magnatum, like other Tuber spp., was heterothallic [43]. T. melanosporum and T. borchii mating-type studies with SSR genotyping revealed that ectomycorrhizas and gleba were both formed by a haploid mycelium of the same maternal mating type, instead of spores containing several different genotypes [38,44,45]. However, one question remains unanswered: what is the origin of the male genotype?
Field studies have shown the formation of mycelial mats in T. borchii producing areas producing hyaline and obovate mitospores (conidia) having holoblastic origin in repeatedly branched conidiophores [46,47]. These mitospores seem unable to germinate so it has been suggested they may have a reproductive role and, as in some other ascomycetes, act as spermatia [47]. Similarly, newly productive New Zealand T. borchii truffières and one T. borchii truffière in eastern Tibet also appear to show the early stages of fruiting are also associated with strange mats of hyphae [48], similar to those described by Healey [47]. Although these “conidia” have not been found associated with other economically important European species of Tuber [17], we cannot exclude that they are present because they are simply too difficult to detect in soil. Similar structures have also been found in the in vitro mycelium of Tuber japonicum Hir. Sasaki, A. Kinosh & Nara [49], but never on T. borchii mycelium in vitro conditions [17].
Other postulates might be advanced regarding the identity of the paternal partner: they are mycelia from nearby ectomycorrhizas [50,51], free living mycelia in soil [51], germinating ascospores [20,38,52] or mycelia that exist as endophytes in nonhost plants [53]. This last hypothesis has been rejected for T. aestivum and T. melanosporum [54].

5. Distribution and Ecology

Tuber magnatum has long been considered an almost exclusive Italian truffle restricted to the north and center of the country with smaller patches, in Istria, Croatia southeastern France and the Ticino Canton of Switzerland [13]. However, recent studies have also found it in Sicily, the Geneva Canton of Switzerland [55], Hungary and several Balkan regions [56]. Surprisingly it has also been found in Thailand [57]. It can also be found in Italy in Summer (from July) but generally these truffles do not mature until early autumn (September–October) [58]. These early truffles are generally more superficial (5–10 cm deep) and for this reason and the high temperatures they are exposed to, they often suffer from bacterial rot and insect damage and hence are of low quality. During the height of the season (October to December) the ascomata are usually deeper (10–30 cm) and in some cases, for example under small landsides, they can also be found as deep as 80 cm under the soil surface.
Truffles are mycorrhizal hypogeous fungi, so the host plant and the pedoclimatic characteristics are the most important and most studied ecological factors that determine their development. Tuber magnatum grows in well-drained and well-structured marls, without gravels, but seems better adapted than the other truffles to clay soils. The most suitable soil composition is more or less equal proportions of sand and clay. The optimal pH varies from neutral to moderately alkaline and characterized by a high degree of base saturation and sufficient water throughout the year [59,60]. This species tends to be found where the summer temperatures are about 20 °C [60]. Soils suitable for T. magnatum mainly belongs to Calcaric Fluvisols, Colluvic Calcaric Regosols and Fluvic Eutric Cambisols [61]. It is also associated with stagnant surface water, very soft soils and more than 15 % of the soil volume occupied by interconnected macropores. Ideal places are the banks of rivers or other waterways. Other areas include forest margins and where the soil is disturbed or under isolated trees. The constant presence of water is obligatory and encourages dense canopy cover [61].
T. magnatum is primarily associated with Alnus cordata Desf. (Italian alder), Corylus avellana L. (hazelnut), Ostrya carpinifolia Scop., Populus alba L. (white poplar), P. tremula L. (European trembling aspen), P. nigra L. (Lombardy poplar), Quercus cerris L. (Turkish oak), Q. ilex L. (holm oak), Q. pubescens Willd. (downy oak), Q. robur L. (English or common oak), Salix alba L. (white willow), S. caprea L. (pussy willow), Tilia cordata Mill. (small-leaved lime), T. platyphyllos Scop. (large-leaved lime) [13] and Fagus sylvatica L. [55]. It is also, though rarely, found under Pinus spp. [17] but the ectomycorrhizal association with conifers has never been verified using molecular tools.
Other nonectomycorrhizal plants and in particular scrubby species such as Cornus sanguinea L., Rubus ulmifolius Schott., Rosa canina L., Crataegus monogina J acq. and Juniperus communis L. [62] seem to play a key role in T. magnatum ecology. These plants perhaps modify the soil microclimate creating favorable conditions for the development of T. magnatum mycelium. Moreover, these plants may also host T. magnatum mycelium as endophyte preserving it. While this has yet to be verified for T. magnatum, several other Tuber species such as T. melanosporum, T. aestivum and T. borchii have been shown to form symbiotic associations with nonmycorrhizal plants including orchids [54,63,64,65,66,67]. The Tuber mycelium association with ectomycorrhizal plants and traditionally considered nonhost plants form a common mycorrhizal network which could play important roles in nutrient and signal transportation between a range of plants [68]. Strangely, T. magnatum ascoma production occurs in areas where its mycorrhizas are rare or even absent [69,70], as well as in productive patches [70].
Thanks to qPCR and its optimization for T. magnatum DNA quantification [71], the amount of white truffle mycelium in soil was investigated as well as its distribution in the soil. These studies revealed that T. magnatum mycelium was present from within 100 m of the nearest productive tree [72] and its amount was related to depth. In fact, at 20–30 cm, the mycelial density was significantly higher than at 10–20 cm [60]. Although, it has not been investigated, T. magnatum mycelium may grow at deeper than 30 cm considering that its ascomata were collected as deep as 80 cm [73]. At lower depths, the soil layers are less disturbed and at such depths may protect the mycelium from environmental stress such as high temperatures or drought and may reduce competition with other organisms. This idea is supported by the elevated sensitivity of T. magnatum to environmental stresses occurring during hard winters and dry summers [74]. The mycelium reaches the best growth rate in spring [75]. In that period, temperatures and water availability increase and the host plant sprouts out and restarts its activity after winter [76]. A temperature of 20 °C and a water content near saturation are the best parameters for the white truffle mycelium growth [60]. Marjanović et al. (2015) [59] defined T. magnatum as a species that needed a high level of water availability and was hypo-oxygenation-tolerant.
The microbiome and in particular bacteria seem to have not only a key role in T. magnatum aroma biosynthesis (see Section 3) but also in its mycelium soil development, mycorrhiza formation and fruiting body formation and nutrition [77,78].
A diverse microbial population has been found in T. magnatum ascomata [23,79,80,81,82]. Microorganisms associated with the truffle ascocarps seem to have a potential role in nitrogen fixation as shown in studies carried out on several Tuber species. Barbieri et al. (2010) [81] identified the nitrogenase gene nifH belonged to Bradyrhizobium spp. inside the ascocarps, and the nitrogen fixation yield was shown to be comparable with early nodules of legumes associated with specific nitrogen-fixing bacteria [81,83,84]. Bacteria can colonize the ascoma at the primordium stage [85] and penetrate from the soil. Then, they can be selected by the fungus, reducing their biodiversity into the fruiting bodies irrespective of the soil microbial population. Proteobacteria (Alphaproteobacteria and Gammaproteobacteria) seem to be the most relevant group of truffle microorganisms followed by Actinobacteria and Firmicutes [33,85,86,87]. Bradyrhizobium is the most abundant genus which is linked to its nitrogen-fixation activity. Actinobacteria may also be associated with the truffle’s nutritional requirements. Isolates with sequence similarities to Curtobacterium flaccumfaciens and Rhodococcus sp. were isolated from ascomata of T. magnatum; they can solubilize Ca3(PO4)2 in a way that is dependent on the nitrogen and carbon sources present. Furthermore, they can produce chelating compounds, perform ammonification and degrade β-glucan. These bacteria metabolize different substances and can support the white truffle in its development: C. flaccumfaciens decomposes chitin, pectin, lipids and proteins, while Rhodococcus sp. exhibits urease activity. The nutrition function is not the only one: Rhodococcus isolates inhibited Verticillium leptobactrum. In this way, it can protect the fungus from degrading organisms [88].
Giorgio et al. (2022) [89] showed that although soil type affected the taxonomic structure of the soil microbial communities in productive patches, T. magnatum ascomata had a common core of microbiota. However, inside the ascomata, there were also variable bacterial taxa which were associated with specific environmental conditions [82]. In the future, this variable fraction of bacterial communities may be used to track the geographic origin of T. magnatum ascomata [78].
Tuber magnatum is also associated with specific fungal communities. Leonardi et al. (2013) [70] found that the ectomycorrhizas formed by fungi of the Thelephoraceae, Sebacinaceae and Inocybaceae families were the most abundant within the T. magnatum ascoma productive points. In contrast, the mycorrhizas formed by Russulaceae were more common in unproductive locations [70]. The presence of specific fungal species may be a bioindicator of suitable habitats for T. magnatum. For example, Lalli et al., 2015 [90] found that fruiting bodies of Amanita stenospora Contu, Cortinarius aprinus Melot, Hebeloma quercetorum Quadr. and Hygrophorus arbustivus var. quercetorum Bon & Chevassut were commonly present in T. magnatum productive areas. On the other hand, Mello and colleagues [91] found that the mycelium of Mortierella sp. and Fusarium sp. was more abundant in T. magnatum productive niches than in unproductive ones. Moreover, near the picking point of white truffle ascomata, the fruiting bodies and the ectomycorrhizas of other truffle species were often found together, such as T. rufum and T. maculatum [69,70].
The copresence with T. magnatum of even more Tuber species was shown by examining the soil DNA at the fruiting points using specific primers [7,92]. Whereas the DNA of T. borchii, T. dryophilum, T. rufum, T. maculatum, T. brumale, and T. macrosporum were detected together with that of T. magnatum, the DNA of T. macrosporum and T. aestivum was never amplified, showing different ecological niches and or/competitive exclusion [7].

6. White Truffle Production and Harvesting in Natural Sites

Tuber magnatum is the truffle which has the longest tradition of being harvested by wild truffle hunters. Truffle hunting and extraction in Italy was inscribed in 2021 [93] in the Representative List of the Intangible Cultural Heritage of Humanity by UNESCO. That is a set of knowledge and practices that has been passed down from father to son, generation after generation [13]. The truffle hunters use trained dogs that are able to detect the truffle in the soil thanks to their highly developed sense of smell and use of special spades to extract the truffles without disturbing the soil conditions. Today, white truffle hunting has an important socioeconomic role, especially in the mountainous and hilly marginal areas of the Italian peninsula. In the Italian region of Molise, truffle hunters reach 1.47% of the total population [94]. The mystic of truffle hunting has created a truffle culture and access to a new truffle tourism, where a truffle hunter together with his dog will lead tourists through the woods looking for white truffle [95]. This interest in truffle hunting comes at a time when the rural economies of mountainous areas are struggling with high unemployment and with securing sustainable agricultural income [96].
Truffle hunting is traditionally practiced while respecting the environment and plant biodiversity, ensuring the seasonal regeneration of the truffle. However, white truffle natural production in Italy is endangered by several factors including the truffle hunting pressure in some Italian regions. The number of truffle hunters is constantly increasing, and their official number is now more than 70,000 [94] in Italy. Moreover, climate change and forest abandonment threaten the production of this truffle. Although some forest managements such as soil tillage, irrigation and selective thinning in production areas can help truffle production and T. magnatum mycelium development in the soil [97], they are difficult to realize in the mountainous areas of the Apennines where T. magnatum is widespread [13,98]. More specific studies for the improvement of natural white truffle production areas through the adoption of innovative silvicultural techniques are in progress in Italy [94].

7. Cultivation

Modern truffle cultivation started in the 1970s. It consists of producing mycorrhizal plants in a greenhouse and then out-planting them into areas with suitable soils and climate [13]. Using this technique, T. melanosporum, T. aestivum, T. borchii and other less valuable Tuber spp. are now successfully cultivated not only in Europe but also in countries well outside their natural distribution such as Australia, Chile, Israel, New Zealand, South Africa and the UK [13,17,99].
Because of the price commanded by T. magnatum, it was natural that research towards the end of the 1990s would focus on this species in Italy [100]. However, after a dozen years, the unreliability of production of the first plantations induced a degree of skepticism towards white truffle cultivation [101] and questions were raised whether the right inoculum had been used to begin with. Bullini et al., 1994 [102] then demonstrated, using isoenzymes, that none of the commercial plants that they had tested had been mycorrhized with T. magnatum but with other Tuber species such as T. borchii and T. maculatum. Mello et al., 2001 [16] and Rubini et al., 2001 [19], using a molecular analysis, subsequently showed that the ectomycorrhizal morphology of T. magnatum described in Italy in 1978 was incorrect and most of the plants produced at that time were contaminated with less valuable species of truffle—a consequence of the spore inoculation technique that had been used [13,103]. Plants that had been used to establish truffières sometimes were also contaminated with common greenhouse contaminants such as Sphaerosporella brunnea (Alb. & Schwein.) Svrček & Kubička and Pulvinula convexella (P. Karst.) Pfister [104,105,106]. Fortunately, some T. magnatum cultivation attempts were successful albeit limited to just a few ascomata [107]. Donnini et al., 2000 [107] and Gregori et al., 2008 [101] reported that different T. magnatum orchards established with Tilia spp., Quercus spp., Populus spp., Salix caprea L. and Ostrya carpinifolia Scop. mycorrhized with T. magnatum between 1986 and 1993 and started to produce from 6 to 10 years after planting. In the first years, these orchards produced large whitish ascocarps molecularly identified as T. borchii [17] and only later was T. magnatum [101] produced. The medium annual amount of T. magnatum ascocarps harvested was between a few hectograms and a few kilograms per hectare [101]. Similarly, a small truffière covering 4000 m2 located in Emilia Romagna produced only T. borchii from the 3rd year to the 12th year after planting and then T. magnatum from the 13th year after planting, which completely replaced T. borchii (Figure 2) [108]. This behavior of several Italian T. magnatum truffle grounds could be explained as a species succession from an early-stage fungus (T. borchii) [109] and a later-stage fungus (T. magnatum), which tends to fruit under adult plants. The coexistence of the mycelia of different Tuber species in T. magnatum productive sites is a common feature as previously reported (see Section 5) [7,92]. Probably, these other Tuber spp. do not compete with T. magnatum as thought in the past but share the same ecological niche establishing neutral or even synergistic relationships. However, in these productive first T. magnatum plantations, we cannot exclude that the production was a spontaneous event and not the consequence of planting, at that time, uncertain T. magnatum mycorrhized plants. These plantations were in fact all realized in areas where T. magnatum naturally occurred. A spontaneous mycorrhization often occurs in poplar planted in the fresh, deep calcareous soils along the channels of the Padania plain in Italy. Thus, in order to increase T. magnatum production the member of the local truffle hunting association used to plant poplar cuttings renting the soil from public administration [17].
Nowadays, T. magnatum cultivation has received a new impetus [110]. With the development of specific primers, T. magnatum mycorrhizas and mycelium can now be unequivocally identified [71,98,111] and several nurseries have begun to produce certified T. magnatum mycorrhized plants both in Italy and France [17,112]. However, the prices of these plants are higher than for those inoculated with other species of truffle because of the high cost of the inoculum and the still present difficulties in producing plants well colonized with T. magnatum.
In 2019 and 2020, it was demonstrated in France that it was possible to cultivate T. magnatum just like other species of truffles, and moreover, outside the natural T. magnatum area [112], and only 4.5 years after planting, similar to T. melanosporum and T. aestivum orchards [113,114]. This is particularly exciting, but field studies are still necessary to optimize T. magnatum cultivation practices.

8. Conclusions and Prospects

Tuber magnatum is undoubtedly the most sought-after and valuable of the truffles. Although many studies have been devoted to this species over the past thirty years, numerous aspects of its biology and ecology are still to be unraveled. A Google scholar search covering the past 22 years produced 2440 results from 1990 to today (retrieved on 21 September 2022). Moreover, its peculiar environmental characteristics and its harvesting culture contribute to create an aura of mystery around this truffle and to increase its commercial value.
After numerous failures and uncertain results, T. magnatum cultivation has now been deemed possible inside and outside Italy [112]. It opens up new perspectives to increase its production, which has actually been declining due to several factors including climate changes and overharvesting. Planning actions to protect the white truffle’s natural habitat and to preserve this species and the plantation of experimental plantations are needed. However, an optimization of the management strategies of T. magnatum cultivation is necessary to definitely tame this precious truffle. New molecular tools perfected in the last years (such as qPCR) for the detection and quantification of T. magnatum mycelium in the soil could assist in this indispensable research processes.

Author Contributions

Writing original draft preparation, S.G. and A.Z.; writing-review and editing, A.Z. and I.R.H.; figures, A.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This entry is part of the 37th cycle of the Ph.D. course in “Health, Safety and Green System”, PON call “Research and Innovation” 2014–2020.

Data Availability Statement

Not applicable.

Acknowledgments

We thank Alberto Previati for the data of Figure 2b and Olga Urbani for information on truffle prices.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Morphology of T. magnatum ascomata (ac), spores (bar = 10 µm) (d), mycorrhizas (bar = 100 µm) (e) and mycelium-colored with blue cotton (bar = 10 µm) (fh). (a) T. magnatum broken ascoma, (b) reddish patches, (c) brown spots, (d) reticulated spores, (e) T. magnatum mycorrhizas, (f) hyphal aggregates, (g) vesicles and (h) anastomosis.
Figure 1. Morphology of T. magnatum ascomata (ac), spores (bar = 10 µm) (d), mycorrhizas (bar = 100 µm) (e) and mycelium-colored with blue cotton (bar = 10 µm) (fh). (a) T. magnatum broken ascoma, (b) reddish patches, (c) brown spots, (d) reticulated spores, (e) T. magnatum mycorrhizas, (f) hyphal aggregates, (g) vesicles and (h) anastomosis.
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Figure 2. Old T. magnatum cultivation. (a) T. magnatum orchard of Q. robur mycorrhized plants; (b) ascocarp production trend during the first 20 years after plantation.
Figure 2. Old T. magnatum cultivation. (a) T. magnatum orchard of Q. robur mycorrhized plants; (b) ascocarp production trend during the first 20 years after plantation.
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Graziosi, S.; Hall, I.R.; Zambonelli, A. The Mysteries of the White Truffle: Its Biology, Ecology and Cultivation. Encyclopedia 2022, 2, 1959-1971. https://doi.org/10.3390/encyclopedia2040135

AMA Style

Graziosi S, Hall IR, Zambonelli A. The Mysteries of the White Truffle: Its Biology, Ecology and Cultivation. Encyclopedia. 2022; 2(4):1959-1971. https://doi.org/10.3390/encyclopedia2040135

Chicago/Turabian Style

Graziosi, Simone, Ian Robert Hall, and Alessandra Zambonelli. 2022. "The Mysteries of the White Truffle: Its Biology, Ecology and Cultivation" Encyclopedia 2, no. 4: 1959-1971. https://doi.org/10.3390/encyclopedia2040135

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