Tuber melanosporum

Tuber melanosporum, called the black truffle, Périgord truffle or French black truffle,[1] is a species of truffle native to Southern Europe. It is one of the most expensive edible mushrooms in the world.

Tuber melanosporum
Fruiting body of Tuber melanosporum
Scientific classification
Kingdom:	Fungi
Division:	Ascomycota
Class:	Pezizomycetes
Order:	Pezizales
Family:	Tuberaceae
Genus:	Tuber
Species:	T. melanosporum
Binomial name
Tuber melanosporum Vittad. 1831

Tuber melanosporum
float Mycological characteristics
	glebal hymenium
	hymenium attachment is not applicable
	lacks a stipe
	ecology is mycorrhizal
	edibility: choice

Taxonomy

Italian naturalist Carlo Vittadini described the black truffle in 1831.

Description

External characteristics

The round, dark brown fruiting bodies (ascocarps) have a black-brown skin with small pyramidal cusps.[2] They have a strong, aromatic smell and normally reach a size of up to 10 cm (3.9 in).[3] Some may be significantly larger, such as a black truffle found 2012 in Dordogne with a mass of 1.277 kg (2.82 lb).[4]

Their flesh is initially white, then dark. It is permeated by white veins which turn brown with age.[5] The spores are elliptical and measure about 22–55 µm by 20–35 µm.[3] They are dark brown and covered with large spikes.

Aroma

The fruiting bodies of the black truffle exude a scent reminiscent of undergrowth, strawberries, wet earth or dried fruit with a hint of cocoa. Their taste, which fully develops after the truffles are heated, is slightly peppery and bitter.[6] If stored at room temperature, the aromatic compounds dissipate, while storage around the freezing point (0°C) leads to an increased synthesis of these compounds.

The volatile compounds that contribute to the aroma and are developed by the fruiting bodies include 2-methyl-1-butanol, isoamyl alcohol, 2-methylbutyraldehyde and 3-methylbutyraldehyde, as well as traces of sulfur compounds.[6][7] One of these, dimethyl sulfide, is what attracts truffle dogs, truffle hogs and truffle flies to the fruiting bodies.[8] Several species of yeast, which produce part of the aromatic compounds, have been isolated from Tuber melanosporum and Tuber magnatum.[9]

Genome

The genome of the black truffle was published in 2010.[10] It contains 125 million base pairs, 58% of the genome consists of transposable elements, and the genome contains only 7500 identified protein-encoding genes. During symbiosis, genes involved in the decomposition of plant cell walls and lipids are induced. This indicates that black truffles decompose the cell walls of their host plants at the beginning of the symbiosis.

Identification

Black truffle, cut

The black truffle is morphologically very similar to the commercially less valuable Chinese truffle (Tuber indicum). To avoid fraud or misidentifications in commerce, a RFLP genetic test has been developed to distinguish the two species.[11] Externally, they can be distinguished by their skin, which is smoother and dark red or dark brown in the Chinese truffle. Two other similar truffle species are the summer truffle (Tuber aestivum) and the winter truffle (Tuber brumale), whose flesh is of a lighter color.

Ecology

Development and phenology

Black truffles suppress the growth of plants around their symbiont, creating the impression of a burnt area.

Black truffles grow at a depth of 5 cm (2.0 in) to 50 cm (20 in) as ectomycorrhizae, preferably in loose calcareous soil,[12] close to the roots of their plant symbionts. These include holm oaks, French oaks, hazel, cherry and other deciduous trees.[3] The symbiosis of holm oak saplings and black truffles has been shown to improve photosynthesis and root growth in the plant.[13]

Black truffles suppress the growth of plants around their symbiont, creating the impression of a burnt (brûlé) area around it. They do so by parasitizing the roots of other plants, which may lead to necrosis of the root bark and the death of the parasitized plant.[14] Moreover, part of the scent emitted by the truffles may limit the growth of other plants through oxidative stress.[15]

In the Northern Hemisphere, the fruiting bodies develop from April to June, and are harvested from November to March.[16]

Reproduction

Boars and the larvae of the truffle fly (Suillia tuberiperda), which eat the fruiting bodies, aid in the distribution of the species by excreting the indigestible spores. Their excrement likely also serves to fertilize the spores. Black truffles are sometimes found together with winter truffles, which aid the growth of black truffles in wet soils.[17]

Until 2010, all truffle species were thought to be homothallic, that is, capable of sexual reproduction from a single organism. Subsequent research indicated that black truffles are heterothallic, that is, sexual reproduction requires contact between the mycelia of different mating types.[18] If a tree is surrounded by mycelia of different mating types, eventually one type becomes predominant. This is relevant for the operation of truffle plantations: To improve production, planters must ensure that neighboring trees harbor mycelia of different mating types, such as by inoculating new saplings with a mycelium of a particular type.

Habitat and cultivation

The natural habitat of the black truffle includes various regions in Spain, France, and Italy. These are presumably the areas where the host plants found refuge during the last Ice Age. In these areas, the search for black truffles and their cultivation is a tradition going back more than 200 years. Truffles are still collected manually in a traditional way in large areas of natural forests. For example, the county of Alto Maestrazgo (province of Castellón, Spain) has an ideal ground with suitable conditions for cultivating truffles. Albocàsser, Atzaneta, Culla, or Morella are just some of the villages in this region where one can find black truffles in large amounts.[19]

Nevertheless, this form of recollection is increasingly affected by climate change and since 2010, a significant drop in productivity has occurred in naturally producing forests. In exchange, cultivated areas are increasingly popular, and in central Spain, several thousands of hectares are dedicated to truffle cultivation (the Mecca of the black truffle being in Soria, Teruel province in the Aragon region). Some experiments have also been conducted in burnt areas, with promising results, as legally no need to ask for a land-use change exists when planting truffles, as it can be considered (EU-28) as forest land.[20]

Black truffles are now also cultivated in Australia, New Zealand, Chile,[21] North America, South Africa,[12][22] and Wales.[23] Cultivation involves the planting of, for example, hazel trees whose roots are inoculated with truffle mycelium. The first fruiting bodies can be harvested about 4-10 years after planting the trees.[24]

Production

France accounts for some 45% of the world production of black truffles, Spain for 35% and Italy for 20%. Smaller amounts are produced in Slovenia, Croatia, and the Australian states of Tasmania and Western Australia. In 2005, black truffles were found in Serbia.[25] About 80% of the French production comes from southeast France: upper Provence (départements of Vaucluse and Alpes-de-Haute-Provence), part of Dauphiné (département of Drôme), and part of Languedoc (département of Gard). About 20% of the production comes from southwest France: Quercy (département of Lot) and Périgord. The largest truffle market in France (and probably also in the world) is at Richerenches in Vaucluse. The largest truffle market in southwest France is at Lalbenque in Quercy. These markets are busiest in January, when the black truffles have their highest perfume.

Production has considerably diminished during the 20th century, dropping to around 20 metric tonnes per year, with peaks around 46 tonnes in the best years. By comparison, in 1937, France produced around 1,000 metric tonnes of black truffles.

The following table shows the production in the EU of T. melanosporum in Spain, France, and Italy. Production data are in metric tons, and country weights in percentage, and come from the Groupe Européen Truffe et Trufficulture, an association of the main producers in Europe.

Years	Spain	France	Italy	EU	% of average year	Spain vs EU	France vs EU	Italy vs EU
1990/1991	30	17	5	52	83	58	33	10
1991/1992	10	20	5	35	56	29	57	14
1992/1993	23	31	3	57	90	40	54	5
1993/1994	9	22	2	33	52	27	67	6
1994/1995	4	12	30	46	73	9	26	65
1995/1996	20	19	25	64	102	31	30	39
1996/1997	25	50	20	95	151	26	53	21
1997/1998	80	30	24	134	213	60	22	18
1998/1999	7	14	4	25	40	28	56	16
1999/2000	35	40	10	85	135	41	47	12
2000/2001	6	35	4	45	71	13	78	9
2001/2002	20	15	5	40	63	50	38	13
2002/2003	40	35	20	95	151	42	37	21
2003/2004	7	9	6	22	35	32	41	27
2004/2005	22	27	10	59	94	37	46	17
2005/2006	14	15	8	37	59	38	41	22
2006/2007	20	28	10	58	92	34	48	17
2007/2008	25	26	8	59	94	42	44	14
2008/2009	14	58	20	92	146	15	63	22
2009/2010	9	32	8	49	78	18	65	16
2010/2011	18	37,2	12	67,2	107	27	55	18
2011/2012	14,5	42,3	8	64,8	103	22	65	12
2012/2013	15	38,2	20	73,2	116	20	52	27
2013/2014	45	50	30	125	198	36	40	24

As the data show, France has been the main producer of black truffles in the last decade and a half, but is rapidly challenged by Spain, where regions have made use of the EU-funded Rural Development Programme to subsidise cultivated plantations.[26] This is particularly visible in the Teruel province of the Aragón region, where the black truffle represents the first and main economic activity (in GDP and employment), especially since 2010-2011 when many plantations opened under the last Rural Development Programme 2000-2006 came into production phase.[27]

Commerce and use

With a price of about 1,000 to 2,000 euros per kilogram, black truffles are the second-most expensive truffles after white truffles, and one of the most sought-after edible mushrooms in the world.[16]

In cooking, black truffles are used to refine the taste of meat, fish, soups, and risotto. Unlike white truffles, the aroma of black truffles does not diminish when they are heated, but becomes more intense.[28]

In Spain, where black truffles are often used in cooking, one truffle dish is known as blanched eggs, or huevos escaldados in Spanish.[19]

Physiology

Truffles contain the endocannabinoid anandamide (AEA) and the major metabolic enzymes of the endocannabinoid system (ECS). The AEA content increases in the late stages of truffles’ development. AEA and ECS metabolic enzymes may have evolved earlier than endocannabinoid-binding receptors, and AEA might be an ancient attractant to truffle-eating animals, which are well-equipped with endocannabinoid-binding receptors.[29]

See also

• Media related to Tuber melanosporum at Wikimedia Commons
• List of Tuber species
• Forest Sciences Centre of Catalonia (CTFC) - Non-timber products department

References

1. There are several common names for the species in the popular literature. For example, the Field Guide to North American Truffles (Trappe, Evans & Trappe, 2007) refers to it as the "French black"; Taming the Truffle (Hall, Brown, Zambonelli, 2007) calls it the "black Périgord truffle" (but lists it under the scientific name in the index); The Book of Fungi (Roberts & Evans, 2011) calls it the "black truffle"; and the European field guide Mushrooms (Laessoe & Lincoff, 2002) calls it simply the "Perigord truffle".
2. Gerhardt, Ewald (2011). Der große BLV-Pilzführer für unterwegs. Munich. p. 662. ISBN 978-3-8354-0644-5.
3. Laux, Hans E. (2010). Der große Kosmos-Pilzführer. Alle Speisepilze mit ihren giftigen Doppelgängern. Stuttgart: Kosmos. p. 688. ISBN 978-3-440-12408-6.
4. "1,3 Kilo schwerer Trüffel in Dordogne gefunden". ORF. 15 January 2012. Retrieved 27 July 2013.
5. Cetto, Bruno (1988). Täublinge, Milchlinge, Boviste, Morcheln, Becherlinge u.a. Enzyklopädie der Pilze. 4. Munich: BLV. p. 477. ISBN 978-3-405-13477-8.
6. Franco Bellesia; Adriano Pinetti; Alberto Bianchi; Bruno Tirillini (1998), "The volatile organic compounds of black truffle (Tuber melanosporum Vitt.) from Middle Italy", Flavour and Fragrance Journal (in German), 13 (1), pp. 56–58, doi:10.1002/(SICI)1099-1026(199801/02)13:1<56::AID-FFJ692>3.0.CO;2-X
7. Laura Culleré; Vicente Ferreira; Berenger Chevret; María E. Venturini; Ana C. Sánchez-Gimeno; Domingo Blanco (2010), "Characterisation of aroma active compounds in black truffles (Tuber melanosporum) and summer truffles (Tuber aestivum) by gas chromatography–olfactometry", Food Chemistry (in German), 122 (1), pp. 300–306, doi:10.1016/j.foodchem.2010.02.024
8. T. Talou; A. Gaset; M. Delmas; M. Kulifaj; C. Montant (1990), "Dimethyl sulphide: the secret for black truffle hunting by animals?", Mycological Research (in German), 94 (2), pp. 277–278, doi:10.1016/S0953-7562(09)80630-8
9. Pietro Buzzini u. a. (2005), "Production of volatile organic compounds (VOCs) by yeasts isolated from the ascocarps of black (Tuber melanosporum Vitt.) and white (Tuber magnatum Pico) truffles", Archives of Microbiology (in German), 184 (3), pp. 187–193, doi:10.1007/s00203-005-0043-y, PMID 16187098
10. Francis Martin u. a. (2010), "Périgord black truffle genome uncovers evolutionary origins and mechanisms of symbiosis", Nature (in German), 464 (7291), pp. 1033–1038, doi:10.1038/nature08867, PMID 20348908
11. Francesco Paolocci; Andrea Rubini; Bruno Granetti; Sergio Arcioni (1997), "Typing Tuber melanosporum and Chinese black truffle species by molecular markers", FEMS Microbiology Letters (in German), 153 (2), pp. 255–260, doi:10.1111/j.1574-6968.1997.tb12582.x, PMID 9271850
12. C. C. Linde; H. Selmes (2012), "Genetic Diversity and Mating Type Distribution of Tuber melanosporum and Their Significance to Truffle Cultivation in Artificially Planted Truffiéres in Australia", Applied and Environmental Microbiology (in German), 78 (18), pp. 6534–6539, doi:10.1128/AEM.01558-12, PMC 3426713, PMID 22773652
13. Andrea Nardinia; Sebastiano Salleo; Melvin T. Tyree; Moreno Vertovec (2000), "Influence of the ectomycorrhizas formed by Tuber melanosporum Vitt. on hydraulic conductance and water relations of Quercus ilex L. seedlings" (PDF), Annals of Forest Science (in German), 57 (4), pp. 305–312, doi:10.1051/forest:2000121
14. I. Plattner; I.R. Hall (1995), "Parasitism of non-host plants by the mycorrhizal fungus Tuber melanosporum", Mycological Research (in German), 99 (11), pp. 1367–1370, doi:10.1016/S0953-7562(09)81223-9
15. Richard Splivallo; Mara Novero; Cinzia M Bertea; Simone Bossi; Paola Bonfante (2007), "Truffle volatiles inhibit growth and induce an oxidative burst in Arabidopsis thaliana", The New Phytologist (in German), 175 (3), pp. 417–424, doi:10.1111/j.1469-8137.2007.02141.x, PMID 17635217
16. "Schwarze Trüffel". Huettenhilfe.de. Retrieved 27 July 2013.
17. M. Mamoun; J. M. Olivier (1993), "Competition between Tuber melanosporum and other ectomycorrhizal fungi under two irrigation regimes", Plant and Soil (in German), 149 (2), pp. 211–218, doi:10.1007/BF00016611
18. Andrea Rubini; Beatrice Belfiori; Claudia Riccioni; Sergio Arcioni; Francis Martin; Francesco Paolocci (2011), "Tuber melanosporum: mating type distribution in a natural plantation and dynamics of strains of different mating types on the roots of nursery-inoculated host plants", New Phytologist (in German), 189 (3), pp. 723–735, doi:10.1111/j.1469-8137.2010.03493.x, PMID 20964691
19. "Spanish Truffle Recipes: Slow Food and the Truffle Season in Spain". Slow Living Mediterráneo. 9 February 2017. Retrieved 13 June 2017.
20. Martinez de aragon, Juan; Fischer, Christine; Bonet, Jose-Antonio; olivera, Antoni; Oliach, Daniel; Colinas, Carlos (2012). "Economically profitable post fire restoration with black truffle (Tuber melanosporum) producing plantations". New Forests. 43 (5–6): 615–630. doi:10.1007/s11056-012-9316-x.
21. "Archived copy". Archived from the original on 5 January 2015. Retrieved 4 January 2015.CS1 maint: archived copy as title (link)
22. http://www.news24.com/SouthAfrica/News/kokstad-farmer-finds-first-black-truffle-of-season-20160614
23. https://www.int-res.com/abstracts/cr/v74/n1/p67-70/
24. madrimasd. "New technique to grow black truffles." ScienceDaily, 23 Oct. 2012. Web. 5 Aug. 2013.
25. "KURIR". Arhiva.kurir-info.rs. Retrieved 16 June 2012.
26. Bonet, Jose-Antonio; Fischer, Christine; Colinas, Carlos (2006). "Cultivation of black truffle to promote reforestation and land-use stability". Agronomy for Sustainable Development. 26 (1): 69–76. doi:10.1051/agro:2005059.
27. Bonet, Jose-Antonio; Oliach, Daniel; Fischer, Christine; Martinez de Aragon, Juan; Colinas, Carlos (2009). "Cultivation Methods of the Black Truffle, the Most Profitable Mediterranean Non-Wood Forest Product; A State of the Art Review". Modelling, Valuing and Managing Mediterranean Forest Ecosystems for Non-Timber Goods and Services (57): 57–71.
28. Jochim, Tobias. "Trüffel". Gourmetglobe.de. Retrieved 27 July 2013.
29. Pacioni, Giovanni; Rapino, Cinzia; Zarivi, Osvaldo; Falconi, Anastasia; Leonardi, Marco; Battista, Natalia; Colafarina, Sabrina; Sergi, Manuel; Bonfigli, Antonella (1 February 2015). "Truffles contain endocannabinoid metabolic enzymes and anandamide". Phytochemistry. 110: 104–110. doi:10.1016/j.phytochem.2014.11.012. PMID 25433633.