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A truffle is the fruiting body of a subterranean
ascomycete Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defi ...
fungus, predominantly one of the many species of the genus '' Tuber''. In addition to ''Tuber'', many other genera of fungi are classified as truffles including '' Geopora'', '' Peziza'', ''
Choiromyces ''Choiromyces'' is a genus of truffle-like fungi in the Tuberaceae The Tuberaceae () are a family of mycorrhizal fungi in the order Pezizales, that evolved during or after the first major radiation of Angiosperms in the Jurassic period (140 ...
'', '' Leucangium'', and over a hundred others. These genera belong to the class
Pezizomycetes Pezizomycetes are a class of fungi within the division Ascomycota. Pezizomycetes are apothecial fungi, meaning that their spore-producing/releasing bodies (ascoma) are typically disk-like, bearing on their upper surfaces a layer of cylindrical s ...
and the
Pezizales The Pezizales are an order of the subphylum Pezizomycotina within the phylum Ascomycota. The order contains 16 families, 199 genera, and 1683 species. It contains a number of species of economic importance, such as morels, the black and white tr ...
order. Several truffle-like basidiomycetes are excluded from Pezizales, including ''
Rhizopogon ''Rhizopogon'' is a genus of ectomycorrhizal basidiomycetes in the family Rhizopogonaceae. Species form hypogeous sporocarps commonly referred to as "false truffles". The general morphological characters of ''Rhizopogon'' sporocarps are a simpl ...
'' and ''Glomus''. Truffles are
ectomycorrhiza An ectomycorrhiza (from Greek ἐκτός ', "outside", μύκης ', "fungus", and ῥίζα ', "root"; pl. ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobi ...
l fungi, so they are usually found in close association with tree roots. Spore dispersal is accomplished through fungivores, animals that eat fungi. These fungi have significant ecological roles in nutrient cycling and drought tolerance. Some truffle species are highly prized as food. French
gastronome Gastronomy is the study of the relationship between food and culture, the art of preparing and serving rich or delicate and appetizing food, the cooking styles of particular regions, and the science of good eating. One who is well versed in gastr ...
Jean Anthelme Brillat-Savarin called truffles "the diamond of the kitchen". Edible truffles are used in Italian,
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
and numerous other national . Truffles are cultivated and harvested from natural environments.


History


Antiquity

The first mention of truffles appears in the inscriptions of the neo-Sumerians regarding their Amorite enemy's eating habits ( Third Dynasty of Ur, 20th century BCE) and later in writings of Theophrastus in the 4th century BCE. In classical times, their origins were a mystery that challenged many; Plutarch and others thought them to be the result of lightning, warmth, and water in the soil, while Juvenal thought thunder and rain to be instrumental in their origin. Cicero deemed them children of the earth, while Dioscorides thought they were tuberous roots. Rome and Thracia in the Classical period identified three kinds of truffles: '' Tuber melanosporum'', '' T. magnificus'', and '' T. magnatum''. The Romans instead used a variety of fungus called terfez, also sometimes called a "desert truffle". Terfez used in Rome came from Lesbos, Carthage, and especially Libya, where the coastal climate was less dry in ancient times. Their substance is pale, tinged with rose. Unlike truffles, terfez have little inherent flavour. The Romans used the terfez as a flavour carrier because the terfez tends to absorb surrounding flavours. Because Ancient Roman cuisine used many spices and flavourings, the terfez may have been appropriate in that context.


Middle Ages

Truffles were rarely used during the Middle Ages. Truffle hunting is mentioned by
Bartolomeo Platina Bartolomeo Sacchi (; 1421 – 21 September 1481), known as Platina (in Italian ''il Platina'' ) after his birthplace (Piadena), and commonly referred to in English as Bartolomeo Platina, was an Italian Renaissance humanist writer and gastro ...
, the papal historian, in 1481, when he recorded that the sows of Notza were without equal in hunting truffles, but they should be muzzled to prevent them from eating the prize.


Renaissance and modernity

During the Renaissance, truffles regained popularity in Europe and were honoured at the court of King Francis I of France. They were popular in Parisian markets in the 1780s, imported seasonally from truffle grounds, where peasants had long enjoyed them.
Brillat-Savarin Jean Anthelme Brillat-Savarin (; 1 April 1755, Belley, Ain – 2 February 1826, Paris) was a French lawyer and politician, who, as the author of ''The Physiology of Taste'' (''Physiologie du Goût''), gained fame as an epicure and gastronome: " ...
(1825) noted that they were so expensive they appeared only at the dinner tables of great nobles and kept women. They were sometimes served with turkey.


Cultivation

Truffles long eluded techniques of domestication, as
Jean-Anthelme Brillat-Savarin Jean Anthelme Brillat-Savarin (; 1 April 1755, Belley, Ain – 2 February 1826, Paris) was a French lawyer and politician, who, as the author of ''The Physiology of Taste'' (''Physiologie du Goût''), gained fame as an epicure and gastronome: " ...
(1825) noted:
The most learned men have sought to ascertain the secret and fancied they discovered the seed. Their promises, however, were vain, and no planting was ever followed by a harvest. This perhaps is all right, for as one of the great values of truffles is their dearness, perhaps they would be less highly esteemed if they were cheaper.English translation
Truffles can be cultivated. As early as 1808, attempts to cultivate truffles, known in French as , were successful. People had long observed that truffles were growing among the roots of certain trees, and in 1808,
Joseph Talon Joseph is a common male given name, derived from the Hebrew Yosef (יוֹסֵף). "Joseph" is used, along with "Josef", mostly in English, French and partially German languages. This spelling is also found as a variant in the languages of the mo ...
, from
Apt Apt. is an abbreviation for apartment. Apt may also refer to: Places * Apt Cathedral, a former cathedral, and national monument of France, in the town of Apt in Provence * Apt, Vaucluse, a commune of the Vaucluse département of France * A ...
( of Vaucluse) in southern France, had the idea of transplanting some seedlings that he had collected at the foot of oak trees known to host truffles in their root system. For discovering how to cultivate truffles, some sources now give priority to Pierre II Mauléon (1744–1831) of
Loudun Loudun (; ; Poitevin dialect, Poitevin: ''Loudin'') is a Communes of France, commune in the Vienne Departments of France, department and the Regions of France, region of Nouvelle-Aquitaine, western France. It is located south of the town of Chin ...
(in western France), who began to cultivate truffles around 1790. Mauléon saw an "obvious symbiosis" between the oak tree, the rocky soil, and the truffle and attempted to reproduce such an environment by taking acorns from trees known to have produced truffles and sowing them in chalky soil. His experiment was successful, with truffles found in the soil around the newly grown oak trees years later. In 1847, Auguste Rousseau of Carpentras (in Vaucluse) planted of oak trees (again from acorns found on the soil around truffle-producing oak trees), and he subsequently obtained large harvests of truffles. He received a prize at the 1855 World's Fair in Paris. Others imitated these successful attempts in France and Italy. In the late 19th century, an epidemic of
phylloxera Grape phylloxera is an insect pest of commercial grapevines worldwide, originally native to eastern North America. Grape phylloxera (''Daktulosphaira vitifoliae'' (Fitch 1855) belong to the family Phylloxeridae, within the order Hemiptera, bugs ...
destroyed many of the vineyards in southern France. Another epidemic killed most of the
silkworm The domestic silk moth (''Bombyx mori''), is an insect from the moth family Bombycidae. It is the closest relative of ''Bombyx mandarina'', the wild silk moth. The silkworm is the larva or caterpillar of a silk moth. It is an economically imp ...
s there, too, making the fields of
mulberry ''Morus'', a genus of flowering plants in the family Moraceae, consists of diverse species of deciduous trees commonly known as mulberries, growing wild and under cultivation in many temperate world regions. Generally, the genus has 64 identif ...
trees useless. Trufficulture became an important source of income for those affected. The calcareous and exposed vineyard soils were well-suited to the cultivation of truffles. By 1890, truffières (truffle plantations) covered 750 km2 of land in France, and 2,000 tonnes of truffles were produced in that year. From the 19th century to the present, truffle production fell by 97–99% to 20–50 tonnes annually. Reasons given for this decline include the Industrial Revolution, the subsequent
rural flight Rural flight (or rural exodus) is the migratory pattern of peoples from rural areas into urban areas. It is urbanization seen from the rural perspective. In industrializing economies like Britain in the eighteenth century or East Asia in the ...
and the multiple European wars of the 20th century, which reduced the rural population. For example, World War I resulted in the mobilisation of 65% of the agricultural workers from the region of
Lot Lot or LOT or The Lot or ''similar'' may refer to: Common meanings Areas * Land lot, an area of land * Parking lot, for automobiles *Backlot, in movie production Sets of items *Lot number, in batch production *Lot, a set of goods for sale togethe ...
alone. Knowledge of truffle cultivation, the soil and the seasons was lost along with the people. Another consequence was no more grazing sheep or shepherds who pruned trees for feed and fuelwood, so former truffle plantations turned into closed forests that no longer produced truffles. Truffles were once sold at weekly markets (bi-weekly in the case of a market in Martel, Lot) and in quantities of two to six tonnes in good weeks, but only Lalbenque and Limogne today have weekly truffle markets. Prices have increased so that truffles, once seen as a food of the middle class, have become a luxury. The situation changed in the late 1960s and early 1970s, with researchers in France and Italy establishing mycorrhizas with truffle spores. Beginning from the 1980s, truffle plantations are compensating for some of the decline in wild truffles, and exist in various countries including France, Italy, Spain and Australia. About 80% of the truffles now produced in France come from specially planted truffle groves. Investments in cultivated plantations are underway in many parts of the world using controlled irrigation for regular and resilient production. A critical phase of the cultivation is the quality control of the mycorrhizal plants. Between 7 and 10 years are needed for the truffles to develop their mycorrhizal network, and only after that do the host plants come into production. Complete soil analysis to avoid contamination by other dominant fungi and very strict control of the formation of mycorrhizae are necessary to ensure the success of a plantation. Total investment per hectare for an irrigated and barrier-sealed plantation (against wild boars) can cost up to €10,000. Considering the level of initial investment and the maturity delay, farmers who have not taken care of both soil conditions and seedling conditions are at high risk of failure.


New Zealand and Australia

The first black truffles ('' Tuber melanosporum'') to be produced in the Southern Hemisphere were harvested in Gisborne, New Zealand in 1993. New Zealand's first burgundy truffle was found in July 2012 at a Waipara truffle farm. It weighed 330 g and was found by the farm owner's beagle. In 1999, the first Australian truffles were harvested in Tasmania, the result of eight years of work. Trees were inoculated with the truffle fungus to create a local truffle industry. Their success and the value of the resulting truffles has encouraged a small industry to develop. Truffle production has expanded into the colder regions of Victoria, New South Wales and Western Australia. In 2014, over of truffles were harvested by Truffle Hill, Manjimup, Western Australia. In June 2014, A grower harvested Australia's largest truffle from their property at Robertson, in the Southern Highlands of New South Wales. It was a French black perigord fungus weighing in at and was valued at over $2,000 per kilogram.


United States

Périgord truffles were first farmed in Tennessee in 2007. At its peak in the 2008–2009 season, one farm produced about 200 pounds of truffles, but Eastern filbert blight almost entirely wiped out the hazel trees by 2013 and production dropped, essentially ending the business. Eastern filbert blight similarly destroyed the orchards of other once-promising commercial farms in East Tennessee, while newer farms in California, North Carolina, Oregon, and Arkansas were started. , the Appalachian truffle (''Tuber canaliculatum'') was being developed as a potential market.


Etymology

The origin of the word "truffle" is from the Tamazight language in North Africa, where the truffle is native to the
Atlas Mountains The Atlas Mountains are a mountain range in the Maghreb in North Africa. It separates the Sahara Desert from the Mediterranean Sea and the Atlantic Ocean; the name "Atlantic" is derived from the mountain range. It stretches around through Moroc ...
. In Moroccan Tamazight, the "truffle" is called ''tireffas'', which comes from the verb ''youfess'', meaning "to bury," referring to how deeply rooted truffles are under the soil. Other sources also attribute "truffle" to originate from the Latin term , meaning "swelling" or "lump", which became ''tufer.'' However, the Tamazight term predates the Latin term, and is phonologically closer to the various European terms used today: Danish , Dutch , English truffle, French , German , Greek τρούφα ''trúfa'', Italian , Polish , Romanian , Spanish , and Swedish . Additionally, in Moroccan Arabic, the term used is ''tirfa'' (ترفة). The German word ("potato") is derived from the Italian term for truffle because of superficial similarities. In Portuguese, the words and are synonyms, the latter closer to the Latin term.


Phylogeny

Phylogenetic analysis has demonstrated the convergent evolution of the ectomycorrhizal trophic mode in diverse fungi. The subphylum, Pezizomycotina, containing the order Pezizales, is approximately 400 million years old. Within the order Pezizales, subterranean fungi evolved independently at least fifteen times. Contained within Pezizales are the families
Tuberaceae The Tuberaceae () are a family of mycorrhizal fungi in the order Pezizales, that evolved during or after the first major radiation of Angiosperms in the Jurassic period (140–180 million years ago, Mya). It includes the genus ''Tuber'', which ...
,
Pezizaceae The Pezizaceae (commonly referred to as cup fungi) are a family of fungi in the Ascomycota which produce mushrooms that tend to grow in the shape of a "cup". Spores are formed on the inner surface of the fruit body (mushroom). The cup shape typ ...
, Pyronematacae, and
Morchellaceae The Morchellaceae are a family of ascomycete fungi in the order Pezizales. According to a standard reference work, the family has contained at least 49 species distributed among four genera. However, in 2012, five genera that produce ascoma that ...
. All of these families contain lineages of subterranean or truffle fungi. The oldest ectomycorrhizal fossil is from the Eocene about 50 million years ago. This indicates that the soft bodies of ectomycorrhizal fungi do not easily fossilise. Molecular clockwork has suggested the evolution of ectomycorrhizal fungi occurred approximately 130 million years ago. The evolution of subterranean fruiting bodies has arisen numerous times within the
Ascomycota Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...
,
Basidiomycota Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basi ...
, and
Glomeromycota Glomeromycota (often referred to as glomeromycetes, as they include only one class, Glomeromycetes) are one of eight currently recognized divisions within the kingdom Fungi, with approximately 230 described species. Members of the Glomeromycot ...
. For example, the genera ''
Rhizopogon ''Rhizopogon'' is a genus of ectomycorrhizal basidiomycetes in the family Rhizopogonaceae. Species form hypogeous sporocarps commonly referred to as "false truffles". The general morphological characters of ''Rhizopogon'' sporocarps are a simpl ...
'' and '' Hysterangium'' of Basidiomycota both form subterranean fruiting bodies and play similar ecological roles as truffle forming ascomycetes. The ancestors of the Ascomycota genera ''Geopora'', ''Tuber'', and ''Leucangium'' originated in Laurasia during the Paleozoic era. Phylogenetic evidence suggests that most subterranean fruiting bodies evolved from above-ground mushrooms. Over time mushroom stipes and caps were reduced, and caps began to enclose reproductive tissue. The dispersal of sexual spores then shifted from wind and rain to utilising animals. The phylogeny and
biogeography Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, ...
of the genus ''Tuber'' was investigated in 2008 using internal transcribed spacers (ITS) of nuclear DNA and revealed five major
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
s (Aestivum, Excavatum, Rufum, Melanosporum and Puberulum); this was later improved and expanded in 2010 to nine major clades using large subunits (LSU) of
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
. The Magnatum and Macrosporum clades were distinguished as distinct from the Aestivum clade. The Gibbosum clade was resolved as distinct from all other clades, and the Spinoreticulatum clade was separated from the Rufum clade. The truffle habit has evolved independently among several basidiomycete genera. Phylogenetic analysis has revealed that basidiomycete subterranean fruiting bodies, like their ascomycete counterparts, evolved from above ground mushrooms. For example, ''Rhizopogon'' species likely arose from an ancestor shared with '' Suillus'', a mushroom-forming genus. Studies have suggested that selection for subterranean fruiting bodies among ascomycetes and basidiomycetes occurred in water-limited environments.


Species


Black

The black truffle or black Périgord truffle (''Tuber melanosporum''), the second-most commercially valuable species, is named after the Périgord region in France. Black truffles associate with oaks,
hazel The hazel (''Corylus'') is a genus of deciduous trees and large shrubs native to the temperate Northern Hemisphere. The genus is usually placed in the birch family Betulaceae,Germplasmgobills Information Network''Corylus''Rushforth, K. (1999). ...
nut, cherry, and other deciduous trees and are harvested in late autumn and winter. The genome sequence of the black truffle was published in March 2010.


Summer or burgundy

The black summer truffle (''Tuber aestivum'') is found across Europe and is prized for its culinary value. Burgundy truffles (designated '' Tuber uncinatum'', but the same species) are harvested in autumn until December and have aromatic flesh of a darker colour. These are associated with various trees and shrubs.


White

Tuber magnatum, the high-value ''white truffle'' (''tartufo bianco d'Alba'' in Italian) is found mainly in the
Langhe The Langhe (; ''Langa'' is from old dialect Mons Langa et Bassa Langa) is a hilly area to the south and east of the river Tanaro in the province of Cuneo and in the province of Asti in Piedmont, northern Italy. It is famous for its wines, chees ...
and Montferrat areas of the Piedmont region in northern Italy, and most famously, in the countryside around the cities of Alba and
Asti Asti ( , , ; pms, Ast ) is a ''comune'' of 74,348 inhabitants (1-1-2021) located in the Piedmont region of northwestern Italy, about east of Turin in the plain of the Tanaro River. It is the capital of the province of Asti and it is deemed t ...
. A large percentage of Italy's white truffles also come from Molise.


Whitish

The " whitish truffle" (''Tuber borchii'') is a similar species native to Tuscany,
Abruzzo Abruzzo (, , ; nap, label=Neapolitan language, Abruzzese Neapolitan, Abbrùzze , ''Abbrìzze'' or ''Abbrèzze'' ; nap, label=Sabino dialect, Aquilano, Abbrùzzu; #History, historically Abruzzi) is a Regions of Italy, region of Southern Italy wi ...
,
Romagna Romagna ( rgn, Rumâgna) is an Italian historical region that approximately corresponds to the south-eastern portion of present-day Emilia-Romagna, North Italy. Traditionally, it is limited by the Apennines to the south-west, the Adriatic to t ...
, Umbria, the
Marche Marche ( , ) is one of the twenty regions of Italy. In English, the region is sometimes referred to as The Marches ( ). The region is located in the central area of the country, bordered by Emilia-Romagna and the republic of San Marino to the ...
, and Molise. It is reportedly not as aromatic as those from Piedmont, although those from Città di Castello are said to come quite close.


Other ''Tuber''

A less common truffle is "garlic truffle" (''
Tuber macrosporum ''Tuber macrosporum'', commonly known as the smooth black truffle, is a species of edible truffle in the family Tuberaceae. Found in Europe, and common in central Italy, the truffle was described as new to science by Italian mycologist Carlo Vi ...
''). In the U.S. Pacific Northwest, several species of truffle are harvested both recreationally and commercially, most notably, the '' Leucangium carthusianum'', Oregon black truffle; ''
Tuber gibbosum ''Tuber gibbosum'' is a species of truffle in the genus ''Tuber''. It is found in the Pacific Northwest region of the United States, where it grows in an ectomycorrhizal association with Douglas-fir. It is commercially collected between as ea ...
'', Oregon spring white truffle; and ''
Tuber oregonense ''Tuber oregonense'', commonly known as the Oregon white truffle, is a species of edible truffle in the genus ''Tuber''. Described as new to science in 2010, the North American species is found on the western coast of the United States, from ...
'', the Oregon winter white truffle. '' Kalapuya brunnea'', the Oregon brown truffle, has also been commercially harvested and is of culinary note. The pecan truffle (''Tuber lyonii'') syn. ''texense'' is found in the Southern United States, usually associated with pecan trees. Chefs who have experimented with them agree "they are very good and have potential as a food commodity". Although pecan farmers used to find them along with pecans and discard them, considering them a nuisance, they sell for about $160 a pound and have been used in some gourmet restaurants.


Beyond ''Tuber''

The term "truffle" has been applied to several other genera of similar underground fungi. The genera ''
Terfezia ''Terfezia'' (Berber: Tirfas) is a genus of truffle-like fungi within the Pezizaceae family. ''Terfezia'' species are commonly known as desert truffles. Some authorities consider this the type genus of the family Terfeziaceae, although phylog ...
'' and ''
Tirmania The Terfeziaceae, or desert truffles, is a family of truffles ( ber, script=latn, Tirfas, ar, كمأ, Kam', ckb, دنبلان, Domalan, he, כמהת הנגב, kmehat hanegev) endemic to arid and semi-arid areas of the Mediterranean Region, N ...
'' of the family Terfeziaceae are known as the "desert truffles" of Africa and the Middle East. ''
Pisolithus tinctorius ''Pisolithus arhizus'' is a widespread Sclerodermataceae, earth-ball like fungus, which may in fact be several closely related species. Common names include dead man's foot and dyeball. It is known in Australia as the horse dung fungus, in Sout ...
'', which was historically eaten in parts of Germany, is sometimes called "Bohemian truffle". '' Geopora'' spp. are important ectomycorrhizal partners of trees in woodlands and forests throughout the world. ''Pinus edulis'', a widespread pine species of the Southwest US, is dependent on ''Geopora'' for nutrient and water acquisition in arid environments. Like other truffle fungi, ''Geopora'' produces subterranean sporocarps as a means of sexual reproduction. ''
Geopora cooperi ''Geopora cooperi'', commonly known as the pine truffle or the fuzzy truffle, is a species of fungus in the family Pyronemataceae. It has a fuzzy brown outer surface and an inner surface of whitish, convoluted folds of tissue. Widely distributed ...
'', also known as pine truffle or fuzzy truffle, is an edible species of this genus. ''
Rhizopogon ''Rhizopogon'' is a genus of ectomycorrhizal basidiomycetes in the family Rhizopogonaceae. Species form hypogeous sporocarps commonly referred to as "false truffles". The general morphological characters of ''Rhizopogon'' sporocarps are a simpl ...
'' spp. are ectomycorrhizal members of the Basidiomycota and the order Boletales, a group of fungi that typically form mushrooms. Like their ascomycete counterparts, these fungi can create truffle-like fruiting bodies. ''Rhizopogon'' spp. are ecologically important in coniferous forests where they associate with various pines, firs, and
Douglas fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Oregon pine, and Columbian pine. There are three va ...
. In addition to their ecological importance, these fungi hold economic value, as well. ''Rhizopogon'' spp. are commonly used to inoculate coniferous seedlings in nurseries and during reforestation. '' Hysterangium'' spp. are ectomycorrhizal members of the Basidiomycota and the order Hysterangiales that form sporocarps similar to true truffles. These fungi form mycelial mats of vegetative hyphae that may cover 25-40% of the forest floor in Douglas fir forests, thereby contributing to a significant portion of the biomass present in soils. Like other ectomycorrhizal fungi, ''Hysterangium'' spp. play a role in nutrient exchange in the nitrogen cycle by accessing nitrogen unavailable to host plants and acting as nitrogen sinks in forests. '' Glomus'' spp. are arbuscular mycorrhizae of the phylum Glomeromycota within the order Glomerales. Members of this genus have low host specificity, associating with a variety of plants including hardwoods, forbs, shrubs, and grasses. These fungi commonly occur throughout the Northern Hemisphere. Members of the genus ''
Elaphomyces ''Elaphomyces'' (‘deer truffles’) is a genus of hypogeous fungi in the family Elaphomycetaceae. The widespread genus contains 25 truffle-like species. ''Elaphomyces'' is one of the most important ectomycorrhizal fungal genera in temperate and ...
'' are commonly mistaken for truffles.


Ecology

The mycelia of truffles form
symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
, mycorrhizal relationships with the roots of several tree species, including
beech Beech (''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to temperate Europe, Asia, and North America. Recent classifications recognize 10 to 13 species in two distinct subgenera, ''Engleriana'' and ''Fagus''. The ''Engle ...
, birch,
hazel The hazel (''Corylus'') is a genus of deciduous trees and large shrubs native to the temperate Northern Hemisphere. The genus is usually placed in the birch family Betulaceae,Germplasmgobills Information Network''Corylus''Rushforth, K. (1999). ...
, hornbeam, oak, pine, and poplar. Mutualistic ectomycorrhizal fungi such as truffles provide valuable nutrients to plants in exchange for carbohydrates. Ectomycorrhizal fungi cannot survive in the soil without their plant hosts. In fact, many of these fungi have lost the enzymes necessary for obtaining carbon through other means. For example, truffle fungi have lost their ability to degrade the cell walls of plants, limiting their capacity to decompose plant litter. Plant hosts can also depend on their associated truffle fungi. ''Geopora'', ''Peziza'', and ''Tuber'' spp. are vital in the establishment of oak communities. ''Tuber'' species prefer argillaceous or calcareous soils that are well drained and neutral or
alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
. ''Tuber'' truffles fruit throughout the year, depending on the species, and can be found buried between the leaf litter and the soil. Most fungal biomass is found in the
humus In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...
and litter layers of soil. Most truffle fungi produce both asexual spores (mitospores or
conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...
) and sexual spores (meiospores or ascospores/ basidiospores). Conidia can be produced more readily and with less energy than ascospores and can disperse during disturbance events. Production of ascospores is energy intensive because the fungus must allocate resources to the production of large sporocarps. Ascospores are borne within sac-like structures called asci, which are contained within the sporocarp. Because truffle fungi produce their sexual fruiting bodies underground, spores cannot be spread by wind and water. Therefore, nearly all truffles depend on
mycophagous Fungivory or mycophagy is the process of organisms consuming fungi. Many different organisms have been recorded to gain their energy from consuming fungi, including birds, mammals, insects, plants, amoebas, gastropods, nematodes, bacteria and othe ...
animal vectors for spore dispersal. This is analogous to the dispersal of seeds in fruit of angiosperms. When the ascospores are fully developed, the truffle exudes volatile compounds that attract animal vectors. For successful dispersal, these spores must survive passage through the digestive tracts of animals. Ascospores have thick walls composed of
chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
to help them endure the environment of animal guts. Animal vectors include birds, deer, and rodents such as voles,
squirrel Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrels. Squ ...
s, and chipmunks. Many species of trees, such as '' Quercus garryana'', are dependent on the dispersal of sporocarps to inoculate isolated individuals. For example, the acorns of ''Q. garryana'' may be carried to new territory that lacks the necessary mycorrhizal fungi for establishment. Some mycophagous animals depend on truffles as their dominant food source. Flying squirrels, ''
Glaucomys sabrinus The northern flying squirrel (''Glaucomys sabrinus'') is one of three species of the genus '' Glaucomys'', the only flying squirrels found in North America.Walker EP, Paradiso JL. 1975. ''Mammals of the World''. Baltimore: Johns Hopkins Universit ...
'', of North America play a three-way symbiosis with truffles and their associated plants. ''G. sabrinus'' is particularly adapted to finding truffles using its refined sense of smell, visual clues, and long-term memory of prosperous populations of truffles. This intimacy between animals and truffles indirectly influences the success of mycorrhizal plant species. After ascospores are dispersed, they remain dormant until germination is initiated by exudates excreted from host plant roots. Following germination, hyphae form and seek out the roots of host plants. Arriving at roots, hyphae begin to form a mantle or sheath on the outer surface of root tips. Hyphae then enter the root cortex intercellularly to form the Hartig net for nutrient exchange. Hyphae can spread to other root tips colonising the entire root system of the host. Over time, the truffle fungus accumulates sufficient resources to form fruiting bodies. Rate of growth is correlated with increasing photosynthetic rates in the spring as trees leaf out.


Nutrient exchange

Truffle fungi receive carbohydrates from their host plants, providing them with valuable micro- and macronutrients. Plant macronutrients include potassium, phosphorus, nitrogen, and
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
. In contrast, micronutrients include iron, copper, zinc, and chloride. In truffle fungi, as in all ectomycorrhizae, the majority of nutrient exchange occurs in the Hartig net, the intercellular hyphal network between plant root cells. A unique feature of ectomycorrhizal fungi is the formation of the mantle on the outer surface of fine roots. Truffles have been suggested to co-locate with the orchid species ''
Epipactis helleborine ''Epipactis helleborine'', the broad-leaved helleborine, is a terrestrial species of orchid with a broad distribution. It is a long lived herb which varies morphologically with ability to self-pollinate. Description ''Epipactis helleborine'' can ...
'' and ''
Cephalanthera damasonium ''Cephalanthera damasonium'', the white helleborine, is a species of orchid. It is widespread across much of Europe, the Middle East and Asia. ''Cephalanthera damasonium'' is the type species of the genus '' Cephalanthera''. Description ''Cepha ...
'', though this is not always the case.


Nutrient cycling

Truffle fungi are ecologically important in nutrient cycling. Plants obtain nutrients via their fine roots. Mycorrhizal fungi are much smaller than fine roots, so they have a higher surface area and a greater ability to explore soils for nutrients. Acquisition of nutrients includes the uptake of phosphorus, nitrate or ammonium, iron, magnesium, and other ions. Many ectomycorrhizal fungi form fungal mats in the upper layers of soils surrounding host plants. These mats have significantly higher carbon and fixed nitrogen concentrations than surrounding soils. Because these mats are nitrogen sinks, leaching of nutrients is reduced. Mycelial mats can also help maintain the structure of soils by holding organic matter in place and preventing erosion. Often, these networks of mycelium provide support for smaller organisms in the soil, such as bacteria and microscopic arthropods. Bacteria feed on the exudates released by mycelium and colonise the soil surrounding them. Microscopic arthropods such as mites feed directly on mycelium and release valuable nutrients for the uptake of other organisms. Thus, truffle fungi and other ectomycorrhizal fungi facilitate a complex system of nutrient exchange between plants, animals, and microbes.


Importance in arid-land ecosystems

Plant community structure is often affected by the availability of compatible mycorrhizal fungi. In arid-land ecosystems, these fungi become essential for the survival of their host plants by enhancing the ability to withstand drought. A foundation species in arid-land ecosystems of the Southwest United States is '' Pinus edulis'', commonly known as pinyon pine. ''P. edulis'' associates with the subterranean fungi ''Geopora'' and ''Rhizopogon''. As global temperatures rise, so does the occurrence of severe droughts, detrimentally affecting the survival of aridland plants. This variability in climate has increased the mortality of ''P. edulis''. Therefore, the availability of compatible mycorrhizal inoculum can greatly affect the successful establishment of ''P. edulis'' seedlings. Associated ectomycorrhizal fungi will likely play a significant role in the survival of ''P. edulis'' with continuing global climate change.


Extraction

Because truffles are subterranean, they are often located with the help of an animal (sometimes called a truffler) possessing a refined sense of smell. Traditionally, pigs have been used to extract truffles. Both the female pig's natural truffle-seeking and her intent to eat the truffle were thought to be due to a compound within the truffle similar to androstenol, the sex pheromone of boar saliva, to which the sow is keenly attracted. Studies in 1990 demonstrated that the compound actively recognised by both truffle pigs and dogs is
dimethyl sulfide Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cook ...
. In Italy, the use of pigs to hunt truffles has been prohibited since 1985 because of damage caused by animals to truffle mycelia during the digging that dropped the production rate of the area for some years. An alternative to truffle pigs are dogs. Dogs offer an advantage because they do not have a strong desire to eat truffles, so they can be trained to locate sporocarps without digging them up. Pigs attempt to dig up truffles. Fly species of the genus '' Suilla'' can also detect the volatile compounds associated with subterranean fruiting bodies. These flies lay their eggs above truffles to provide food for their young. At ground level, ''Suilla'' flies can be seen flying above truffles.


Volatile constituents

The mycelia or fruiting bodies release the volatile constituents responsible for the natural aroma of truffles or derive from truffle-associated
microbe A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s. The chemical ecology of truffle volatiles is complex, interacting with plants, insects, and mammals, which contribute to
spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
dispersal. Depending on the truffle species, lifecycle, or location, they include: *
Sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
volatiles Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances. On planet Earth, the term ' ...
, which occur in all truffle species, such as dimethyl mono- (DMS), di- (DMDS) and tri- (DMTS) sulfides, as well as 2-methyl-4,5-dihydrothiophene, characteristic of the white truffle ''T. borchii'' and
2,4-Dithiapentane 2,4-Dithiapentane is an organosulfur compound. It is a colorless liquid with a strong odor. 2,4-Dithiapentane is the dimethyldithioacetal of formaldehyde. It is prepared by the acid-catalyzed condensation of methyl mercaptan, the main aromatic c ...
occurring in all species but mostly characteristic of the white truffle ''T. magnatum''. Some very aromatic white truffles are notably pungent, even irritating the eye when cut or sliced. * Metabolites of nonsulfur amino acid constituents (simple and branched-chain hydrocarbons) such as
ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene i ...
(produced by mycelia of white truffles affecting root architecture of host tree), as well as 2-methylbutanal, 2-methylpropanal, and
2-phenylethanol Phenethyl alcohol, or 2-phenylethanol, is the organic compound that consists of a phenethyl group (C6H5CH2CH2) attached to OH. It is a colourless liquid that is slightly soluble in water (2 ml/100 ml H2O), but miscible with most organic solvents. ...
(also common in baker's yeast). * Fatty acid-derived volatiles (C8-alcohols and aldehydes with a characteristic fungal odor, such as 1-octen-3-ol and 2-octenal). The former is derived from linoleic acid and produced by mature white truffle ''T. borchii''. * Thiophene derivatives appear to be produced by bacterial symbionts living in the truffle body. The most abundant of these, 3-methyl, 4-5 dihydrothiophene, contributes to the white truffle's aroma. Several truffle species and varieties are differentiated based on their relative contents or absence of
sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds lar ...
s, ethers or
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
s, respectively. The sweaty-musky aroma of truffles is similar to that of the pheromone androstenol that also occurs in humans. , the volatile profiles of seven black and six white truffle species have been studied.


Culinary use

Because of their high price and their strong aroma, truffles are used sparingly. Supplies can be found commercially as unadulterated fresh produce or preserved, typically in a light
brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for br ...
. Their chemical compounds infuse well with fats such as butter, cream, cheeses, avocados, and coconut cream. As the volatile aromas dissipate quicker when heated, truffles are generally served raw and shaved over warm, simple foods where their flavour will be highlighted, such as buttered pasta or
egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the a ...
s. Thin truffle slices may be inserted into
meat Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
s, under the skins of roasted fowl, in '' foie gras'' preparations, in '' pâtés'', or in stuffings. Some speciality
cheese Cheese is a dairy product produced in wide ranges of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. During production, ...
s contain truffles, as well. Truffles are also used for producing truffle salt and truffle honey. While chefs once peeled truffles, in modern times, most restaurants brush the truffle carefully and shave it or dice it with the skin on to make the most of the valuable ingredient. Some restaurants stamp out circular discs of truffle flesh and use the skins for sauces.


Oil

Truffle oil Truffle oil is a modern culinary ingredient used to impart the flavor and aroma of truffles to a dish. The ingredient is commonly used as a finishing oil in a variety of dishes, including truffle fries, pasta dishes, pizzas, and puréed foods such ...
is used as a lower-cost and convenient substitute for truffles, to provide flavouring, or to enhance the flavour and aroma of truffles in cooking. Some products called "truffle oils" contain no truffles or include pieces of inexpensive, unprised truffle varietals, which have no culinary value, simply for show. The vast majority is oil that has been artificially flavoured using a synthetic agent such as
2,4-dithiapentane 2,4-Dithiapentane is an organosulfur compound. It is a colorless liquid with a strong odor. 2,4-Dithiapentane is the dimethyldithioacetal of formaldehyde. It is prepared by the acid-catalyzed condensation of methyl mercaptan, the main aromatic c ...
. The scientific name is included on the ingredient list of truffle oils infused with natural truffles.


Vodka

Because more aromatic molecules in truffles are soluble in alcohol, they can carry a more complex and accurate truffle flavour than oil without synthetic flavourings. Many commercial producers use 2,4-dithiapentane regardless, as it has become the dominant flavour most consumers, unexposed to fresh truffles but familiar with oils, associate with them. Because most Western nations do not have ingredient labelling requirements for spirits, consumers often do not know if artificial flavourings have been used. It is used as a spirit in its own right, a
cocktail A cocktail is an alcoholic mixed drink. Most commonly, cocktails are either a combination of spirits, or one or more spirits mixed with other ingredients such as tonic water, fruit juice, flavored syrup, or cream. Cocktails vary widely across ...
mix or a food flavouring.


See also

* Chocolate truffle – a confection named for its similar appearance to a truffle * List of ''Tuber'' species * Specialty foods


References


Additional resources

* * * *


External links


Website of the North American Truffling Society

Website of the Australian Truffle Growers
{{DEFAULTSORT:Truffle (Fungus) Edible fungi French cuisine Fungi in cultivation Italian cuisine Mushroom types Fungus common names