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****Work is from the existing truffle article. Sections that were modified were copied and pasted into my sandbox.
A truffle is the fruiting body of a subterranean ascomycete 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, Leucangium, and over a hundred others.[1] These genera belong to the class Pezizomycetes and the Pezizales order. There are several truffle-like basidiomycetes excluded from Pezizales including Rhizopogon and Glomus. Truffles are ectomycorrhizal fungi and are therefore usually found in close association with tree roots. Spore dispersal is accomplished through fungivores, animals that eat fungi.[2] These fungi have significant ecological roles in nutrient cycling and drought tolerance.
Some of the truffle species are highly prized as food. French gourmet Jean Anthelme Brillat-Savarin called truffles "the diamond of the kitchen".[3] Edible truffles are held in high esteem in French[4], Italian, Ottoman, Middle Eastern and Spanish cuisine, as well as in international haute cuisine. Truffles are cultivated agriculturally and are also harvested from natural habitats.
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.[5] Within the order Pezizales, subterranean fungi evolved independently at least fifteen times.[5] Contained within Pezizales are the families Tuberaceae, Pezizaceae, Pyronematacae, and Morchellaceae. All of these families contain lineages of subterranean or truffle fungi.[1] 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 fossilize.[6] Molecular clockwork has suggested the evolution of ectomycorrhizal fungi occurred approximately 130 million years ago.[7]
The evolution of subterranean fruiting bodies has arisen numerous times within the Ascomycota, Basidiomycota, and Glomeromycota.[1] For example, the genera Rhizopogon 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.[8] Phylogenetic evidence suggests that the majority of 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 utilizing animals.[8]
The phylogeny and biogeography of the genus Tuber was investigated in 2008[9] using internal transcribed spacers (ITS) of nuclear DNA and revealed five major clades (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. 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.[10]
The truffle habit has evolved independently among several basidiomycete genera.[11][12][13] Phylogenetic analysis has revealed that basidiomycete subterranean fruiting bodies, like their ascomycete counterparts, evolved from above ground mushrooms. For example, it is likely that Rhizopogon species arose from an ancestor shared with Suillus, a mushroom forming genus.[11] Studies have suggested that selection for subterranean fruiting bodies among ascomycetes and basidiomycetes occurred in water-limited environments.[8][11]
Black truffle
The black truffle or black Périgord truffle (Tuber melanosporum), the second-most commercially valuable species, is named after the Périgord region in France.[14] Black truffles associate with oaks, hazelnut, cherry, and other deciduous trees and are harvested in late autumn and winter.[14][15] The genome sequence of the black truffle was published in March 2010.[16]
Summer or burgundy truffle
The black summer truffle (Tuber aestivum) is found across Europe and is prized for its culinary value.[17] Burgundy truffles (designated Tuber uncinatum, but the same species) are harvested in autumn until December and have aromatic flesh of a darker colour. These associate with various trees and shrubs.[17]
White truffle
Tuber magnatum, the high-value white truffle or trifola d'Alba Madonna ("Truffle of the White Madonna" in Italian) is found mainly in the Langhe and Montferrat areas of Italy[18] of the Piedmont region in northern Italy and, most famously, in the countryside around the cities of Alba and Asti.[19]
Whitish truffle
The "whitish truffle" (Tuber borchii) is a similar species found in Tuscany, Abruzzo, Romagna, Umbria, the Marche and Molise. It is not as aromatic as those from Piedmont, although those from Città di Castello come quite close.[15]
Geopora species
Geopora spp. are important ectomycorrhizal partners of trees in woodlands and forests throughout the world.[20] Pinus edulis, a widespread pine species of the Southwest, is dependent on Geopora for nutrient and water acquisition in arid environments.[21] Like other truffle fungi, Geopora produces subterranean sporocarps as a means of sexual reproduction.[21] Geopora cooperi, also known as pine truffle or fuzzy truffle, is an edible species of this genus.[20]
Other species
A less common truffle is "garlic truffle" (Tuber macrosporum).
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, Oregon spring white truffle; and Tuber oregonense, the Oregon winter white truffle. Kalapooya brunea, the Oregon brown truffle, has also been commercially harvested and is of culinary note.
The pecan truffle (Tuber lyonii)[22] syn. texense[23] 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".[24] 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.[25]
Truffle-like species
The term "truffle" has been applied to several other genera of similar underground fungi. The genera Terfezia and Tirmania of the family Terfeziaceae are known as the "desert truffles" of Africa and the Middle East. The basidiomycete "Hart's truffle" is a name for Elaphomycetaceae. Pisolithus tinctorius, which was historically eaten in parts of Germany, is sometimes called "Bohemian truffle".[26]
Rhizopogon spp. are ectomycorrhizal members of the Basidiomycota and the order Boletales, a group of fungi that typically form mushrooms.[27] Like their ascomycete counterparts, these fungi are capable of creating truffle-like fruiting bodies.[27] Rhizopogon spp. are ecologically important in coniferous forests where they associate with various pines, firs, and Douglas-fir.[28] 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.[27]
Hysterangium spp. are ectomycorrhizal members of the Basidiomycota and the order Hysterangiales that form sporocarps similar to true truffles.[29] 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.[29] Like other ectomycorrhizal fungi, Hysterangium play a role in nutrient exchange in the nitrogen cycle by accessing nitrogen unavailable to host plants and by acting as nitrogen sinks in forests.[28]
Glomus spp. are arbuscular mycorrhizae of the phylum Glomeromycota within the order Glomerales.[8] Glomus spp. that form truffle-like fruiting bodies are some of the most ancient subterranean fungi. Glomus species vary in the diversity of their spore-bearing structures. While some produce truffle-like fruiting bodies, many have naked spores or rudimentary sporocarps.[30] Members of this genus have low host specificity, associating with a variety of plants including hardwoods, forbs, shrubs and grasses.[8] These fungi commonly occur throughout the Northern hemisphere.[8]
The mycelia of truffles form symbiotic, mycorrhizal relationships with the roots of several tree species including beech, birch, hazel, hornbeam, oak, pine, and poplar.[31] Mutualistic ectomycorrhizal fungi such as truffles provide valuable nutrients to plants in exchange for carbohydrates.[32] Ectomycorrhizal fungi lack the ability to survive in the soil without their plant host.[5] 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.[5] Plant hosts can also be dependent on their associated truffle fungi. Studies have demonstrated that Geopora, Peziza, and Tuber spp. are vital in the establishment of oak communities.[33]
Tuber species prefer argillaceous or calcareous soils that are well drained and neutral or alkaline.[34][35][36] Tuber truffles fruit throughout the year, depending on the species, and can be found buried between the leaf litter and the soil. The majority of fungal biomass is found in the humus and litter layers of soil.[28]
Most truffle fungi produce both asexual spores (mitospores or conidia) and sexual spores (meiospores or ascospores/basidiospores).[37] 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.[37] 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 via wind and water. Therefore nearly all truffles depend on mycophagous animal vectors for spore dispersal.[1] This is analogous to the dispersal of seeds in fruit of angiosperms. When the ascospores are fully developed, the truffle will begin to exude volatile compounds that serve to attract animal vectors.[1] For successful dispersal, these spores must survive passage through the digestive tracts of animals. Ascospores have thick walls composed of chitin to help them endure the environment of animal guts.[37] Animal vectors include birds, deer, and rodents such as voles, squirrels, and chipmunks.[1][33][38] 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.[33] Some mycophagous animals depend on truffles as their dominant food source. Flying squirrels, Glaucomys sabrinus, of North America play a role in a three-way symbiosis with truffles and their associated plants.[39] Glaucomys sabrinus is particularly adapted to finding truffles using its refined sense of smell, visual clues, and long-term memory of prosperous populations of truffles.[39] 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.[40] Following germination, hyphae will form and seek out the roots of host plants. Arriving at roots, hyphae will begin to form a mantle or sheath on the outer surface of root tips. Hyphae will then enter the root cortex intercellularly to form the Hartig net for nutrient exchange. Hyphae can spread to other root tips colonizing the entire root system of the host.[40] Over time, the truffle fungus accumulates sufficient resources to form fruiting bodies.[40][33] Rate of growth is correlated with increasing photosynthetic rates in the spring as trees leaf out.[33]
Nutrient exchange
In exchange for carbohydrates, truffle fungi provide their host plants with valuable micro and macronutrients. Plant macronutrients include potassium, phosphorus, nitrogen, and sulfur whereas micronutrients include iron, copper, zinc, and chloride.[32] 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 outer surface of fine roots.[32]
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 and therefore have a higher surface area and a greater ability to explore soils for nutrients. Acquisition of nutrients includes the uptake of phosphorus, nitrogen, iron, magnesium and other ions.[32] Many ectomycorrhizal fungi form fungal mats in the upper layers of soils surrounding host plants. These mats have significantly higher concentrations of carbon and fixed nitrogen than surrounding soils.[41] Because these mats are nitrogen sinks, leaching of nutrients is reduced.[28] Mycelial mats can also help maintain the structure of soils by holding organic matter in place and preventing erosion.[8] 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 colonize soil surrounding them.[42] Microscopic arthropods such as mites feed directly on mycelium and release valuable nutrients for the uptake of other organisms.[43] Thus, truffle fungi, along with 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.[44][45] In arid-land ecosystems, these fungi become essential for the survival of their host plants by enhancing ability to withstand drought.[46] A foundation species in arid-land ecosystems of the Southwest United States is Pinus edulis, commonly known as pinyon pine. Pinus edulis associates with the subterranean fungi Geopora and Rhizopogon.[47] As global temperatures rise, so does the occurrence of severe droughts detrimentally affecting the survival of arid-land plants. This variability in climate has increased the mortality of P. edulis.[48] Therefore, the availability of compatible mycorrhizal inoculum can greatly affect the successful establishment of P. edulis seedlings.[47] Associated ectomycorrhizal fungi will likely play a significant role in the survival of P. edulis with continuing global climate change.
 |
| Truffle dog | Truffle hog |
|---|---|
| Keen sense of smell | Keen sense of smell |
| Must be trained | Innate ability to sniff out truffles |
| Easier to control | Tendency to eat truffles once found |
Because truffles are subterranean, they are often located with the help of an animal possessing a refined sense of smell. Traditionally, pigs have been utilized for the extraction of truffles.[49] Both the female pig's natural truffle-seeking, as well as her usual intent to eat the truffle, are 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 recognized by both truffle pigs and dogs is dimethyl sulfide.[49]
In Italy, the use of the pig 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 pose an advantage in that they do not have a strong desire to eat truffles and can therefore be trained to locate sporocarps without digging them up. Pigs will attempt to dig up truffles.[49]
Fly species of the genus Suilla can also detect the volatile compounds associated with subterranean fruiting bodies. These flies will lay their eggs above truffles to provide food for their young. At ground level Suilla can be seen flying above truffles.[49]
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