Mushrooms of the order of truffles belong to the group of hypogean
(underground) Ascomycetes. This order includes about 100 species a
specific character of which is underground fruit bodies - they are
usually called truffles.
Truffles are mushrooms that are not widely known these days, actually
they are almost forgotten. Information about their locations in our
country is very scarce. But there were times when they were widely
famous and were in high demand as a valuable product. Most often
truffles grow in warm regions of temperate zone, especially in
France, Italy, Spain, Portugal, southern regions of Germany , in the
southwest and in the moderate climate zone of European part of Russia.
Outside Europe they are known in North Africa and California.
Fruit bodies of truffles are round or tuber-like, of fleshy or
gelatinous consistency, for most species closed when mature. The size
of truffle fruit bodies (depending on the species) can range from a
hazel nut to a large potato tuber or even larger, and their weight
sometimes reaches 1 kg. The outer part of a truffle fruit body is
differentiated as a leathery layer - peridium, which on the outside
can be smooth, cracked or covered with large or small polyhedral
warts. When cut, fleshy tissue of the mushroom has a distinctive
marble pattern consisting of alternating light and dark veins. First
veins are called inner veins and the second - outer veins. In some
species of truffles (Tuber excavatum, T. rufum) all outer veins meet
in one point on the surface of the fruit body where its shell breaks
and they open outside. Others - for example, summer truffle (T.
aestivum) have several such points on the surface. Outer veins
alternate with inner ones which are denser. They come out of outer
parts under the common shell and all curve to the same point.
Asci of truffles are located inside the fruit body or on inner veins,
forming something similar to hymenial layer (while outer veins look
like very wrinkled sheets), or in nest-looking way in ascocarps. This
property is considered a systematic character. Asci of truffle
mushrooms can be of various shape. They can be round, oval,
club-shaped, sack-like, less often - cylindrical, containing 1, 2, 4
or 8 spores. Ascospores are always unicellular, colorless or
gray-brown, of round or elliptic shape. Their shell is usually
reticulate or echinulate, warty. Releasing of spores happens passively
after complete destruction of ascocarp or when they are eaten by
animals.
At early stages of development fruit bodies are located among a dense
entanglement of mycelium in a close connection with it; they look like
little round bodies. At the end of winter or in early spring one can
discern separate inner tissues in them and even clearly see the color
and structure of the surface. Later mycelium disappears, and the ripe
fruit body lies in the soil by itself or just touches the mycelium
with its more or less prominent base (Ghoiromyces and Terfezia
genera). At young stages of development of the mushroom Tuber
excavatum embryos of fruit bodies appear as open saucer-looking
formations, on the concave and somewhat wrinkled surface of which
embryos of hymenial layer arise as a palisade-structured layer of
paraphysis. During later development the embryonic ascocarp located in
the soil doesn't have the opportunity to grow width-wise. Therefore it
forms numerous wrinkles on the surface of hymenium and later shrinks
its initially widely opened aperture into a narrow hole, that is the
point where outer veins open. The hymenium covering them first
consists of paraphysis which eventually grows, intertangles with
similar paraphysis growing from the opposite wrinkle and fills gaps
between them with a spongy plexus of hyphae, thus forming outer veins.
On the boundary between inner and outer veins among the paraphysis
asci develop; they don't form a normal hymenial layer. They often
contain less than eight spores as a result of early degeneration of
some of them. Mushrooms of Choiromyces genus, while having similar
initial development, have hymenium growing not on all the surface of
wrinkles but only in the deepest parts; their upper areas join
together so that the opening of outer veins disappears. Because of
this feature in the mature fruit body the hymenium with asci inlays
closed groove-looking cavities which are not connected with each
other. Despite all the differences between mature fruit bodies of
truffle mushrooms and apoteciums of discomycetes, their ontogenetic
development shows significant similarities, which gives a reason to
conclude truffles from discomycetes and, more precisely, from
Pezizales order.
So, fruit bodies of truffles can be defined as underground very
wrinkled apoteciums. Based on this foundation some taxonomists
consider truffles to be an order of a group of discomycetes. Truffle
mushrooms are a good example of the influence of life conditions on
the morphology of fruit body. Ascocarps of truffles rejoin, with the
help of peridium defending asci developing inside from the pressure of
soil. Typical hymenium of discomycetes loses its initial features, and
asci lose their cylindrical shape and orderly location, which can be
explained by no need to actively disseminate spores, and they are only
released with general destruction of the fruit body. In the family of
truffles asci form hymenial layer. Fruit bodies don't turn into
powder at maturity.
This family is represented by genera: Balsamia, Choiromyces,
Stephensia, Tuber.
In the family of Terfezia asci are located nest-like inside fruit
bodies; they don't turn into powder at maturity. The family includes
the following genera: Picoa, Tirmania, Terfezia. Some authors also
include the family of Elaphomycetaceae in this order. Truffles prefer
spongy calciferous, somewhat ferrous soil resulting from weathering of
pure or loamy limestone, which is not very suitable for other plants.
For such soil it is typical that in the presence of lime rotting plant
remnants (fallen leaves and sticks) easily decay while producing a lot
of nitrogen products, which are used by the mushroom's mycelium.
Truffle mushrooms necessarily need to form a mycorrhiza, and
therefore they grow in the neighborhood of seed plants. For example,
black truffles (Tuber melanosporum, T. aestivum) grow in forests with
oak, beech, hornbeam, hazelnut. These trees and a special type of soil
are a favorable condition for truffle growing. White truffles (Ò.
magnatum, Choiromyces meandriformis) grow in broadleaf forests
together with birch, poplar, elm, basswood, willow, ash or hawthorn.
Sometimes truffles form mycorrhiza with such trees as juniper, fir or
pine. Mushrooms from Terfezia genus form mycorrhiza with plants of
rockrose family. Truffle mycelium usually produces from 3 to 7 fruit
bodies arranged as a circle, nest-like. When mature they raise the
soil, which serves as a sign for mushroom hunters. Every year such
nests grow and expand, and if the mycelium is not broken, in such
places (called truffle places) a harvest of mushrooms can be expected
in the following years. For their full development truffles require
from 3 to 4 months, and several kinds of them ripen from summer to
winter. For example, winter truffle (Ò. brumale) ripens from November
till February, summer truffle (Ò. aestivum) - in June and July.
Underground fruit bodies are not harmed by frosts up to -6 °Ñ, though
when they are on the surface, they easily get affected by cold and
lose their taste with even minor frosts.
Truffles are highly valued by gourmets of many countries. Some of them
are known since ancient times. Among truffles of practical value, real
black French truffle (Ò. melanosporum) is undoubtedly considered the
most precious and important; it is also called Perigord truffle (this
is the name of the province where it grows).
Fruit bodies of black French truffle are angular-round, with large
warts and point-looking deepenings on the surface, reddish- or
grayish-brownish-black color, of size from a walnut to a medium-sized
apple. Flesh reddish, violet black or grayish-brownish-red when
mature, with black and white veins which have red brims. Asci contain
4-6 black-brownish ascospores, ornamented with sharp spines.
This truffle ripens in autumn and is harvested until winter. Its fruit
bodies are in the highest demand and have persistent strong aroma.
Real black truffle is in large quantities harvested in southern
France; it can also be found in Switzerland, northern Italy and very
rarely - in southern regions of Germany. Winter and summer truffles
are more widespread territorially; because of it they are used for
food more often. Another group of truffles used for food - white
truffles. Wonderful aroma and delicate flavor of a real black-spored
truffle determine a continuous high demand for these mushrooms.
However, because of symbiotic nature of truffles' life champignon-like
artificial growing of them doesn't succeed.
Only in southern France and in Italy so-called "indirect" way of
industrial truffle-growing is used, for which they build artificial
truffle plantations. They take acorns, preferably from an oak forest
where truffles grow, sow them in an appropriate soil; make special
nests and place there the soil taken from truffle places and
containing spores and mycelium. After 10-12 years first truffles
appear under little oaks. Fruit bodies can be harvested every year, if
the sowings are constantly thinned out. Truffle nests are marked by
dry grass and somewhat elevated soil, reminding of molehills.
Mass truffle harvesting in France uses trained dogs and pigs. Because
of their nature pigs easily find these mushrooms to eat them. The
animals are attracted by the smell of truffles, and they are able to
sniff them from up to 20 m. For training one should take 3-4 months
old females; they can be used until they are 12-15 years old. When the
pig finds truffles and starts to dig, one should hit it at the nose
with a short stick, force the pig away - and dig out the fruit bodies.
The pig should be given boiled beans, peas or corn as a reward.
However, the pig usually gets tired soon, and the work with it stops.
If the mushrooms grow on light sand soil and the nests are scattered
far from each other, it is reasonable to use dogs, which in addition
don't get tired as often as pigs and can run around a larger
territory.
Using dogs for truffle hunting has been known in Italy since XV
century. Any dog breeds can be used, but short-legged ones - poodles,
pooches - turn out to be the best. Hunter dogs are unsuitable for
truffle hunting. Until 60s of XIX century trained bears were used for
truffle harvesting around Moscow. For training dogs one should choose
females and accustom them to truffles since puppy age. First they are
given milk with added truffle broth, later - bread with addition of
truffles. When the puppies grow up a little, they are first trained in
a room with hidden pieces of wood rubbed with truffles. The puppy is
given food upon finding them. Then they are trained in the yard, in
the garden, and finally, in the forest. A dog easily gets used to such
hunt. It sniffs the ground and barks when it finds truffles.
Residents of French provinces Perigord and Veacluse practice
so-called "fly hunting" based on the fact that flies of certain
species (truffle flies - Helomyza gigantea ) lay eggs in the ground
near truffles. Their larvae feed on tissues of these mushrooms. So,
flying of these insects points at the presence of truffles.
|
