cologically, mushrooms can be classified into three groups: the saprophytes, the parasites and the mycorrhizae. Although this book centers on the cultivation of gourmet and medicinal
saprophytic species, other mushrooming! also discussed.
Mycorrhizal mushrooms form a mutually dependent, beneficial relationship with the roots of host plants, ranging from trees to grasses "Myco" means mushrooms while "rhizal" means roots. The filaments of cells which grow into the mushroom body are called the mycelium. The mycelia of mycorrhizal mushrooms can form an exterior sheath covering the roots of plants and are called ectomycorrhizal Or they can invade the :nterior root cells of host plants and these are called endomycorrhizal. In either case, both organism? benefit from this association. Plant growth is accelerated.
The resident mushroom mycelium increases the plant's absorption of nutrients, nitrogenous compounds, and essential elements (phosphorus, copper and zinc). By growing beyond the immediate root zone, the mycelium channels and concentrates nutrients from afar. Plants with mycorrhizal fungal partners can also resist diseases far better than those without.
Most ecologists now recognize that a forest's health is directly related to the pres ence, abundance and variety of mycorrhizal associations. The mycelial component of top soil within a typical Douglas fir forest in the Pacific Northwest approaches 10% of the total biomass. Even this estimate may be low, not taking into account the mass of the endomycorrhizae and the many yeast-like fungi that thrive in the topsoil.
The nuances of climate, soil chemistry and predominant microflora play determinate roles in the cultivation of mycorrhizal mushrooms in natural settings. I am much more inclined to spend time attempting the cultivation of native mycorrhizal species than to import exotic candidates from afar. Here is a relevant example-
Truffle orchards are well established in France, Spain and Italy, with the renowned Perigold black truffle, Tuber melanosporum, fetching up to $500 per lb. (See Figure 7). Only in the past 30 years has tissue culture of Truffle mycelium become w'dely practiced, allowing the development of planted Truffle orchards. Land owners seeking an economic return without resorting to cutting trees are naturally attracted to this prospective investment. The idea is enticing. Think of having an orchard of oaks or filberts, yielding pounds of Truffles per year for decades at several hundred dollars a pound! Several companies in this country have, in the past 12 years, marketed Truffle-inoculated trees for commercial use. Calcareous soils (i. fl high in calcium) in Texas, Washington and Oregon have been suggested as ideal sites. Tens of thousands of dollars have been exhausted in this endeavor. Ten years after planting, I know of only one, possibly two. successes with this method. This discouraging state of affairs should be fair warning to investors seeking profitable enterprises in the arena of Truffle cultivation. Suffice it to say that the only ones to have made money in the Truffle tree industry are those who have resold "inoculated" seedlings to other would-be trufflateurs
A group of Oregon trufflateurs has been attempting to grow the Oregon White Truffle, Tuber gibbossum. Douglas fir seedlings have been inoculated with mycelium from this na
Figure 7. A Truffle market in France.
tive sper 'es and planted in plots similar to Christmas tree farms. Several years passed before the harvests began. However, since Oregon White Truffles were naturally occurring nearby, whether or not the inoculation process actually caused the truffles to form is unclear
Mycorrhizal mushrooms in Europe have suffered a rad-cal decline in years of late while the saprophytic mushrooms have increased in numbers. The combined effects of acid rain and other industrial pollutants, even the disaster at Chernobyl, have been sug gested to explain the sudden decline of both the quantity and diversity of wild mycorrhizal mushrooms. Most mycologists believe the sudden availability of dead wood is re sponsible for the comparative :ncrease :n the numbers of saprophytic mushrooms. The decline in Europe portends, in a worst case scenario, a total ecological collapse of the mycorrhizal community. In the past ten years the diversity of the mycorr1 :zal mushrooms in Europe has fallen by more than 50%! Some species, such as the Chanterelle, have all but disappeared from regions in the Netherlands, where it was abundant only 20 years ago. (See Arnolds, 1992; Leek, 1991). Many biologists vr-ew these mushrooms as indicator species, the first domino to fall in a series leaa-ng to the failure of the forest's life-sup port systems.
One method for inoculating mycorrliizae calls for the planting of young seedlings near the root zones of proven mushroom-producing trees. The new seedlings acc 'mate and become "infected" wi h the mycorrhizae of a neighboring, parent tree. In ihis fashion, a second generation of trees carrying the mycorrhizal fungus is generated. After a few
Figure 9. Scanning electron micrograph of mycelium encasing the root of a tree after mycorrhization.
years the new trees are dug up and replanted into new environments. This method has had the longest tradition of success in Europe.
Another approach, modestly successful, is to dip the exposed roots of seedlings into water enriched with the spore mass of a mycorrhizal candidate. First, mushrooms are gathered from the wild and soaked in water. Thousands of spores are washed off of the gills resulting in an enriched broth of inoculum. A spore-mass slurry coming from several mature mushrooms and diluted into a 5-gal Ion bucket can inoculate a hundred or more seedlings. The concept is wonderfully simple. Unfortunately, success is not guaranteed.
Broadcasting spore mass onto the root zones of likely candidates is another avenue that costs little in time and effort. Habitats should be selected on the basis of their paral lels in nature. For instance, Chanterelles can be found in oak forests of the midwest and in Douglas fir forests of the west. Casting spore mass of Chanterelles into forests similar to those where Chanterelles proliferate :s obviously the best choice. Although the success rate is not high, the rewards are well worth the minimum effort involved. Bear in mind that tree roots confirmed to be mycorrhized with a gourmet mushroom will not necessarily result in harvestable mushrooms. Fungi and their host trees may have long associations without the appearance of edible fruitbodies (For more information, consult Fox (1983)).
On sterilized media, most mycorrhizal mushrooms grow slowly, compared to the saprophytic mushrooms. Their long evolved dependence on root by-products and complex soils makes media preparation inherently more complicated. Some mycorrhizal species, like Pisolithus tinctorius, a puffball favoring pines, grow quite readily on sterilized media. A major industry has evolved providing foresters with seedlings inoculated with this fungus. Mycorrhized seedlings are healthier and grow faster than non mycorrhized ones Unfortunately, the gourmet mycorrhizal mushroom species do not fall into the readily cultured species category. The famous Matsutake (Tricholonia magnivelare) may take weeks before its mycelium fully colonizes the medium on a single petri dish! Unfortunately, this rate of growth is the rule rather than the exception with the majority of gourmet mycorrhizal species.
Chanterelles are one of the most popularly collected wild mushrooms. In the Pacific Northwest of North America the harvesting of Chanterelles has become a controversial, multi-million dollar business. Like Matsutake, Chanterelles (Cantharellus cibarius) also form mycorrhizal associations with trees. Additionally, they demonstrate a unique interdependence on soil yeasts. This type of mycorrhizal relationship makes tissue culture most difficult. At least three organisms must be cultured simultaneously: the host tree, the mushroom, and soil yeasts. A red soil yeast, Rhodotorula glutinis, is crucial in stimulating spore germination. The Chanterelle life cycle may have more dimensions of biological complexity. Currently, no one has grown Chanterelles to the fruitbody stage under laboratory conditions. Not only do other microorganisms play essential roles, the timing of their introduction appears critical to success in the mycorrhizal theater.
Senescence occurs with both saprophytic and mycorrhizal mushroom species. Often the first sign of senescence is not the inability of mycelium to grow vegetatively, but the loss of the formation of the sexually repro-
during organ: the mushroom. Furthermore, the slowness from sowing the mycelium to the final stages of harvest confounds the quick feed-back all cultivators need to refine their techniques. Thus, experiments trying to mimic how Chanterelles or Matsutake grow may take 20-40 years each, the age the trees must be to support healthy, fruiting colonies of these prized fungi. Faster methods are clearly desirable, but presently only the natu ral model has shown any clue to success.
Given the huge hurdle of time for honing laboratory techniques, I favor the "low-tech" approach of planting trees adjacent to known producers of Chanterelles, Matsutake, Truffles and Boletes. After several years the trees can be uprooted, inspected for mycor-rhizae and replanted :n new en-'iionments. The value of the contributing forest can then be viewed, not in terms of board feet of lumber, but in terms of its ability for creating satellite, mushroom/tree colonies. When industrial or suburban development threatens entire forests, and is unav 'dable, future-oriented foresters may corr'der the removal of the mycorrhizae as a last-ditch effort to salvage as many mycologicai communities as possible by s:mple transplantation techniques, although on a much grander scale.
Until laboratory techniques evolve to estab lish a proven track record of successful marriages that result in harvestable crops, I hesitate to recommend mycorrhizal mushroom cultivation as an economic endeavor. Mycor rli zal cultivation pales n comparison to the predictability of growing saprophytic mushrooms ike Oyster and Shiitake. The industry simply needs the benefit of many more years of mycologicai research to better decipher the compiex models of mycorrhizal mushrooms
Parasi; c Mushrooms: Blights of the Forest?
Parasitic fun^l have been the bane of foresters. They do immeasurable damage to the health of rendent tree species, bui in the process, create new habitats for many other organisms. Although the ecological damage caused by parasitic fungi is well understood, we are only just learning of their importance in the forest ecosystem. Comparatively few mushrooms are true parasses
Parasites iive off a host plant, endangering the host's health as it grows. Of all the parasitic mushrooms that are edible, the Honey Mushrooms, Armiîlaria mellea, are the best known. One of these Honey Mushrooms, known as Am Hlaria bulbosa, made national headlines when scientists reported finding a single colony covering 37 acres, weighing at least 220 000 lbs. with an estimated age of 1500 years! With the exception of the trembling Aspen forests of Colorado, this fungus is the largest-known, living organism on the planet. And, it ;s a marauding parasite!
In the past, a parasitic fungus has been looked upon as being biologically evil. This
view is rapidly changing as science progresses. A new parasitic fungus attacking the Yew tree has been recently discovered by Montana State University researchers. This new species is called Taxomyces andreanae for one notable feature: it produces minute quantities of the potent anti-carcinogen taxol, a proven shrinker of breast cancer. (S'one. 1993). If this new fungus can be grown in suffi cient quantities in liquid culture, the potential value of the genome of parasHc fungi takes on an entirely new dimension.
Many saprophytic fungi can be weakly parasitic in their behavior, especially if a host tree is dying from other causes. These can be called facultative parasites: saprophytic fungi activated by favorable conditions to behave parasitically. Some parasitic fungi continue to grow long after their host has died. Oyster mushrooms (Pleurotus ostreatus) are classic saprophytes, although they are frequently found on dying cottonwood, oak, poplar, birch, maple and alder trees These appear to be operating parasitically when they are only exploiting a rapidly evolving ecological n; he.
Many parasitic fungi are microfungi and are barely visible to the naked eye. In mass, they cause the formation of cankers and shoot blights. Often their preeminence in a imddle-aged forest is symptomatic of other imbalances within the ecosystem Acid rain, ground water pollution, insect damage, and loss of protective habitat all are contributing factors unleashing parasitic fungi After a tree dies, from parasitic fungi or other causes, saprophytic fungi come into play.
Most of the gourmet mushrooms ate saprophytic, wood-decomposing fungi Ihese saprophytic fungi are the premier recycles on the planet. The filamentous mycelial network is designed to weave between and through the cell walls of plants. The enzymes and acids they secrete degrade large molecular complexes into simpler compounds. All ecosystems depend upon fungi's ability to decompose organic plant matter soon after it is rendered available. The end result of their activity is the return of carbon, hydrogen, nitrogen and minerals back nto the ecosystem in forms usable to plants, usects and other organisms As decomposers, they can be separated into three key groups. Some mushroom species cross over from one cat-egoiy tc another depenc';ng upon prevailing conditions.
Primary Decomposers: These are the
fungi first to capture a twig, a blade of grass, a chip of wood a log or stump. Primary decomposers are typically fasi-growing, sending out ropey strands of mycelium that quickly attach to and decompose plant tissue Most of the decomposers degrade wood, Hence, the majority of these saprophytes are woodland species, such as Oyster mushrooms (Pleurotus species), Shiitake (Lentinula edodes) and King Stropharia (Strophara rugoso-annulata). However, each species has developed specific sets of enzymes to break down lignin-cellulose, the structural components of most plant cells Once I he enzymes of one mushroom species have broken down the lignin-cellulose to its fullest potential, other saprophytes utilizing their own repertoire of enzymes can reduce this material even further.
Secondary Decomposers: These mushrooms rely on the previous activity of other fungi to partially break down a substrate to a state wherein they can thrive Secondary decomposers typically grow from composted material. The actions of other fungi, actino-mycetes, bacteria and yeasts all operate within a compost. As plant residue is degraded by these microorganisms, the mass, structure and composition of the compost is reduced. Heac, carbon dioxide, ammonia and other gases are emitted as by-products of the composting process. Once these microorganisms (especially actinomycetes) have completed tin :r life cycles, the compost is susceptible to invasion by a select secondary decomposer A classic example of a secondary decomposer is the White Button Mushroom, Agaricus brunnescens, the most commonly cultivated mushroom* Another example is Stropharia ambigua which invades outdoor mushroom beds after wood chips have been first decomposed by a primary saprophyte.
Tertiary Decomposers: An amorphous group, the fungi represented by this group are typically soil dwellers. They survive in habitats that are years in the making from the activity of the primary and secondary decomposers. Fungi existing in these reduced substrates are remarkable in that the habitat appears inhospitable for most other mushrooms. A classic example of a tertiary decomposer is Aleuria aurantia, the Orange Peel Mushroom. This complex group of fungi often pose unique problems to would-be cultivators. Panaeolus subbalteatus is yet another example. Although one can grow it on composted substrates, this mushroom has the reputation of growing prolifically in :he discarded compost from Button mushroom farms. Other tertiary decomposers include species of Conocybe, Agrocybe, Pluteus and some Agaricus species.
The floor of a forest is constantly being replenished by new organic matter. Primary, secondary and tertiary decomposers can all occupy the same location. In the complex environment of the forest floor, a "habitat" can actually be described as the overlaying of several habitats mixed into one. And, over time, as each habitat is being transformed, successions of mushrooms occur. This model becomes infinitely complex when taking into account the
* The cultivation of this mushroom is covered in detail in The Mushroom Cultivator (1983) by Stamets & Chilton, inter-relationships of not only the fungi to one another, but the fungi to other micro-organisms (yeast?, bacteria, protozoa), plants, insects and mammals.
Primary and secondary decomposers afford the most opportunities for cultivation. To select the best species for cultivation, several variables must be carefully matched.
Climate, available raw materials, and the mushroom strains all must interplay for cultivation to result in success. Native species are the best choices when you are designing outdoor mushroom landscapes.
Temperature-tolerant varieties of mushrooms are more forgiving and easier to grow than those which thrive within finite temperature limits. In warmer climates, moisture is typically more rapidly lost, narrowing the opportunity for mushroom growth. Obviously, growing mushrooms outdoors in a desert climate is more difficult than growing mushrooms in moist environments where they naturally abound. Clearly, the site selec tion of the mushroom habitat is crucial. The more exposed a habitat is to direct mid-day sun, the more difficult it is for mushrooms to flourish.
Many mushrooms actually benefit from indirect sunlight, especially in the northern latitudes. Pacific Northwest mushroom hunters have long noted that mushrooms grow most prolifically, not in the darkest depths of a woodlands, but in environments where shade and dappled sunlight are combined. Sensitivity studies to light have established that various species differ in their optimal response to wave-bands of sunlight. Nevertheless, few mushrooms enjoy prolonged exposure to direct sunlight.
The Global Environmental Shift and The Loss of Species Diversity
Studies in Europe show a frightening loss of species diversity in forestlands, most evident with the mycorrhizal species. Many mycologists fear many mushroom varieties, and even species, will soon become extinct. As the mycorrhizal species decline in both numbers and vanety, the populations of saprophytic and parasitic fungi initially rise, a direct result of the increased availability of dead wood debris. However, as woodlots are burned and replanted, the complex mosaic of the natural forest is replaced by a highly uniform, mono-species landscape. Because the replanted trees are nearly identical in age, the cycle of debris replenishing the forest floor is interrupted. This new "ecosystem" cannot support the myriad of fungi insects, small mammals, birds, mosses and flora so characteristic of ancestral forests. In pursuit of commercial forests, the native ecology has been supplanted by a biologically anemic woodlot. This woodlot landscape is barren in terms of species diversity.
With the loss of every ecological niche, the sphere of bio-diversity shrinks. At some pres ently unknown level, the diversity will fall below the critical mass needed for sustaining a healthy forestland. Once passed, the forest may not ever recover without direct and drastic counter-action: the insertion of multi-age trees, of different species, with varying canopies and undergrowth. Even with such extraordinary action, the complexly of a replanted forest can not match that which has evolved for thousands of years. Little is understood about prerequisite microflora—yeasts, bacteria, micro-fungi—upon which the ancient forests are dependent. As the number of species declines, whole communities of organisms disappear. New associations are likewise limited. If this trend continues, I believe the future of new forests, indeed the planet, is threatened.
Apart from the impact of wood harvest, the health of biologically diverse forests is in increasing jeopardy due to acid rain and other airborne toxins. Eventually, the populations of all fungi—saprophytic and mycorrhizal— suffer as the critical mass of dead trees declines more rapidly than it is replenished. North Americans have already experienced the results of habitat-loss from the European forests. Importation of wild picked mushrooms from Mexico, United States and Canada to Europe has escalated radically in the past twenty years. This increase in demand is not just due to the growing popularity of eating wild mushrooms. It is a direct reflection of the decreased availability of wild mushrooms from regions of the world suffering from ecological shock The woodlands of North America are only a few decades behind the forests of Europe and Asia.
With the loss of habitat of the mycorrhizal gourmet mushrooms, market demands for gourmet mushrooms should shift to those that can be cultivated. Thus, the pressure on this not-yet renewable resource would be alleviated, and the judicious use of saprophytic fungi by homeowners as well as foresters may well prevent wivlespread parasitic disease vectors. Selecting and controlling the types of saprophytic fungi occupying these ecological niches can benefit both forester and forestland.
THE ROLE OF MUSHROOMS IN NATURE
Many saprophytic fungi benefit from catastrophic events in the forests. When hurricane-force winds rage across woodlands, enormous masses of dead debris are generated. The older trees are especially likely to fall. Once the higher canopy is gone, the growth of the younger, lower canopy of trees is triggered by the suddenly available sunlight The continued survival of young trees is dependent upon the quick recycling of nutrients by the saprophytic fungi.
Every time catastrophes occur—hurricanes, tornadoes, volcanoes, floods, even earthquakes—the resulting dead wood becomes a stream of inexpensive substrate materials. In a sense, the cost of mushroom production is underwritten by natural disasters. Unfortunately, to date, few individuals and communh^s take advantage of catastrophia as fortuitous events for mushroom culture. However, once the economic value of recycling with gourmet and medicinal mushrooms is clearly understood and with the increasing popularity of backyard cultivation, catastrophia can be viewed as a positive event, at least in terms of providing new economic opporturj"cs for those who are mycologically astute.
In heavily industrialized areas, soils are often contaminated with a wide variety of pollutants, particularly petroleum-based com pounds, polychlorinated biphenols (PCB's). heavy metals, pesticide-related compounds, and even radioactive wastes. Mushrooms grown in polluted environments can absorb toxins directly .ito their tissues. As a result,
mushrooms grown in these environments should not be eaten. Recently, a visitor to Ternobyl, a city about 60 miles from Chernobyl, the site of the world's worst nuclear power plant acc dent, returned to the United States with ajar of pickled mushrooms. The mushrooms were radioactive enough to set off Geiger counter alarms as the baggage was being processed. The mushrooms were promptly confiscated by Customs officials. Unfortunately, most toxins are not so readily detected.
A number of fungi can, however, be used to detoxify contaminated environments, a process called "bioremediatii n". The white rot fungi (particularly Phanerochaete chrysosporium) and brown rot fungi (notably Gloephyllum species) are the most widely used. Most of these wood-rotters produce lig nin peroxidases and cellulases which have unusually powerful degradative properties. These extracellular enzymes have evolved to break down plant fiber, primarily lignin-cel-lulose, the structural component in woody plants, into simpler forms. By happenstance, these same enzymes also reduce recalcitrant hydrocarbons and other man-made toxins. Given the number of industrial pollutants that are hydrocarbon-based, fungi are excellent candidates for toxic waste clean-up and are viewed by scientists and government agen cies with increasing interest. Current and prospective future uses include the detoxification of PCB (polychlorolbiphenols), PCP (pentachlorophenol), oil, pesticide/herbicide residues, and even are being explored for ameliorating the impact of radioactive wastes.
Bioremediation of toxic waste sites is especially attractive because the environment is treated in situ. The contaminated soils do not have to be hauled away, eliminating the extraordinary expense of handling, transportation, and storage. Since these fungi have the ability to reduce complex hydrocarbons into elemental compounds, these compounds pose no threat to the environment. Indeed, these former pollutants could even be considered as "fertilizer", helping rather than harming the nutritional base of soils.
Dozens of bioremediation companies have formed to solve the problem of toxic waste. Most of these companies look to the imperfect fungi The higher fungi should not be disqualified for bioremediation just because they produce fruitbody. Indeed, this group may hold answers to many of the toxic waste problems. The most vigorous rotters described in this book are the Ganodenna and
Pleurotus mushrooms. However, mushrooms grown from toxic wastes are best not eaten as residual toxins may be concentrated within the mushrooms.
The mycelium is fabric of interconnected, interwoven strands of cells. A colony can be the size of a half-dollar or many acres. A cubic inch of soil can host up to a mile of mycelium. This organism can be physically separated, and yet behave as one.
The exquisite lattice-like structure of the mushroom mycelium, often referred to as the mycelial network, is perfectly designed as a filtration membrane. Each colony extends long, complex chains of cells that fork repeatedly in matrix-like fashion, spreading to geographically defined borders. The mushroom mycelium, being a voracious forager for carbon and nitrogen, secretes extracellular enzymes that^glock organic complexes. The newly frem)™: -ents are then selectively absorbed clDwlplhrough the cell walls into the mycelial network.
In the rainy season, water carries nutritional particles through this filtration membrane, including bacteria, which often become a food source for the mushroom mycelium. The resulting downstream effluent is cleansed of not only carbon/nitrogen-rich compounds but also bacteria, in some cases nematodes, and legions of other micro-organisms. Only recently has the classic saprophyte, the voracious Oyster mushroom, been found to be parasitic against nematodes. (See Thorn & Barron, 1984). The extracellular enzymes act like an anesthetic and stun the nematodes, thus allowing the invasion of gA .'■ f,i ¡«JSEU1IJ
the mycelium directly into their immobilized bodies.
The use of mycelium as a mycofilter is currently being studied by this author in the removal of biological contaminants from surface water passing directly into sensitive watersheds. By placing sawdust implanted with mushroom mycelium in drainage ba sins downstream from farms raising livestock, the mycelium acts as a s;-;ve which traps fecal bacteria and ameliorates the impact of a farm's nitrogen-rich outflow into aquatic ecosystems. This concept is incorpo rated into an integrated farm model and explored in greater detail in Chapter 5: Permaculture with a Mycological Twist.
any mushroom hunters would love to have their favorite edible mushroom growing in their backyard. Who would not want a patch of Matsutake, Shaggy Manes, giant Puffballs or the stately Prince gracing their property? As the different seasons roll j along, gourmet mus hrooms would arise in concert. Practically speak- I ing. however, our knowledge of mushroom cultivation is currently i limited to 100 species of the 10,000 thought to exist throughout the j world. Through this book and the works of others, the number of j cultivatible species will enlarge, especially if amateurs are encour- | aged to boldly experiment. Techniques for cultivating one species j may be applied for cultivating another, often by substituting an ingredient, changing a formula, or altering the fruiting environment, j Ironically, with species never before grown, the strategy or' "benign neglect" more often leads to success than active interference with the natural progression of events. I have been particularly adept at this non-strategy. Many of my early mushroom projects only produced when I left them alone.
A list of candidates which can be grown using current methods follows. At present we do not know how to grow those species marked by an asterisk (*). However, I believe techniques for their cultivation will soon be perfected, given a little experimentation. This list is by no means exclusive, and will be much amended in the future. Many of these mushrooms are described as good edibles in the field guides, as listed in the resource section of this book. (See Appendix IV.).
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