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Cultivation of Mushrooms
Introduction
The large, macroscopic, spore-bearing, fruiting bodies of fungi are generally referred to as mushrooms. Under the proper environmental conditions, their mycelia become tightly interwoven to give rise to the structure we call the mushroom. However, the conditions under which mushrooms form are poorly known. As a result, relatively few species of mushrooms can be cultivated. Species of mushrooms may be designated as edible/medicinal or poisonous and the former will be the topic of this web page.
Today, there are more species of mushrooms cultivated throughout the world than were available in the past. Prior to the 1970s, in Western cultures, only one species, The Button Mushroom, Agaricus bisporus (J.E. Lange) Imbach, was commonly cultivated. This species is grown on a substrate composed of composted horse manure and straw. Most edible mushrooms, available in Western cultures, during this same period, were not cultivated. These species were either collected in wooded areas by individuals for personal consumption or sold to markets for commercial consumption. Because most of the latter species form mycorrhizae, they were usually only available once a year, for a short period of time, during the normal fruiting period for the species.
In Eastern cultures, prior to the 1970s, different species were being cultivated. These species were typically those that grew on woody substrate and were cultivated on logs. These included the Shiitakes, Lentinula edodes (Berk.)Pegler, the Wood Ear, Auricularia polytricha (Mont.) Sacc. and the Enoke, Flammulina velutipes (Curtis) Singer, to name a few.
Because the knowledge that fungi reproduced by spores would not be known until the 19th Century, the method initially used in the early cultivation of mushrooms was far different than those carried out today. Early cultivation of mushrooms, involved collecting the fruit bodies of these mushrooms from their natural habitat and taking them to a vicinity of "fresh" substrate, where their spores would germinate and colonize the substrate, eventually giving rise to fruitbodies. As was the realization that diseases could be passed on from individuals to individuals, it seems likely that the same line of reasoning was applied to growing mushrooms. However, growing mushrooms is not like growing wheat or any other agricultural crop. Even with all the research that has been carried out in mushroom cultivation, the exact conditions under which mushrooms fruit, is still not known for most species. The exact conditions for fruiting even those mushrooms that can be cultivated and are even profitable are still obscure.
We will discuss some of the better known species from both Western and Eastern cultures. In these species, several methods of cultivation is used, composted waste material of various origin, cut logs, sterilized sawdust in polypropylene bags (heat resistant plastic bags), and inoculation of mushroom mycelium to the roots of living trees for mycorrhizal species.
In addition to their food value, some species also appear to have medicinal value as well.
Agaricus bisporus, Button Mushroom
Agaricus bisporus (Fig. 1) is a species with which just about everybody is familiar and is commonly referred to as the Button Mushroom. It is also the most cultivated mushroom in the world, but in Western culture, it was also the only species available until around the late 1970s.
The following summary of the history of A. bisporus cultivation in caves and houses is summarized from Delmas (1978), Edwards (1978) and Dwyer (2010). The cultivation of this species began around 1650, in Paris France, in areas in which mushrooms were frequently collected on used compost from melon crops. For approximately 160 years, A. bisporus was grown in open fields. At some point, it was realized that mycelium, or what is referred to as the spawn of the mushroom, was what gave rise to the mushroom and could be utilized much like the seed of plants to grown mushrooms. Another significant discovery was light was not necessary for fruiting A. bisporus, which led to its successful cultivation in natural caves, quarries or excavated tunnels. The advantage of cultivating A. bisporus in caves was the cool, moist, uniform environment. In 1910, France began growing A. bisporus in mushroom houses, but caves are still the preferred growing structures for the production of mushrooms in France. Cultivation of A. bisporus eventually spread to England, and by 1865, had reached the United States. At first, spawn for the mushroom was imported from England, but because of the time involved in shipping, the mushroom spawn was in poor condition by the time it had reached the United States and produced a poor quality of mushrooms. It would not be until 1903 before United States Department of Agriculture scientists developed its own spawn, thereby freeing the United States of its dependence upon English spawn, which had caused so many problems. Louis F. Lambert, a French mycologist, started the American Spawn Company of St. Paul Minnesota, the first producer of pure mushroom spawn in the United States. His product was sold across the country as "Lambert’s Pure Culture Spawn." This spawn received a silver medal at the Universal Exposition in St. Louis in 1904. A measure of Lambert’s success was that English spawn was soon being sold under the name "English Pure Culture Spawn." By 1914, four to five million pounds of mushrooms were grown in the United States. The production cost to the mushroom grower ranged from fifteen to twenty-five cents a pound and retailed at forty to sixty cents per pound, and marketing aimed at the consumers became very important. Mushrooms were packed in attractive containers to make a good looking product that sold better. Growers of mushrooms, at first, were "back yard" operations and was not their main source of income. From there it became a large industry in certain parts of the country, with Southeastern Pennsylvania being the largest center for mushroom production in the country, a position that it has maintained to this day. In 1924, 85% of the mushrooms grown in this country were from Pennsylvania. In 1930, the U.S. Census Bureau revealed that there were 516 growers in the U.S. and that 350 were in Chester County, Pennsylvania.
Pennsylvania State University also became a major factor in the growth of the U.S. mushroom industry helping improve productivity dramatically in the 70’s and 80’s allowing growers to produce more and more mushrooms per unit area.
Growing Agaricus bisporus
Although the conditions that are optimal for growing A. bisporus is known, the actual process is still poorly understood because the substrate on which it grows is one which is undefined. The substrate on which A. bisporus is cultivated include horse manure, wheat straw, corn cobs, several other plant wastes and some animal wastes such as feather meal and chicken manure (Fig. 2). The composting process is a mixed fermentation involving a range of microorganisms, bacteria and other fungi, which will degrade some of the complex compounds such as lignin and cellulose. Due to the biological activities of the microorganisms, the compost will become very hot, and provide an environment that will be restricted to only a few microorganisms that will be heat tolerant. When the compost cools, it will have a consistency similar to that of thick oatmeal and will provide an environment well suited for mycelial growth of A. bisporus. Another way in which you can look at the compost, at this stage, is that it is now A. bisporus’ turn to decompose and colonize the substrate. Mycelial growth, at this point, is very rapid if maintained at the optimal temperature of 24 C. However, this temperature will vary according to the variety, which is being grown. Following growth of mycelium throughout the substrate, a casing layer, is placed over the substrate. The casing layer is normally composed rich, clay soil, which is nutritionally poor, relative to the compost on which the mycelium has been growing. The casing layer is critical in the fruiting body formation of A. bisporus and is necessary for the initiation of fruiting. Why this is important is not known, but without this step fruiting will not occur. The biological activity of bacteria, various soluble salts, together with the lowering of the temperature between 14-18 C, will optimize fruiting body production of A. bisporus. Formation of fruitbodies begin as mycelial strands, just below the surface of the casing layer, develop "nodules" which are composed of tightly interwoven mycelium that will eventually develop into button mushrooms (Fig. 3-4). Fruitbodies of the Button Mushroom are harvested before their caps expand.
Figure 1: Cultivated Agaricus bisporus.
from http://en.wikipedia.org/wiki/File:101-0114_IMG.JPG
Figure 2: Manure compost ready to be inoculated, from Tom Volk, http://botit.botany.wisc.edu/toms_fungi/apr2001.html. Figure 3: Agaricus bisporus fruiting, from cased substrate. http://www.tactic-tech.com/img/im/white-button-mushroom-agaricus-bisporus/agfig6.jpg
Figure 4: Sectioned layers, from bottom to top, compost, spawn, casing layer and mushrooms. From Anton Sonnenborg, Wageningen University, Netherlands.
"Varieties" of Agaricus bisporus
While there is only one mushroom that is sold as the white Button Mushroom, there are two, variants of A. bisporus, Crimini (Fig. 5) and Portobello (Fig. 6). The Crimini is a brown variety of the Button Mushroom. Both the Crimini and Button Mushrooms are harvested before the cap of the mushrooms have expanded. Thus, their gills are not visible. The Portobello is a mature version of the Crimini where the mushrooms has been harvested after the cap has expanded and the dark brown gills are visible. The Portobello is a more mature and much larger mushroom than either of the "button mushrooms".
Left image, Figure 5: "Crimini" variety of A. bisporus from http://www.terawarner.com/hhh/images/mushroom.jpg Right Image, Figure 6: "Portobello" variety from http://upload.wikimedia.org/wikipedia/commons/3/3e/Portobello_mushrooms.jpg
Auricularia auricula and Auricularia polytricha, Ear Fungus
These two species are two of the most popular edible species, among the jelly fungi. Auricularia auricula (L.) Underw. is a temperate species while A. polytricha (Fig. 7) is tropical in their distribution. The earliest record of A. polytricha cultivation was documented in about 200-300 BC (Reviewed in Cheng and Tu, 1978). The species is now known and has now been cultivated throughout the South Pacific and Asia. Regardless of where it is utilized, it has a common name which makes reference to the ear-shaped fruiting body, Mu-Erh (wood ear) in China, and Pepeiao (ear) in Hawai‘i, just to name a few. The fruiting bodies are usually brownish to reddish brown and has a consistency of jelly. In nature, the two species are saprotrophic that grow on logs. Thus, the cultivation of these species differs from that of A. bisporus in that they will require a wood based substrate. The process for cultivating the two Auricularia species is the same as that of other wood decomposers, such as the Shiitake and the Oyster Mushrooms.
Currently, the most commonly utilized method of commercial cultivation of wood decomposing fungi is a sawdust-grain medium that has been sterilized. Auricularia polytricha will be used to illustrate this type of cultivation. The proportion of sawdust to grain is variable, but in growing A. polytricha, Wong and Wells (1987) used a six part sugar cane bagasse to one part old fashion rolled oats medium (Fig. 8). The bagasse and rolled oats were mixed with an equal volume of tap water. Excess water was squeezed out and 900 ml of the mixture was placed loosely into a 1 L beaker. The beaker was then covered with a 23.5 cm2 sheet of aluminum foil, placed on top of a paper towel of equal area. A rubber band was used to secure the cover on the beaker, which was then autoclaved for 90 minutes at 121 C. After the medium cooled it was inoculate with the fungus and allowed to incubate in the dark, at 25 C, for approximately 4 weeks, the time that was required for the mycelium to permeate the substrate (Fig. 9-10). The substrate was then removed from the beaker and placed in a greenhouse, with diffused light and a relative humidity of approximately 85% that was maintained by an automatic misting system. Fruitbody formation occurred in about 3-4 weeks (Fig. 11). This method has also been successful in fruiting A. fuscosuccinea (Fig. 12) and A. delicata [Fig. 13] (Wong, 1993).
Figure 7: Auricularia polytricha fruiting on log.
Figure 8: Sugar cane and old fashion rolled oats medium.
Figure 9: Medium after autoclaving and inoculated. Mycelial growth has permeated substrate.
Figure 10: Substrate after removal from beaker. On right early fruiting has occurred.
Figure 11: Mature fruiting bodies of A. polytricha.
Figure 12: Mature fruiting bodies of A. fuscosuccinea.
Figure 13: Mature fruiting bodies of A. delicata.
Commercially, species of Auricularia are cultivated in polypropylene bags with filters (Fig. 14) that will allow air flow, but will exclude spores and microorganisms from entering into the substrate.
Figure 14: Saw dust medium in polypropylene bags used in commercial cultivation of wood decomposing mushrooms. From http://jovenz.files.wordpress.com/2009/01/incubation1.jpg.
Oyster Mushrooms
Members of the genus Pleurotus are commonly called Oyster Mushrooms. All members are saprotrophic and a number of different species have been cultivated. The most commonly cultivated species is Pleurotus ostreatus (Fig. 15) and can frequently be collected in Europe and North America. This species has become common in supermarkets since the 1970s and since that time a number of other species in the genus has become available as well. Oyster mushrooms can be recognized by their short, eccentric stalks, i.e. not centrally attached and fragile fruit body.
Previous to their cultivation, Oyster Mushrooms were popular edible species among mushroom collectors who delight in going out and collecting their own mushrooms for consumption. Its cultivation was first described at the beginning of the 20th Century (Reviewed by Zadražil, 1978), on cut logs. By placing logs, with fruiting bodies, near the prepared cut logs that had been prepared for cultivation of P. ostreatus. The spores from the fruiting bodies would eventually infect the nearby, uninoculated logs and fruiting would eventually occur. However, this method was inefficient since the cut logs may become infected with another species of mushroom or not be infected, at all. This method was first used in China approximately 800 years ago in the cultivation of Shiitake mushrooms (Reviewed by Ito, 1978).
To ensure that each log would be inoculated with the correct mushroom, a means was developed to inoculate the spawn into the logs. Wooden dowels (Fig. 16), such as those used in carpentry, were placed in a container in which the P. ostreatus mycelium was growing to allow the mycelium to grow through the dowels. Holes were then drilled into the cut logs, to be inoculated, and the infected wooden dowels hammered into the holes (Fig. 17-18). The hole inoculated with the infected dowel was then covered with parafilm (Fig. 19) to prevent drying. The logs are then kept moist and, within 6-9 months, the fruitbodies will begin to emerge (Fig. 20). The logs will continue to produce for as long as several years. However, due to intense cultivation of wood decomposing mushrooms, suitable logs began to be more difficult to find.
Figure 15: Pleurotus ostreatus.
Figure 16: Wooden dowels
Figures 17-19: Inoculation of inoculated wooden dowels into log. Figure 17: Drilling holes in logs. Figure 18: Inoculated dowel hammered into log and Figure 19: Seal dowel with parafilm. Images from http://www.turkeycountrymagazine.com/11JF/MembersOnly/feature_growing_shiitake_mushrooms.html
Block, et al. (1958), developed an important innovation, in which sawdust was used as the substrate material for growing wood inhabiting mushrooms and would become important, not only in cultivation of Pleurotus, but all cultivated mushrooms that grow on wood. This process is not only more ecologically sound, since it utilizes waste material as the substrate on which cultivation of the mushroom is to occur, but also it shortens the period of fruitbody formation to approximately two months. Currently, the use of a sterilized sawdust medium in polypropylene bag, as described for Auricularia, above, is the most popular method of cultivation for the different species of Pleurotus. In addition to P. ostreatus, other species cultivated include P. djamor (Rumph. ex Fr.) Boedijn. var. roseus Corner [Fig. 21], P. columbinus Quél., [Fig. 22] P. citrinopileatus Singer and P. eryngii (DC.) Quél., [Fig. 23] to name a few.
from from http://www.permacultureinbrittany.com/2010/02/woodland-mushroom-cultivation.html
.Figure 20: Mature Pleurotus
Figure 21: Left image, Pleurotus djamor var. roseus (Pink Oyster Mushroom), Figure 22 P. columbinus (Blue Oyster Mushroom) from http://www.mushroomsinbend.org/wp-content/uploads/2010/04/Oyster-bags.26-2.jpg Figure 22: Middle image, Pleurotus citrinopileatus (Golden Oyster Mushroom) [Figure 23] from http://upload.wikimedia.org/wikipedia/commons/9/92/Limonenseitlinge_%28Pleurotus_citrinopileatus%29_-_20100828.jpg and Figure 23: Right image, P. eryngii (Trumpet Oyster Mushroom).
Mushrooms Cultivated in Eastern Countries
Lentinus edodes, the Shitake or Forest Mushroom
Lentinula edodes (Fig. 24), the Shiitake Mushroom is as common in Asian countries as A. bisporus is in the West. Unlike the latter species, L. edodes was most often sold dried, in the United States, but because cultivation of this species is now common place, fresh Shiitake is now available at the supermarket. The species is medium size, with a cap diameter of approximately 2-4" and a stalk that is 4-5" long and approximately 0.75-1" thick. The cap is brown and "scaly," i.e. with upright warts, while the stipe is yellowish-white with a prominent, persistent annulus. The Shiitake has the distinctive advantage of a much longer shelf-like because they are more commonly sold dried while most other mushrooms are sold fresh.
The methods of cultivation of Shiitake duplicates that of P. ostreatus, but had occurred much earlier. The laying of fruiting bodies near freshly cut oak logs in order to cultivate Shiitake was reliably recorded, from China, approximately 800 years ago. As in P. ostreatus, it would not be until the late 19th Century that wooden dowels, with mycelium, would be used to inoculate cut logs. Presently, sterilized sawdust in polypropylene bags are used in the cultivation of Shiitake, as was described for P. ostreatus.
According to Chang and Miles (2004) the origin of Shiitake cultivation is credited to Master Wu San Kwung, in Qingyuan, China, during the Sung Dynasty (960-1127 A.D.) . He was regarded as the God of Mushroom by the local shiitake farmers. During these 800 years, shiitake cultivation has been the traditional industry for the people of Qingyuan and has spread to 200 counties in 11 provinces over China. From then on, shiitake had began the new era of bringing up wealth and health to the people. Qingyuan is historically regarded as "the Town of Shiitake" and "the Town Of Shiitake Farmers" and Qingyuan County has held a " China Shiitake Festival", annually.
A great deal of research has been carried out, in Japan, on the nutritional and medicinal value of the Shiitake. It is said to be rich in vitamin D2, and has anti-tumor activity polysaccharides.
Volvariella volvacea, Paddy Straw Mushroom
Volvariella volvacea (Bull.) Singer [Fig. 25] is probably one that all of you have consumed if you have ever dined in a Chinese restaurant. Many recipes call for this particular species of mushrooms. The mushroom is large. The cap, if allowed to mature, often exceeding 5" in diameter, and is light to dark gray. When young, the mushroom is entirely enclosed in a white, egg-like structure called the volva. As the mushroom develops, the stalk will elongate and push the cap upward, thereby rupturing the volva, leaving only a cup-like structure at the base of the stalk (see picture on left). However, it is often picked for eating while barely opening from its volva.
When this species was first cultivated is unknown, but it is thought to be Chinese, in origin, and is believed by Chang (1977) to have possibly started as recently as 1822. It is still cultivated mostly in the subtropical to tropical parts of China or Southeast Asian countries, where Chinese have migrated. It seems likely that the introduction of this species to Hawai‘i occurred during the plantation era, when the Chinese migrated to Hawai‘i to find work. As the common name implies, the Paddy Straw mushroom was usually grown on paddy straw, but other plant material are also presently used. Here in Hawaii, it occurs naturally in compost piles of sugar cane bagasse or wood mulch.
Although the yield is not high, paddy straw was practically the only material used to prepare the substrate for cultivation of the Paddy Straw Mushroom under natural conditions, even though other substrates had been successfully used. These other substrates included rice straw, dried banana leaves and oil palm bunch waste. However, the yield utilizing the latter substrate is substantially lower than even that of paddy straw. Thus, for a long time, this species was not very profitable as a commercial mushroom. It was not until 1970, when cotton waste was introduced as a substrate that there was a substantial gain in yield, and by 1973, cotton waste had completely replaced paddy straw, in cultivation of this species in Hong Kong (Chang, 1974). This eventually led to the Paddy Straw Mushroom becoming semi-industrialized in Hong Kong, Thailand, Taiwan and Indonesia. The cultivation method of this species is more comparable to that of Agaricus bisporus in that both grown on compost. The Paddy Straw Mushroom differs, however, in the material that is used for composting. In the case of cotton waste, the following proportion of substrates is used: Cotton waste with 4% rice or wheat straw and 4-6% ground agricultural limestone are mixed and allowed to ferment for 2-3 days. The composting pile is turned at least once and then pasteurized with steam.
The Paddy Straw Mushroom is presently grown in a number of Asian countries and the methods vary because of availability of technology to the growers. In Malaysia, paddy straw continues to be used as a substrate since 2 million tons of rice straw is produced annually. In Singapore, paddy straw is again used, but cotton waste, banana leaves are also used.
Tremella fuciformis, Silver Ear
Tremella fuciformis (Fig. 25) produces a white, lobed, irregularly shaped fruiting body. It is a species that has been long utilized as a "herb" to cure many ailments. It is listed as a folk remedy in old pharmacological, Chinese books, and is said to be a remedy for tuberculosis, high blood pressure, the common cold and to extend life expectancy. However, it is also considered a delicacy and, prior to its cultivation, was affordable only for the tables of the rich. For many years, it was believed that this species was a wood decomposer as is the Shiitake and Ear Fungus. However, it is now known to be a parasite on species of Ascomycota that are usually found growing nearby on the same log as T. fuciformis. A fungus that is parasitic on another fungus is said to be a mycoparasite. Thus, in order to grow this species, the host fungus must first be inoculated into the substrate and allowed to grow for a period of time and the T. fuciformis is later inoculated and will derive its nutrition on the host fungus and not from the woody material. This species occurs in Hawai‘i, but not commonly.
Flammulina velutipes, Enoki
The Enoki (Fig. 26) is a very small, delicate mushroom. The species is whitish-yellow, with a cap not more than ¼- ½ " in diameter. The stalk is approximately 3-4" long and about ¼" thick. It is cultivated on sawdust medium in large, urn-shaped containers. It would seem to be an unlikely candidate for cultivation because of its small size, but is commonly sold in the United States, in supermarkets.
The origin of cultivation of this species is believed to be in Japan, but its history is even more obscure than other species, which we have discussed. However, it has been cultivated for at least several centuries.
Some "Cultivated" Ascomycota
Tuber melanosporum (Black Truffle) and Related Species
Figure 24: Shiitake grown from a sawdust medium. Image courtesy of Lucy Inouye.
Figure 25: Volvariella volvacea.
Figure 25: Tremella fuciformis
Figure 26: Flammulina velutipes
Figure 27: Tuber melanosporum, Black Truffle
Figure 28: Tuber magnatum, The White Truffle: Sectioned fruiting body on left.
The truffles are a category onto themselves. They are undoubtedly the most sought after delicacy among the fungi, with a market price of approximately $1000 per pound for the Black Truffle,Tuber melanosporum Vittid. (Fig. 27), in 2011 and the White Truffle, T. magnatum Picco (Fig. 28), in 2001, sold for between $1000 to $2200. There are a number of species in the genus Tuber, but only a handful of those that occur in Europe are considered to be delicacies. Unlike the previous species discussed. Truffles are members of the Ascomycota and produce asci and ascospores during sexual reproduction. Also, they cannot be cultivated by the methods discussed above because they form mycorrhizae with oaks, hazelnuts and beeches.
The following summary of the history of truffles is reviewed from Delmas (1978). The gathering of truffles has been recorded as far back as 1600 BC and many early scientist speculated on their origin and nature in the universe. Theophrastus was the credited as the first to hypothesize that truffles were "plants" and came about as the result of rain from thunder storms. Unlike most mushrooms, truffles are subterranean, i.e. they grow underground. This undoubtedly led to confusion as to their origin and place in the universe. It would not be until 1885 that Frank, a German plant pathologist, discovered the true nature of truffles and their role in the mycorrhizal relationship with the roots of trees. His theory, however, was not universally embraced even in the early part of the 20th. Century. In 1903, de Gramont still believed that truffles were a product of the trees with which they were associated. The relationship of mycorrhizal fungi with their tree host is a complex one, and even with the tremendous resources that have been allocated in studying this relationship, mycologists still do not understand the environmental conditions that induce fruiting bodies to form. Various methods of cultivating truffles have been tried, but all have failed. Thus, for centuries the truffle industry relied upon collections from nature, but early this century, particularly during the world wars, demand for truffles fell and prices dropped. Tees, which supported the truffle fungus were cut down and land was developed for more profitable crops. After World War II demand grew again, however supply was inadequate and prices became exorbitant. It was the increase in demand that prompted researchers to find a means for increasing the supply of truffles to meet demand. It would not be until 1972 that Grente and Delmas proposed the most logical means of propagating truffles, which was to inoculate the fungus to the host tree.
In 1977, a great deal of land was put aside in order to start plantations of various species of European oaks and hazel trees, which were inoculated with the truffle mycelium. The time required before the first harvest could be harvested was approximately ten years. This method of truffle cultivation was successful and has produced a reliable source for the world's truffle supply. As long as the trees remain healthy, truffles will continue to be produced without further inoculation of the fungus. However, other countries desired truffle crops of their own. Capitalizing on this method, some business people began selling saplings of these various trees that have been inoculated with truffle mycelium. According to the September 18, 1984 issue of the Wall Street Journal, this has become a very competitive and even cut-throat business. Although, the establishment of such saplings have been very successful in parts of Europe, this was not always the case, elsewhere.
There have been numerous efforts tried to grow the host trees, with the truffle mycelium inoculated in the roots, but until recently all efforts, outside of Europe had failed. However, in 1987, New Zealand attempted to grow truffles with imported trees inoculated with T. melanosporum. In five years, the first truffles were harvested. This is half the amount of time required for plantations in France and Italy. One explanation given as to the shorter waiting period for harvesting is that New Zealand's unique flora has only a handful of species forming mycorrhizae with mushrooms - the native beeches, sometimes manuka and some ferns. The introduction of trees such as Monterey pines and Eucalyptus has increased the incidence of mycorrhizal mushroom species, but there are still many areas where such fungi are absent. It is believed that other mushroom species might compete with the black truffle but because of their absence in New Zealand, truffles do not compete with other mycorrhizal fungi for a host and other resources required for their growth. With the success in New Zealand, Australia began truffle cultivation in 1997.
An additional factor that has aided in keeping the prices for truffles high, in new Zealand is the time in which fruiting occurs. In the Norther Hemisphere, the truffles fruits from September to November. However, because New Zealand is in the Southern Hemisphere, their seasons are the reverse from ours. Thus, their truffles fruit from December to February, during our mid-winter and does not compete with the Europe's market.
In Northern California, where the climate is similar to France’s oceanic climate (mild and hardly variable), there was also once an effort to seek out native truffles. It was hoped that because the similarity in climate, that perhaps T. melanosporum, or an undiscovered native species of equal quality, would be found. Investors of this scheme even went as far as to import truffle pigs, into these areas, to sniff out the truffles. However, no truffles were ever found. Because truffles grow underground, they must be dug out. The question is, "where do you dig?" The best way to find truffles is to let pigs, and sometimes dogs, "sniff" them out. Pigs are the animals of choice, but if they are used, a choke collar is placed around its neck to prevent them from eating the truffle once they have dug them out of the ground. After digging the truffle out, the pig will invariably try to eat the truffle, but the owner will give the leash a yank and make the pig cough up the truffle.
Morels
Another, species of mushroom that has not been successfully cultivated are the morels (Fig. 29). This is another species of fungi that is highly prized, but until recently a means of cultivating it was not known. In this case, all species are edible and apparently equal in their desirability. For centuries, various methods of cultivation were tried and failed. The first report of outdoor cultivation of morels was in 1883, from France, by Roze, in association with Jerusalem artichokes. This was followed in 1904, by Molliard, who claimed to have cultivated morels in apple compost. However, there was never any evidence demonstrating that these men did actually was responsible for the morels that grew, i.e. they were believed to have arisen naturally. Some observations of specific environmental conditions, linked to fruiting of morels were tried. For example, fruiting of morels is often linked to "burned" areas, i.e. where a forest fire had occurred, or associated with Cymbidium Orchids, or paper mill sludge. However, attempts to duplicate these environmental conditions have never yielded morels. Although difficult to fruit, the mycelium of morels can easily be grown in culture, and in the early 1950’s, a great deal of effort was spent in producing mycelium, for the "essence" of morel, to be used as food flavoring. A patent was even taken out on this process, followed by a number of publications dealing with various substrates that could be used to grow the mycelium. However, this product was never as satisfying as having true morels and, with time, lost much of its appeal.
Ower (1982) published a landmark paper on the production of morel fruiting body in cultivation for Morchella esculenta (L.) Pers. Although, Ower’s paper generated a great deal of interest because he was able to repeatedly grow morels, he purposely was very vague as to the method used to grow the morel. Although, this was a big break through in the dream to cultivate morels, economically, it was not and is still not profitable because the yield was far too little to be profitable. Gary Mills, of the Neogene Corporation, in East Lansing Michigan, a Michigan State University affiliate, who recognized the potential of this process worked with Ower to try to increase the yield of the morels. After a great deal of work, in 1985, a patent was granted on the process of morel cultivation. Unfortunately, even though the process could be demonstrated, repeatedly, at the Neogene Corporation, attempts to fruit morels in the quantities necessary to make it economically feasible, have failed elsewhere. The Neogene patent was eventually sold to Terry Farms in 1994 and, by 2005 morels were being sold in Michigan and Auburn, Alabama. However, they eventually closed down operations, probably because of a low profit margin. Several other "morel growers" have also patented variations of cultivating morels. However, to date, there still does not seem to be anybody who has been able to produce them in quantities that has made it a profitable venture.
Literature Cited
Delmas, J. 1978. Growing in Caves. In S.T. Chang and W.A. Hayes (Eds.), The Biology and Cultivation of Edible Mushrooms (pp. 251-298). New York: Academic Press Inc.
Chang, S.T. 1974. Production of the straw mushroom (Volvariella volvacea) from cotton wastes. Mushroom J. 21: 348-354
Chang, S.T. 1977. Volvariella volvacea. In S.T. Chang and W.A. Hayes (Eds.), The Biology and Cultivation of Edible Mushrooms (pp. 573-603). New York: Academic Press Inc.
Chang, S.T. and P.G. Miles. Mushrooms 2004. Cultivation, Nutritional Value, Medicinal Effect, and Environmental Impact. 2nd edition. CRC Press, Boca Raton, Florida. 451 p.
Cheng, S. and C.C. Tu. 1978. Auricularia spp. In S.T. Chang and W.A. Hayes (Eds.), The Biology and Cultivation of Edible Mushrooms (pp. 605-625). New York: Academic Press Inc.
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Cultivation of Edible Mushroom Terms
Button Mushroom: Common name for A.bisporus mushroom. Most cultivated mushroom, in the world.
Casing layer: Layer of soil that covers the mycelium that has grown over the compost.
Crimini: Brown variety of A. bisporus and differs from the white button mushroom only in its brown color. It, too, is actually a button mushroom since it is harvested prior to the opening of the cap of the mushroom.
Morel: Common name given to species in the genus Morchella, in all known species are edible.
Mycoparasite: Used here to mean a fungus that is parasitic on another fungus.
Mycorrhiza: The symbiotic relationship between the roots of plants and a fungus. In the case of those involving mushroom, the relationship is obligate on the part of the mushroom. If the tree is not present which the fungus requires, the mushrooms will not be there. Sometimes the relationship is also obligate in the case of the host tree.
Oyster Mushroom: Common name for P. ostreatus, a cultivated mushroom of western origin. Species is cultivated on wood or sawdust. Cultivation of this species began only recently, during the early 20th Century.
Polypropylene bags: Heat resistant plastic bags used in the cultivation of wood decomposing mushrooms. Sawdust and a carbohydrate is mixed with water, placed in the bag and sterilized prior to inoculation of the mushroom spawn.
Portobello: Another brown variety of A. bisporus, but in this variety the mushrooms are allowed to mature and are not harvested until the cap has opened and exposed the dark brown gills.
Shiitake: Common name for cultivated mushroom, Lentinus edodes, a species that is cultivated on wood or sawdust. The mushroom is believed to be Chinese in origin and was first cultivated, in China, about 800 years ago.
Spawn: Mushroom mycelium that is inoculated into the substrate to begin cultivation of mushroom.
Truffle: Common name given to several species of Ascomycota, belonging to the genus Tuber. The species all grow underground and are associated with the roots of certain species of hard wood trees, forming a mycorrhiza. Thought to be the most prized and known to be the most expensive mushroom.
Volva: The cup-like remnant of the universal veil at the base of the stalk of certain species of mushrooms, e.g.,
Volvariella volvacea, the Paddy Straw Mushroom.
Questions to Think About
Why are so few species of mushroom cultivated?
Generally, what are the two methods by which mushrooms are mostly cultivated?
What are the two methods by which wood decomposing mushrooms are cultivated?
Tremella fuciformis cultivation requires that another fungus be grown with it. Why is this?
Why did Volvariella volvacea (Paddy Straw Mushroom) initially have such low yields when first cultivated?
How are truffles “cultivated”?
New Zealand was the first place where truffles were successfully “cultivated” outside of Europe. What reason was given as to the successful “cultivation” of truffles in New Zealand?
Gary Mills of Neogene Corporation published a paper that indicated that he and Ron Ower had perfected a method by which Morchella esculenta (morel) could be cultivated with high yields. However, when the method was repeated in other labs, the method did not work. What is this an example of?
Figure 29: Morchella esculenta
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