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date: 17 December 2017

The Cultivation and Environmental Impact of Mushrooms

Summary and Keywords

The word mushroom may mean different things to different people in different countries. Specialist studies on the value of mushrooms and their products should have a clear definition of the term mushroom. In a broad sense, “Mushroom is a distinctive fruiting body of a macrofungus, which produce spores that can be either epigeous or hypogeous and large enough to be seen with the naked eye and to be picked by hand.” Thus, mushrooms need not be members of the group Basidiomycetes, as commonly associated, nor aerial, nor fleshy, nor edible. This definition is not perfect, but it has been accepted as a workable term to estimate the number of mushrooms on Earth (approximately 16,000 species according to the rules of International Code of Nomenclature). The most cultivated mushrooms are saprophytes and are heterotrophic for carbon compounds. Even though their cells have walls, they are devoid of chlorophyll and cannot perform photosynthesis. They are also devoid of vascular xylem and phloem. Furthermore, their cell walls contain chitin, which also occurs in the exoskeleton of insects and other arthropods. They absorb O2 and release CO2. In fact, they may be functionally more closely related to animal cells than plants. However, they are sufficiently distinct both from plants and animals and belong to a separate group in the Fungi Kingdom. They rise up from lignocellulosic wastes: yet, they become bountiful and nourishing. Mushrooms can greatly benefit environmental conditions. They biosynthesize their own food from agricultural crop residues, which, like solar energy, are readily available; otherwise, their byproducts and wastes would cause health hazards. The spent compost/substrate could be used to grow other species of mushrooms, as fodder for livestock, as a soil conditioner and fertilizer, and in environmental bioremediation. The cultivation of mushrooms dates back many centuries; Auricularia auricula-judae, Lentinula edodes, and Agaricus bisporus have, for example, been cultivated since 600 ad, 1100 ad, and 1650 ad, respectively. During the last three decades, there has been a dramatic increase in the interest, popularity, and production of mushrooms through farming worldwide. The cultivation methods can involve a relatively simple farming activity, as with Volvariella volvacea and Pleurotus pulmonarius var. stechangii (=P. sajor-caju), or a high-technology industry, as with Agaricus bisporus, Flammulina velutipes, and Hypsizygus marmoreus. In each case, however, continuous production of successful crops requires both practical experience and scientific knowledge.

Mushrooms can be used as food, tonics, medicines, cosmeceuticals, and as natural biocontrol agents in plant protection with insecticidal, fungicidal, bactericidal, herbicidal, nematocidal, and antiphytoviral activities. The multidimensional nature of the global mushroom cultivation industry, its role in addressing critical issues faced by humankind, and its positive contributions are presented. Furthermore, mushrooms can serve as agents for promoting equitable economic growth in society. Since the lignocellulose wastes are available in every corner of the world, they can be properly used in the cultivation of mushrooms, and therefore could pilot a so-called white agricultural revolution in less developed countries and in the world at large. Mushrooms demonstrate a great impact on agriculture and the environment, and they have great potential for generating a great socio-economic impact in human welfare on local, national, and global levels.

Keywords: mushroom, mushroom cultivation, lignocellulose waste, mushroom industrial uses, medicinal mushrooms, dietary supplements, nutriceuticals, non-green revolution, bioremediation, environmental impact

Introduction

Mushroom cultivation is not only a source for nutritious protein-rich food, it can also contribute to the production of effective medicinal products (Chang & Wasser, 2012; Wasser, 2010, 2014). Another significant aspect of mushroom cultivation is to help reduce pollutants in the environment. The bioconversion of lignocellulosic biomass to food and useful products has had a significant impact on national and regional pollution levels and will continue to increase. (Chang, 1984; Chang & Buswell, 2003a; Koutrotsios, Mountzouris, Chatzipavlidis, & Zervakis, 2014). Bioremediation uses mushroom mycelia to remove and break down contaminants and will eventually absorb the pollutants (biosorption process), presenting another influential role of mushrooms in the ecosystem (Dai, 2016; Miller, 2013; Stamets, 2005). Cultivated mushrooms have now become popular all over the world. In 2012, the world’s total edible and medicinal mushrooms production was estimated at over 31 million tons, which was valued over 20 billion US dollars (Chang & Wasser, 2012). With no adverse legal, ethical, or safety effects, this form of bioconversion technology has not only favorable socio-economic, nutritional, and health benefits, but also raises employment possibilities (increases job opportunity) and has a positive environmental impact (Mshigeni & Chang, 2013).

What Are Mushrooms?

Mushrooms are unique, as described in the following quote:

Without leaves, without buds, without flowers, yet, they form fruit; as a food, as a tonic, as a medicine, the entire creation is precious.

(Chang & Miles, 1989)

Mushrooms are part of fungal biota characterized by wonder. Different people from different countries have different definitions of a mushroom. Because of this, no one can provide an estimation of how many mushrooms species there are on Earth. A broad use of the term mushroom embraces all large fungi, or all fungi with stalks and caps, or all large fleshy fungi. A more restricted use includes just those larger fungi that are edible and/or medicinal in value. The most extreme use of the term mushroom is in reference to just the edible species of genus Agaricus. For example, the mushroom industry in the United Kingdom and other western countries is dominated nearly 100% by A. bisporus. This could lead to the mistaken idea that this is the only species regarded as mushrooms. Some industries even consider brown mushrooms as exotic. According to mycologists, there are thousands of different species of mushrooms. These specialists classify mushrooms as a group of macro fungi, which have larger, distinctive fruiting bodies (Chang & Miles, 1992). According to the definition given by Chang and Miles (1992), a mushroom is, in a broader sense, “a macrofungus with a distinctive fruiting body. They can be either epigeous (growing above ground) or hypogenous (growing entirely in the soil), and large enough to be seen with the naked eye and to be picked by hand.” Different mushroom species may belong to one of two phylla in the sub-kingdom Dikarya (common fungi); Basidiomycetes and Ascomycetes. This is reflected in a great range of physical characteristics, including relative edibility. This definition is not a perfect one but can be accepted as a framework (Hawksworth, 2001) for estimating the number of mushrooms on Earth. The most common type of mushroom is umbrella-shaped, with a pileus (cap) and a stipe (stem), such as Lentinula edodes (Figure 1). Other species additionally have a volva (cup), Volvariella volvacea (Figure 2), or only an annulus (ring), Agarius campestris (Figure 3), or have both, as in Amanita muscaria, (Figure 4) and/or only have fruiting bodies, as in Kalahari truffle, Terfezia pfeilii (Figure 5). Furthermore, some mushrooms are in the form of pliable cups; others are round like golf balls. Some are in the shape of small clubs; some resemble coral; others are yellow or orange jelly-like globs; and some even closely resemble the human ear. In fact, their shapes and forms are countless, and their colors display all the elements of the rainbow. Their cell walls contain chitin, which also occurs in the exoskeleton of insects and other arthropods. They absorb O2 and release CO2. In fact, they may be more closely related to animal cells than plant cells (Baldauf, Roger, Wenk-Siefert, & Doolittle, 2000; Dal Campo & Ruiz-Trillo, 2013; Feeney, Dwyer, Hasler-Lewis, Milner, Noakes, Rowe, et al., 2014; Steenkamp, Wright, & Baldauf, 2006). Furthermore, mushrooms are devoid of leaves, and of chlorophyll-containing tissues. They are also devoid of vascular xylem and phloem.

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Figure 1. Lentinus edodes, a typical type of mushroom with pileus and stipe.

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Figure 2. Volvariella volvacea, with pileus, stipe, and volva.

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Figure 3. Agarius campestris, with pileus, stipe, and annulus.

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Figure 4. Amanita muscaria, with pileus, stipe, an annulus, and also the bulbous base adorned with several concentric zones of white scales representing the volva.

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Figure 5. Terfezia pfeilii, with fruiting body only.

Mushrooms are devoid of leaves, and of chlorophyll-containing tissues. They are also devoid of vascular xylem and phloem. Therefore, they are incapable of photosynthetic food production, relying instead on organic matter synthesized by surrounding green plants including organic products contained in agricultural crop residues. The organic materials on which mushrooms derive their nutrition are referred to as substrates. They process their food by secreting degrading enzymes that serve as the key to unlocking and decomposing the complex food materials present in the biomass where they grow to generate simpler compounds, which can be absorbed and then transformed into fresh new mushroom tissues. Mushrooms lack true roots but anchor themselves instead through their tightly interwoven thread-like mycelia, which colonize the substrates, degrade their biochemical components, and siphon away the hydrolyzed organic compounds for their own nutrition. These substrate materials range from decomposing material in natural ecosystems, from the soil underlying forest floors to by-products and wastes from industry, households, and agriculture.

The structure that we call a mushroom is, in reality, only the fruiting body of the fungus. The vegetative part of the fungus, called the mycelium, comprises a system of branching threads and cord-like strands—called hyphae that branch out through the soil, compost, wood logs, or other lignocellulosic material, in which the fungus may grow. After a period of growth, and under favorable conditions, the established (matured) mycelium produces the fruit structure, which we call the mushroom. In terms of human utility, mushrooms can be grouped into four categories: (a) those that are fleshy and edible fall into the edible mushroom category, such as Agaricus bisporus; (b) mushrooms considered to have medicinal applications, are referred to as medicinal mushrooms, such as Ganoderma lucidum; (c) those that are proven to be or suspected of being poisonous are named poisonous mushrooms, such as Amanita phalloides; and (d) a miscellaneous category, which includes a large number of mushrooms whose properties remain less well-defined, may tentatively be grouped together as “other mushrooms.” Certainly, this approach of classifying mushrooms is not absolute and not mutually exclusive. Many kinds of mushrooms are not only edible but also possess tonic and medicinal qualities.

Mushrooms also can be classified into various ecological groups. The most important groups are saprophytic and soil-based (living on dead organic matter), mycorrhizal (symbiotic relationship with mushroom mycelia and roots of almost all green plants), lignicolous (living on wood of trees or other substances containing lignin; some are found on living plants and are called parasitic), entomogenous (associated with insects), and coprophilous mushrooms (which grow on the dung of different animals).

Mushrooms and fungi in general are extremely abundant and diverse worldwide. Recent estimates of the number of fungi on Earth range from 500,000 to more than 5 million species, with a widely accepted working figure around 1.5 million, published 15 years ago (Hawksworth, 2001). To date, it is recommended that as many as 3 million species of fungi should be accepted (Blackwell, 2011). Meanwhile, the total number of described fungi of all kinds is currently 110,000 species. The figure is based on the total reached by adding the number of species to each genus given in the last edition of the Dictionary of Fungi (Kirk, Cannon, David, & Stalpers, 2008) and other recent publications, and includes all organisms traditionally studied by mycologists: slime molds, chromistan fungi, chytridiaceous fungi, lichen-forming fungi, filamentous fungi, molds, and yeasts. Out of these, mushrooms constitute 16,000 species, calculated from the Dictionary of Fungi and other publications of recent years (Hawksworth, 2012; Kirk et al., 2008; Wasser, 2010). But the actual number of mushroom species on Earth is currently estimated at 150,000–160,000, so only around 10% of existing mushroom species are known to science so far (Blackwell, 2011; Wasser, 2010). An analysis of the localities from which fungi new to science have been described and catalogued in the index of fungi in the last 10 years revealed that about 60% of all newly described fungi are from the tropics. This is also the case for mushrooms, especially those species forming ectomycorrhizas (symbiotic root associations) with native trees, although new species continue to be discovered in Europe and North America. In various tropical areas, 22–55% (in some cases up to 73%) of mushroom species have not yet been described (Hawksworth, 2012). Modern sequencing methods suggest that as many as 5 million species of fungi exist. Therefore, we would need more than 4,000 years to describe this fungal diversity based on the present discovery rate of about 1,200 new species per year, which has been an average for the last 10 years. Summarizing these data, we can assume that approximate 2% of world fungal biota and around 10% of world mushroom biodiversity have been discovered by mycologists to date, thus the bulk of fungal biodiversity still remains hidden.

Out of the 1.5 million estimated fungi species, Hawksworth (2012) estimated that 160,000 species produce fruiting bodies of sufficient sizes and suitable structures to be considered as macrofungi. These can be called mushrooms according to the above definition. Of the recognized mushroom species, about 7,000 species (50%) are considered to possess varying degrees of edibility, and more than 3,000 species from 231 genera are regarded as prime edible mushrooms (Wasser, 2002, 2010; Wasser & Weis, 1999). But only about 200 of the prime edible mushrooms are experimentally grown, 100 economically cultivated, around 60 commercially cultivated, and more than 10 produced on an industrial scale in many countries. Furthermore, of the 16,000 known mushroom species, approximately 700 are considered to be safe species with medicinal properties (Wasser, 2010). The number of poisonous mushrooms approximates 500 species. It should be specially emphasized that some wild unidentified mushrooms can be poisonous and lethal. Therefore, if you are not absolutely sure whether a given mushroom is edible or not, don’t touch it! Leave the unknown mushroom alone!

The Cultivation of Mushrooms

Brief History of Mushroom Cultivation

Throughout recorded history there are repeated references to the use of mushrooms as food and for medicinal purposes, and it is not surprising that the intentional cultivation of mushrooms had a very early beginning. China can boast that it was the first to successfully cultivate many popular mushrooms species—for example, Auricularia auricula-judae (estimated date, 600 ad), Flammulina velutipes (800–900 ad), Lentinula edodes (1000–1100 ad), Volvariella volvacea (1700 ad), and Tremella fuciformis (1800 ad). Prior to the 1900s, Agaricus bisporus (1650 ad in France) was the only major, commercially cultivated mushroom species that was not first cultivated in China (Chang & Miles, 2004). The extensive use of mechanized cultivation techniques for producing mushrooms in great quantities for food, like so many other large-scale agricultural activities, is a phenomenon of the 20th century. Agaricus bisporus has been a favorite mushroom in Western countries, where it is variously known as the button mushroom, the white mushroom, the cultivated mushroom, or champignon. Mushroom cultivation techniques were introduced from France to other European countries, to North America, and recently to countries throughout the world. Following World War II, there was a great spurt in the production of Agaricus, and the past few decades have also seen great increases in production of Lentinula, Flammulina, and Pleurotus and, to a lesser extent, Volvariella. (Chang & Buswell, 2008) The development of mushroom cultivation technology has been largely responsible for the increase in mushroom production. In the following section, many of the cultivation techniques are described that have been developed for different mushrooms in various parts of the world.

Principles of Mushroom Cultivation and Production

The cultivation of mushrooms ranges from a relatively primitive farming activity to a highly technological industry. In each case, however, continuous production of successful crops requires both practical experience and scientific knowledge. Mushroom cultivation is both a science and an art. The science is developed through research; the art is perfected through curiosity and practical experience. Mushroom growth dynamics involve some developmental aspects, which are in consonance with those exhibited by our common agricultural crop plants. For example, there is a vegetative growth phase, in which the mycelia grow profusely, and a reproductive (fruiting) growth phase, when the umbrella-like body that we call a mature mushroom develops. In agricultural plants such as sunflowers, when the plants switch from the vegetative growth to the reproductive growth, any further growth of the tips is retarded, and the plant is said to be mature. After the vegetative (mycelial) phase has reached maturity, what the mushroom farmer needs to do next is referred to as the induction of fruiting. This is the time mycelial growth at the tips should be slowed down and redirected by regulating specific environmental factors. These factors, generally called “triggers” or “environmental shocks,” can be switching on the light, providing fresh air, lowering temperatures, spraying the mushroom beds with water, and in some cases, reducing nutrients to trigger fruiting (Figure 6).

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Figure 6. The two major phases of mushroom growth and development: vegetative phase and reproductive phase (modified from Chang, 2001). The triggers for the transition from the vegetative phase to reproductive phase comprise the various environmental factors important for induction of fruiting. The two broken lines without labels could be nutritional factors or pH values, depending on the mushrooms cultivated.

Although the principles of cultivation are commonly similar for all mushrooms, the practical approaches can be quite different for different species cultivated. The approaches have to be modified and adjusted according to the local climatic conditions, materials available for substrates, and varieties of the mushroom used.

The Major Practical Steps of Mushroom Cultivation

Mushroom cultivation is a complex business requiring precision. Indeed, it is not as simple as what some people often loosely suppose. It calls for adherence to precise procedures. The major practical steps/segments of mushroom cultivation, as described by Chang and Chiu (1992), and Chang and Mshigeni (2013), are:

Selection of an acceptable mushroom species: Before any decision to cultivate a particular mushroom is made, it is important to determine if that species possesses organoleptic qualities acceptable to the indigenous population, or to the international market if the suitable substrates for cultivation are plentiful, and if environmental requirements for growth and fruiting can be met, without excessively costly systems of mechanical control.

Securing a good-quality fruiting culture: A “fruiting culture” is defined as a culture with the genetic capacity to form fruiting bodies under suitable growth conditions. The stock culture selected should be acceptable in terms of yield, flavor, texture, fruiting time, etc.

Development of a robust mushroom spawn: A medium through which the mycelium of a fruiting culture has grown and which serves as the inoculum of “seed” for the substrate in mushroom cultivation, is called the “mushroom spawn.” Failure to achieve a satisfactory harvest may often be traced to unsatisfactory spawn used. Consideration must also be given to the nature of the spawn substrate, since this influences rapidity of growth in the spawn medium, as well as the rate of mycelial growth and the filling of the beds following inoculation.

Preparation of selective substrate/compost: While a sterile substrate free from all competitive micro-organisms is the ideal medium for cultivating edible mushrooms, systems involving such strict hygiene are generally too costly and impractical to operate on a large scale. Substrates for cultivating edible mushrooms normally require varying degrees of pre-treatment to promote growth of the mushroom mycelia to the practical exclusion of other micro-organisms. The substrate must be rich in essential nutrients, in forms that are readily available to the mushroom, and also free of toxic substances that inhibit the growth of the spawn. Moisture content, pH, and good gas exchange between the substrate and the surrounding environment are important physical factors to consider.

Care of mycelial (spawn) running: Following composting, the substrate is placed in beds, where it is generally pasteurized by steam to kill off potential competitive microorganisms. After the compost has cooled, the spawn can either be sown over the bed surface, then pressed down firmly against the substrate to ensure good contact, or they can be inserted 2 to 2.5 cm deep into the substrate. “Spawn running” is the phase during which mycelia grow from the spawn and permeate into the substrate. Good mycelial growth is essential for mushroom production.

Fruiting/mushroom development: Under suitable environmental conditions, which may differ from those adopted for spawn running, natural germination occurs and is then followed by the production of fruiting bodies. The appearance of mushrooms normally occurs in rhythmic cycles called “flushes.”

Harvesting mushrooms carefully: Harvesting is carried out at different maturation stages, depending upon the species, and upon consumer preferences and market value.

If you ignore one critical step/segment, you are inviting trouble, which could lead to a substantially reduced mushroom crop yield and mushroom marketing value.

The Brief Background With References for Cultivation of a Few Selected Mushrooms

Mushroom cultivation involves a wide range of technologies. The choice of these technologies depends upon the species cultivated, substrates, capital available, etc. Examples of six representative mushroom species are presented here: Agaricus bisporus, Lentinula eddoes, Pleurotus pulmonarius var. stechangii, Volvariela volvacea, Agaricus brasilienesis, and Ganoderma lucidum. During the last three decades, in addition to Agaricus mushroom, many other species have been cultivated at a larger scale. In the 19th ISMS (The International Society for Mushroom Science) Congress held in the Netherlands from May 29 to June 2, 2016, it was worth noting that of the nearly 120 lectures and presentations that were submitted, approximately half concerned mushrooms other than Agaricus bisporus mushroom (Wach, 2016).

Agaricus bisporus

Agaricus bisporus (champignon, button mushroom, Figure 7) is simply the most commonly cultivated mushroom. In Western countries, cultivation of this mushroom has developed over the past 500 years, but from the onset it was considered to be a risky venture to as a predictable and controllable industrial process, particularly in France, Great Britain and the Netherlands. The culture of this mushroom originated in Paris (France) in areas in which mushrooms were frequently obtained on used compost issued from melon crops. At a later date, it was observed that this mushroom could grow without light. Therefore, its successful culture was undertaken inside caves (Delmas, 1978). France continued to lead the world as mushroom grower until the outbreak of the Second war in 1939. From that time on, the U.S. has assumed the dominant position. The mushroom-growing method in standard house was developed and adopted by the English-speaking countries. Furthermore, in western countries cultivation of Agaricus mushroom is a professional business, and for large-scare farmers it is an industrial enterprises. The improvements of cultivation techniques, for example, separating heat rooms with growing rooms, depth of beds, compost, spawn and spawning, casing, crop management, pest and disease control, harvesting etc. are not only greatly increased and stabilized the crop yield but also improved the mushroom quality. Another move was to use hybrid strains, which has enabled the growers to produce the quality mushrooms necessary for expanding domestic and export sales of fresh mushrooms. These innovative changes had to expand and to meet the changing needs of the markets. In no small measure, this remarkable achievement in modern mushroom industrial development may be attributed to contributions from vigorous research conducted at mushroom agricultural laboratories, centers, and stations. (e.g., P. B. Flegg and D. Wood, Glasshouse Crops Research Institute, Littlehampton, U.K.; G. Fritsche and L. J. Van Griensven, Mushroom Research Institute, Horst, Holland; D. J. Royse and I. C. Schisler, Department of Plant Pathology, Pennsylvania State University, Philadelphia, PA).

The specifics of this mushroom have been very well established through the repeating practical experiments of researchers like San Antonio (1975), Chang and Hayes (1978), Van Griensven (1988), Quimio, Chang, and Royse, (1990) and Kaul and Dhar (2007). The composting process for Agaricus cultivation is of particular interest here as a basic illustration of mushroom-based agriculture (Buth, 2016; Hayes, 1977; Hilkens, 2016; Nair, 1993).

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Figure 7. Agaricus mushrooms grown on horse manure compost.

Generally, composting refers to the piling up of substrates for a certain period of time and the changes due to the activities of various microorganisms, which result in the composted substrate becoming chemically and physically different from the starting material. This is sometimes referred to as a solid-state fermentation. Two types of composting are commonly described. One type involves the decomposition of heaps of organic wastes and the subsequent application of the residue to the soil. The aim of this type of composting is to reduce, in a sanitary manner, both the volume and the carbon and nitrogen ratio of the organic waste so that is it suitable for manuring the soil to improve the growth of plant crops. When given directly to the soil without composting, organic waste with a high C:N ratio (such as straw) can give rise to a temporary nitrogen deficiency, which will then result in a reduction in yield of the plant crop.

The role of second type of composting is the production of a selective substrate that will preferentially support the growth of the mycelium of the mushroom. The basis of this selectivity, however, cannot be attributed to one factor or one aspect of the entire system. The physical, chemical, and biological aspects of composting are fundamentally interrelated, but can be artificially separated for the convenience of investigation and discussion.

Mushroom growers use their sense of sight, smell, and touch to evaluate the progression of the composting process and the quality of the final product. The gross characteristics of compost, usually referred to as “structure,” result from a number of complex physical, chemical, and microbial processes that comprise composting (Nair, 1993).

Composting is prepared in accordance with well-documented commercial procedures (Chang & Hayes, 1978; Kaul & Dhar, 2007; Van Griensven, 1988). In Phase I of the process (outdoor composting), locally available raw materials are arranged into piles, which are periodically turned and watered. The initial breakdown of the raw ingredients by microorganisms takes place in Phase I. This phase is usually complete within 9 to 12 days, when the materials have become pliable, dark brown in color, and capable of holding water. There is normally a strong smell of ammonia. The aeration—a good supply of oxygen—has been recognized recently to be significantly important in phase I compost (Buth, 2016). Phase II (indoor fermentation) is pasteurization, when undesirable organisms are removed from the compost. This is carried out in a steaming room where the air temperature is held at 60 °C for at least 4 hours. The temperature is then lowered to 50 °C for 8 to 72 hours, depending upon the nature of the compost. CO2 is maintained at 1.5 to 2%, and the ammonia level drops below 10 PPM. Following Phase II composting, the substrate is cooled to 30 °C for A. bitorquis and to 25 °C for A. bisporus for spawning. Production of Phase III or Phase IV composts for growing Agaricus mushrooms has been an advanced technological development in recent years in Western countries. The production of Phase III compost is Phase II compost spawn run in a bulk tunnel, and ready for casing when delivered to the grower. If the Phase III compost is then cased, and spawn develops into a casing layer before dispatching to the growing unit or delivering to growers, it is named as Phase IV compost. The successes of bulk Phase III and Phase IV depend a lot on the quality of Phase I and Phase II processes.

Phase II composting undertaken on shelves produces an average of 4.1 crops per year. Since 1999, growers using Phase III production have enjoyed an average of 7.1 crops per year. In recent years, Phase IV can generate 10–12 crops per year (Dewhurst, 2002; Lemmers, 2003). So, good compost is vital for supporting cultivation and represents 85% of the power behind mushroom production (Heythuysen, 2015).

Lentinula edodes

Lentinula edodes (Xiang-gu, shiitake, oak mushroom, Figure 8) is one of the most important edible mushrooms in the world from the standpoint of production, and it is the most popular fungus cultivated in China, Japan, and in some other Asian countries. For a long time, this mushroom has been valued for its unique taste and flavor and as a medicinal tonic. It can be cultivated either on wood log or on synthetic substrate logs (Chang & Miles, 2004; Quimio et al., 1990; Stamets, 2000).

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Figure 8. Lentinula edodes grown on sawdust synthetic logs.

Lentinula edodes is a kind of wood rot fungus. In nature, it grows on dead tree trunks or stumps. In general, the wood for the mushroom growth consists of crude protein, 0.38%; fat, 4.5%; soluble sugar, 0.56%; total nitrogen, 0.148%; cellulose, 52.7%; lignin, 18.09%; and ash, 0.56%. Generally speaking, the C/N in substrate should be in the range from 25 to 40:1 in the vegetative growth stage and from 40 to 73:1 in the reproductive stage. If the nitrogen source is too rich in the reproductive phase, fruiting bodies of the mushroom are usually not formed and developed.

The optimum temperature of spore germination is 22–26 ºC. The temperature for mycelial growth ranges from 5–35 ºC, but the optimum temperature is 23–25 ºC. Generally speaking, L. edodes belongs to low temperature mushrooms, the initial and development temperature of fruiting body formation is in the range of 10–20 ºC, and the optimum temperature of fructification for most varieties of the mushroom is about 15 ºC. Some varieties can fruit in higher temperatures, 20–23 ºC. These high temperature mushrooms usually grow faster and have a bigger and thinner cap (pileus), and a thin and long stalk (stipe). Their fruiting bodies are easily opened and become flat grade mushrooms, which are considered to be low quality. The optimum pH of the substrate used in making the mushroom bag/log is about 5.0–5.5 (Chang & Miles, 2004; Stamets, 2000).

Culture media and preparation: The mushroom can grow on a variety of culture media and on different agar formulations, both natural and synthetic, depending on the purpose of the cultivation. Synthetic media are often expensive and time-consuming in preparation; hence they are not commonly used for routine purposes.

The potato dextrose agar, or PDA, is the simplest and the most popular medium for growing the mycelium of the mushroom. It is prepared as follows:

Ingredients: Diced potato 200 gm; dextrose (or ordinary white cane sugar), 20 gm; powdered agar (or agar bars), 20 gm; and distilled water (or tap water) 1 liter.

Procedure: Peeled potatoes are washed, weighed, and cut into cubes. They are boiled in a casserole with at least one liter of water until they become soft (around 15 minutes). The potatoes are removed and water is added to the broth to make exactly 1 liter. The broth is returned to the casserole, and dextrose and the agar added. The solution is heated and stirred occasionally until the agar is melted. The hot solution is then poured into clean flat bottles. For pure or stock cultures, the test tubes are filled with at least 10 ml of the liquid agar solution. The bottles or test tubes are plugged with cotton wool. When Petri dishes are available, these can be used to produce mycelial plugs for inoculation of mother spawn.

The L. edodes mushroom is produced on both cottage and commercial scale. The following section outlines some of the issues associated with the different cultivation styles.

Cottage scale cultivation: There are many formulas for the composition of the substrate. The ingredients can vary from place to place and country to country depending upon the raw materials available and local climatic conditions. In general, after mixing the dry ingredients by hand or with a mechanical mixer, water is added to the mixture so that the final moisture content of the substrate is between 55 and 60%, depending on the capacity of the sawdust to absorb water. The ingredients are then packed into autoclavable polypropylene or high-density polyethylene bags. Although they are more expensive, polypropylene bags are the most popular since polypropylene provides greater clarity than polyethylene. After the bags have been filled (1.5 to 4 kg wet wt.) with the substrate, the end of the bag can be closed either by strings or plugged with cotton wool stopper. Four formulas in the preparation of the substrate for the cultivation of the mushroom are given here as reference: (a) Sawdust 82%, wheat bran 16%, gypsum 1.4%, potassium phosphate, dibasic 0.2%, and lime 0.4%; (b) Sawdust 54%, spent coffee grounds 30%, wheat bran 15%, and gypsum 1%; (c) Sawdust 63%, corncob powder 20%, wheat bran 15%, calcium superphosphate 1%, and gypsum 1%; (d) Sawdust 76%, wheat bran 18%, corn powder 2%, gypsum 2%, sugar 1.2%, calcium superphosphate 0.5%, and urea 0.3%.

Commercial scale cultivation: In general, the operation can use oak or other hard wood sawdust medium to grow the mushroom. The basic steps are (a) to mix the sawdust, supplements, and water; (b) bag the mixture; (c) autoclave the bags to 121 ºC and cool the bags; (d) inoculate and seal the bags; (e) incubate for 90 days to achieve full colonization of the sawdust mixture, in other words, to allow the mycelium be established for ready fructification; (f) fruit the colonized and established sawdust logs/bags/blocks 6 times using a 21 days cycle at 16 to 18 ºC; and (g) harvest, clip steps, grade, box, and cold store for fresh market, or harvest, dry, cut steps, grade, and dry again before box for dry market.

Major equipment used in production consists of mixer/conveyor, autoclave, gas boiler, cooling tunnel, laminar-flow cabinet, bag sealer, air compressor for humidification, shelves to incubate.

Incubation can be done in two rooms and in two shipping containers. The two shipping containers can be installed near the fruiting rooms. Temperature during incubation is held between 18 and 25 ºC.

Fruiting can be done in six rooms so that the blocks/logs can be moved as a unit. With compartmentalization, blocks in each room can be subjected to a cycle of humid cold, humid heat, and dry heat.

Pleurotus pulmonarius var. stechangii

Pleurotus pulmonarius var. stechangii (=P. sajor-caju) (Chang’s oyster mushroom) is comparable to the high temperature species in the group of Pleurotus (oyster) mushrooms, with high temperatures required for fructification. This mushroom has a promising prospect in tropical and subtropical areas. Its cultivation is easy with relatively less complicated procedures (Chang & Miles, 2004; Kaul & Dhar, 2007; Zmitrovich & Wasser, 2016, Figure 9).

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Figure 9. Pleurotus pulmonarius var. stechangii grown on cereal straw substrate.

The temperature for growth of mycelium is 10–35 ºC. The optimum growing temperature of the mycelium is 23–28 ºC. The optimum developmental temperature of the fruiting body is 18–24 ºC. The optimum pH of the substrate used in making the mushroom bag/bed is 6.8–8.0. The C/N ratio in the substrate is in the range of 30–60:1. A large circulation of air and reasonable light are required for the development of the fruiting bodies.

Spawn substrate: (a) Wheat grain + 1.5% gypsum or lime; (b) Cotton seed hull, 88%; wheat bran, 10%; sugar, 1%; and gypsum, 1%; (c) Sawdust, 78%; wheat bran, 20%; sugar, 1%; and gypsum, 1%; (d) Sawdust, 58%; spent coffee grounds/spent tea leaves, 20%; water hyacinth/cereal straw, 20%; sugar, 1%; and gypsum, 1%.

Cultivation substrate: (a) Cotton seed hull, 95%; gypsum, 2%; lime, 1%; and calcium superphosphate, 2%; (b) Rice straw, 80%; cotton waste, 18%; gypsum, 1%; and lime, 1%; (c) Water hyacinth, 80%; cereal straw; 17%, gypsum, 2%; and lime, 1%.

For demonstration purpose, this mushroom can be nurtured to grow into a tree-like shape (Figure 10). The cultivation method, which has been tested successfully, is as follows: Cotton waste or rice straw mixed with water hyacinth is used as the substrate. Tear large pieces of cotton waste into small parts or cut the straw and water hyacinth into small segments. Add 2 % (w/w) lime and mix with sufficient water to get moisture content of about 60–65%. Pile the materials up, cover with plastic sheets, and leave to stand overnight. Load the substrate into small baskets or onto shelves for pasteurization, or cook the substrate with boiled water for 15 minutes. After cooling to approximately 25 ºC, mix around 2% (w/w) spawn thoroughly with the substrate and pack into columns of 60-cm-long tubes that have hard plastic (PVC) tubing of 100 cm (4 cm in diameter) as central support, and plastic sheets as outside wrapping (Chang, Lau, & Cho, 1981).

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Figure 10. Robust growth of Pleurotus pulmonarius var. stechangii as a mushroom tree.

Incubate these columns at around 24 to 28 ºC, preferably in the dark. When the mycelium of the mushroom has ramified the entire column of substrate after three to four weeks, remove the plastic wrapping and switch on white light. Watering is needed occasionally, to keep the surface from drying. In around three to four days, white primordia start to appear over the whole surface. After another two to three days, the Pleurotus mushrooms are ready for harvesting. During the cropping period, watering is very important if many flushes are required.

Volvariella volvacea

Volvariella volvacea (patty straw mushroom, Chinese mushroom, Figure 11) is a fungus of the tropics and subtropics and has been traditionally cultivated in rice straw for many years in China and in Southeast Asian countries (Chang, 1965). In 1971, cotton wastes were first introduced as heating material for growing the straw mushroom (Yau & Chang, 1972). In 1973, cotton wastes had completely replaced the traditional paddy straw for growing mushrooms (Chang, 1974). This was a turning point in the history of straw mushroom cultivation because the cotton waste compost through the pasteurization process brought the cultivation of the mushroom to an industrial scale—first in Hong Kong and then in Taiwan, Thailand, and China. Several techniques are adopted for the cultivation of the mushroom, which thrives in temperature ranges of 28 to 36 ºC and a relative humidity of 75–85%. Detailed descriptions of the various methods are given by Chang and Miles (2004), Kaul and Dhar (2007), and Quimio et al. (1990). Choice of technologies usually depends on personal preference, on the availability of substrates, and the amount of resources available. While more sophisticated indoor technology is recommended for industrial-scale production of the mushroom, most other technologies are low-cost and appropriate for rural area development, especially when production is established at the community level.

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Figure 11. Different stages of fruiting bodies of the straw mushroom (Volvariella volvacea) grown on cotton waste as substrate

Agaricus brasiliensis

In recent years, A. brasiliensis (Royal Sun Agaricus, Himematuatake, Figure 12), formerly called A. blazei Murrill (Wasser, Didukh, Amazonas, Nevo, Stamets, & da Eira, 2002) has rapidly become a popular mushroom. It has been proved to be not only a good tasting and highly nutritious mushroom, but also an effective medicinal mushroom, particularly for anti-tumor active polysaccharides.

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Figure 12. Different stages of Agaricus brasiliensis mushroom grown in straw compost with case soil.

A. brasiliensis originated as a wild mushroom in south eastern Brazil, where it was consumed by the people as a part of their diet. The culture of the mushroom was brought to Japan in 1965, and an attempt to cultivate this mushroom commercially was made in 1978. In 1992, this mushroom was introduced to China for commercial cultivation (Chang & Miles, 2004).

A. brasiliensis belongs to the so-called “middle temperature mushrooms.” The growth temperature for mycelium ranges from 15 to 35 ºC and the optimum growth temperature ranges from 23 ºC to 27 ºC. The temperature for fruiting can be from 16 ºC to 30 ºC, and the optimum developmental temperature of fruiting bodies is 18 ºC to 25 ºC. The ideal humidity for casing soil is 60–65%. The air humidity in a mushroom house prefers 60–75% for mycelium growth and 70–85% for fruiting body formation and development. The optimum pH of the compost used in making the mushroom bed is 6.5–6.8. The optimum pH of the casing soil is 7.0. A good circulation of air is required for the development of the fruiting bodies. These conditions are similar to those needed for the cultivation of A. bisporus. Under natural conditions, the mushroom can be cultivated for two crops each year. Each crop can harvest three flushes. According to the local climates, the farmer can decide the spawning time in the year in order to have mushrooms for harvest within 50 days after spawning.

Preparation of mushroom bed (Stamets, 2000): A. brasiliensis is a kind of mushroom belonging to the straw-dung fungi and prefers to grow on substrate rich in cellulose. The waste/by-productive agro-industrial materials, such as rice straw, wheat straw, bagasse (squeezed residue of sugar cane), cotton seed hull, corn stalks, sorghum stalk, and even wild grasses, can be used as the principal component of the compost for cultivation of the mushroom. It should be noted that these materials have to be air dried first and then mixed with cattle dung, poultry manure, and some chemical fertilizers. The following formulas for making compost are for reference only. They should be modified according to the local available materials and climatic conditions: (a) Rice straw, 70%; air-dry cattle dung, 15%; cottonseed hull, 12.5%; gypsum, 1%; calcium superphosphate, 1%; and urea, 0.5%; (b) Corn stalks, 36%; cottonseed hull, 36%; wheat straw, 11.5%; dry chicken manure, 15%; calcium carbonate, 1%; and ammonium sulphate or urea, 0.5%; (c) Rice straw, 90.6%; rice bran, 2.4%; fowl droppings, 3.6%; slaked lime, 1.9%; superphosphate, 1.2%; and ammonium sulphate/urea, 0.3%; (d) Bagasse, 75%; cottonseed hull, 13%; fowl droppings, 10%; superphosphate, 0.5%; and slaked lime, 1.5%.

Ganoderma lucidum

Although the medicinal value of G. lucidum (lingzhi, Reishi, Figure 13) has been treasured in China for more than two thousand years, the mushroom was found infrequently in nature. This lack of availability was largely responsible for the mushroom being so highly cherished and expensive. During ancient times in China, any person who picked the mushroom from the natural environment and presented it to a high-ranking official was usually well rewarded (Chang & Miles, 2004).

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Figure 13. The fruiting bodies of Ganoderma lucidum grown on short-wood segments that were then buried in the soil base for fruiting.

Artificial cultivation of this valuable mushroom was successfully achieved in the early 1970s and, since 1980 and particularly in China, production of G. lucidum has developed rapidly. Currently, the methods most widely adopted for commercial production are the wood log, short wood segment, tree stump, sawdust bag, and bottle procedures (Chang & Buswell, 1999; Stamets, 2000; Hsu, 1994; Mizuno et al., 1995).

Log cultivation methods include the use of natural logs and tree stumps, which are inoculated with spawn directly under natural conditions. The third alternative technique involves the use of sterilized short logs, about 12 cm in diameter and approximately 15 cm long, which allow for good mycelial running. This method provides for a short growing cycle, higher biological efficiency, good quality of fruiting bodies, and consequently, superior economic benefit. However, this production procedure is more complex and the production costs much higher than natural log and tree stump methods. For this production procedure, the wood logs should be prepared from broad-leaf trees, preferably from oak. Felling of the trees is usually carried out during the dormant period, which is after defoliation in autumn and prior to the emergence of new leaves the following spring. The optimum moisture content of the log is about 45–55% .The flow-routine for the short-log cultivation method is as follows: selection and felling of the tree; sawing/cutting the log into short segments; transference of segments to plastic bags; sterilization; inoculation; spawn running; burial of the log in soil; tending the fruiting bodies during development from the pinhead stage to maturity; harvesting of the fruiting bodies; drying of the fruiting bodies by electrical driers; packaging. It should be noted that the prepared logs/segments are usually buried in soil inside a greenhouse or plastic shed. The soil should allow optimum conditions of drainage, air permeability, and water retention, but excessive humidity should be avoided.

Examples of cultivation substrates, using plastic bags or bottles as containers, include the following (please note that these examples are for reference purposes only and can be modified according to the strains selected and the materials available in different localities): (a) Sawdust, 78%; wheat bran, 20%; gypsum, 1%; and soybean powder, 1%; (b) Bagasse, 75%; wheat bran, 22%; cane sugar, 1%; gypsum, 1%; and soybean powder, 1%; (c) Cotton seed hull, 88%; wheat bran, 10%; cane sugar, 1%; and gypsum, 1%; (d) Sawdust, 70%; corn cob powder, 14%; wheat bran, 14%; gypsum, 1%; and cereal straw ash, 1%; (e) Corn cob powder, 78%; wheat/rice bran, 20%; gypsum, 1%; and straw ash, 1%. After sterilization, the plastic bags can be laid horizontally on beds or the ground for fruiting.

Rapid Expansion of the Mushroom Industry in the Late 20th Century

It has been noted that a nutritious balance of foods and an active lifestyle under a friendly environment can help achieve optimal health throughout life. The use of mushrooms as diet therapy to sustain or improve health or treat illness was used by ordinary people and in the imperial court of China as far back as 2,000 years ago (Xue & O’Brien, 2003). The pyramidal model of mushroom uses (Figure 14) conforms fully to an old Chinese saying “Medicine and food have a common origin.” This statement is particularly applicable to mushrooms, whose nutritional qualities and tonic effects as nutriceuticals (Chang & Buswell, 1996) or as dietary supplements (DSs) and medicinal attributes have long been recognized (Wasser, 2010). Human health may be divided into three states: health, sub-health, and illness. Mushrooms can be used mainly as food for a healthy state, as a medicine for illnesses, and as DSs for a sub-healthy state, as well as for both healthy and ill states (Chang & Wasser, 2012).

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Figure 14. A pyramid model of mushroom uses (industry), Source: Chang and Wasser (2012).

Since the end of World War II, mushroom production has increased steadily in agricultural-based industries. World production of cultivated edible mushrooms over a number of years is shown in Table 1. In 1981, production totaled 1,257.2 thousand tons and in 1986, 2,182.0 thousand tons, a 73.6% increase. By 1990, total production was 3,763.0 thousand tons, increasing to 6,158.4 thousand tons by 1997. Overall, world mushroom production increased over 12% annually during the period from 1981 to 1997. However, the Agaricus mushrooms decreased in percentage of world total production. This is mainly due to other alternative edible mushrooms becoming more in demand; for instance, Lentinus edodes increased in percentage of total global mushroom consumption, from 14.3% in 1981 to 25.2% in 1997, and in production, from 180 thousand tons to 1,564.4 thousand tons. Pleurotus mushrooms increased from 2.8% to 14.2%, and their production increased from 35 thousand tons to 875.6 thousand tons, with a 25-fold increase over the same period of time. Auricularia mushrooms increased from 0.8% in 1981 to 7.9% in 1997, and their production increased from 10,000 thousand tons in 1981 to 485.6 thousand tons in 1997, with a 48.5-fold increase (Chang & Wasser, 2012). Overall, increase in world mushroom production has been due mainly to contributions from countries with developing economies including China, India, Poland, and Hungary. In contrast, mushroom production in Western European countries, the United States, and Japan, has remained unchanged or has even fallen. China especially has witnessed a huge increase in edible mushroom cultivation and now makes the largest contribution, by over 85%, to the total worldwide output (Table 2). Furthermore, several new species of mushrooms have been recently cultivated and marketed in China. India’s annual production of mushrooms doubled, from 5,000 tons in 2001 to 10,000 tons in 2004, and is expected to continue rising, at about 25% per annum, for the foreseeable future. In Latin America, the annual mushroom production has also increased steadily since 1995. During the period 1995–2001, the estimated commercial mushroom production level in this region rose by 32% (49,975 to 65,951 tons), equivalent to an annual increase of 5%. Since mushroom cultivation can be a labor-intensive agro-industrial activity, it could have great economic and social impact by generating income and employment for both women and youth, particularly in rural areas in developing countries. Using China as an example, in 1978 the total production of mushrooms in China was only 60 thousand tons, which accounted for less than 6% of total world mushroom production. In 2012 (Table 2), however, total production of mushrooms in China reached 28.3 million tons, which accounted for more than 85%. In 2013 (Royse, Baars, & Tan, 2017), world production of cultivated edible mushrooms has increased to 34 million tonnes. China is the main producer of mushrooms, producing over 30 million tons. This is accounted for about 87% of total production. The rest of Asia produced about 1.3 million tons, while the European Union, the Americas, and other countries produced about 3.1 million tons. In the same report, Lentinula edodes is the major species, contributing about 22% of the world’s cultivated mushrooms. Pleurotus spp, including 5 to 6 cultivated species, contributes about 19%, and Auricularia spp, including 2 to 3 species, contributes 17%, while Agaricus bisporus mushroom is responsible for 15% of the volume. Moreover, according to Feeney et al. (2014), since 2009, China has produced 65% of global mushrooms and truffles, the European Union 24%, the United States 5%, and Japan, Indonesia, and Canada 1% each. Exact figures of world production of mushrooms are actually difficult to obtain, because some estimated figures are the total weight of all kinds of mushroom products including the fresh, dried, and canned. That is incorrect. Technically, however the dried, canned, and other preserved products should first be converted to equivalent fresh weight and then added together.

Table 1. World Production of Cultivated Edible Mushrooms, Fresh Equivalent, from 1960–2009

Year

Production (x 1,000 MT)

Increase, %

Annual Increase. %

1960

170.0

1965

341.0

100.6

20.1

1970

546.0

60.0

12.0

1975

916.0

67.8

13.6

1981

1,257.2

37.3

6.2

1986

2,176.0

73.1

14.6

1990

3,794.0

74.4

18.6

1991

4,273.0

12.6

12.6

1994

4,909.3

14.9

5.0

1997

6,158.4

25.4

8.5

2002

12,250.0

98.9

19.8

2009

24,000.0

95.9

13.7

2012

31,500.0

31.3

10.4

Annual average increase 12.9

Note:

(*) This figure assumes that the Chinese contribution was 28,280 million tons in 2012 (China Edible Fungus Association, 2012, 2014). The rest comprised all other countries.

Sources: Chang (1999a), Delcaire (1978), and Sharma (1997).

Table 2. China’s Contribution to Worldwide Mushroom Production Since 1978

Year

Total production (x 1,000 tons)

China’s production (x1,000 tons)

China’s contribution (%)

1978

1,060.0

60.0

5.7

1983

1,453.0

174.5

12.0

1990

3,763.0

1,083.0

28.8

1994

4,909.3

2,640.0

53.8

1997

6,158.4

3,918.0

63.6

2002

12,250.0

8,650.0

70.6

2006

NA

14,000.0

NA

2009

24,000.0

20,200.0

More than 80

2012

31,500.0

28,280.0

More than 85

2014

NA

32,700.0

NA

Note: NA, not available.

Sources: Chang (1991, 1999b), and Huang (2000); and China Edible Fungus Association (2012, 2014).

Total employment in the mushroom industry in China was over 35 million people in 2012, with only 15% employed as actual mushroom farmers; other employment categories were in sectors such as food, beverage manufacturing, trading and management, transport, marketing, wholesaling, retailing, export, etc. The mushroom industry can also have even a broader positive spillover, generating complementary employment in areas such as accommodation, restaurant services, etc. Furthermore, it is interesting to note that in some counties in China (e.g., Qingyuan, in Zhejiang province in 1997 with a population of just under 200,000 people), 60% of the populations were engaged in mushroom production and management (Chang, 2006). The local mushroom industry can also be the main source of revenue for local government. The development of the mushroom industry in China, for example, can be used as a model for other less-developed countries.

The call for a “non-green” or “white revolution” in the 21st century (Chang, 1999a) began with the conviction that mushrooms, increasingly, are being realized as an invaluable treasure, with vital roles in many facets of human welfare. They have multi-beneficial effects, as food, health tonic, and medicine, as well as for feed, fertilizers, and as environmental protection services. The global impact of edible and medicinal mushrooms on food, environment, social change, economic growth, and quality of health is expected to continue increasing and expanding in the 21st century because, on average, more than 70% of agricultural and forest materials are non-productive (Pauli, 1996) and have been treated as lignocellulosic wastes in processing. Therefore, sustainable research and the development of mushroom-based biotechnological industries have been named as the “non-green revolution” or “white agricultural revolution.” Mushrooms and their multi-beneficial products should not be considered a luxury for only certain segments of the population, but rather as a national, regional, and global necessity for all people. It should be emphasized that good quality and honest products for mushroom crops are of paramount importance in earning enduring public credibility and securing an expanding market in the future (Chang, 1999b).

The Environmental Significance of Mushroom Cultivation

Technologies and innovations for human development are expanding every day. However, our world’s inhabitants, particularly in some less developed countries, still face, and will continue to face, three basic problems (Chang & Wasser, 2012): (a) inadequate food supplies, (b) diminishing quality of health, and (c) increasing environmental deterioration. These three key underlying problems will affect the future wellbeing of humankind. The magnitude of these problems is set to increase as the world’s population continues to grow. The 20th century began with a world population of 1.6 billion and ended with 6.0 billion inhabitants. According to the report UN World Population Prospects (2015), the world population reached 7.3 billion as of mid-2015. It is expected to reach 8.5 billion by 2030, 9.7 billion in 2050, and 11.2 billion in 2100 with most of the growth occurring in less-developed countries. With the population still growing by about 80 million each year, it is hard not to be alarmed. Inevitably, the amount of food and the level of medical care available to each individual will decrease, and global ecosystems will be subjected to intensified abuse.

The commonly used Ehrlich equation in the environmental field calculates environmental impact by considering the combination of three principle factors, namely, population, affluence (consumption per person), and technology (I = P x A x T). In promoting mushroom cultivation in this article, we would like to emphasize the importance of bioconversion and bioremediation technologies as a factor in transforming the factor (T).

Reducing Environmental Pollution Through Bioconversion of Vast Quantities of Organic Wastes into Mushrooms

Organic solid wastes are a kind of biomass, which are generated annually through the activities of the agricultural, forest and food processing industries. They consist mainly of three components: cellulose, hemicellulose, and lignin. The general term of these three main building blocks of plant fiber is known as lignocellulose (Chang, 1987, 1989). These are organic compounds composed of long chains of carbon and hydrogen, structurally similar to many organic pollutants. It is common knowledge that lignocellulosic wastes are available in abundance both in rural and urban areas. They have insignificant or less commercial value and certainly no food value, at least in their original form. When carelessly disposed of in the surrounding environment by dumping or burning, these wastes are bound to lead to environmental pollution and, consequently, to health hazards (Stamets, 2005). These wastes can be converted into valuable resources through proper management, with their utilization leading to reduced environmental pollution and further economic growth.

Lignocellulosic compounds are complex and insoluble. They can be treated by various chemical methods, for example, with dilute hydrochloric acid and calcium chloride to increase the digestibility and nutritional qualities, and even to form sugars to serve as carbon sources. However, these chemical methods are tedious and costly. Furthermore, treatments to eliminate adverse side effects of the chemicals are also very complex. In contrast, mushroom cultivation techniques have become significantly important in recent years to improve nutritional quality and to upgrade the economic value of the solid organic wastes. Mushrooms, with other fungi, are presently only organisms that can synthesize and excrete the relevant hydrolytic and oxidative enzymes that enable them to degrade complex organic substrates into soluble substances, which can then be absorbed by the mushrooms for their nutrients (Chang & Miles, 2004). Different species of mushrooms have different abilities to utilize the substrates. This depends on the particular enzymes secreted by the individual mushroom. Examining the lignocellulolytic enzyme profiles of three important commercially cultivated mushrooms exhibit varying abilities to utilize different lignocellulolytic as growth substrate (Buswell & Chang, 1994; Buswell, Cai, Chang, Peberdy, Fu, & Yu, 1996): (a) Lentinula edodes, cultivated on highly lignified substrates, such as wood or sawdust, produces two extracellular enzymes (manganese perxidase and laccase), which have been associated with lignin depolymerization. (b) Conversely, Volvariella volvacea prefers high-cellulose, low lignin-containing substrates, such as paddy straw and cotton wastes, which have relatively low-lignin content, and it produces a family of cellulolytic enzymes including at least five endoglucanases, five cellobihydralases, and two ß-glucosidases, but none of the recognized lignin-degrading enzymes. (c) Pleurotus pulmonarius var. stechangii (an oyster mushroom) is the most adaptable of the three species and can be grown on a wide variety of agricultural waste materials of differing composition in terms of polysaccharide/lignin ration, because it can excrete both kinds of cellulose- and lignin-degrading enzymes.

Recycling of Organic Wastes into Mushrooms, Biogas, and Biofertilizer

The ultimate aim in the applied aspects of any scientific endeavor is to integrate wherever possible the various disciplines of science as well as the technological processes, to maximize benefits accrued from such efforts. Combined production of mushrooms, biogas, and biofertilizer from rural and urban organic wastes should be one of the aims of such integrated schemes that can eventually be put into profitable and beneficial operation. Through the conventional and established methods of food production, the explosive growth of the population vis-à-vis the rapid depletion of conventional fuel resources leads people to look for alternative sources for food, fertilizer, and fuel.

Even though people have been harvesting mushrooms as food from wild sources from time immemorial, their nutritive value was not assessed, and their production under controlled conditions was, for the most part, not undertaken until recent decades. The lignocellulosic substrate, used for mushroom production after harvesting the mushrooms, is used as compost for soil conditioning or organic fertilizer. It should be noted that this compost, besides being rich in nitrogenous material, contains partly degraded lignocellulosic components that, when combined with pure animal dung or human excrement in a biogas digester, yields not only biogas but is also a good quality organic nitrogenous fertilizer in the form of sludge. The sludge from the biogas plant as a nitrogenous fertilizer is far more beneficial than the compost from which it has been derived. Part of the biogas that is produced in the vicinity of the mushroom house can also be conveniently used for pasteurization of the mushroom bed material and maintenance of the optimal temperature in the house as well. It is therefore suggested that an integrated approach in the production of mushroom, biogas, and biofertilizer should be considered as a feasible approach for rural and urban lignocellulosic waste utilization and disposal. This approach is in line with the “Zero Emission or Total Productivity” concept, derived from A Report on ZERI (Zero Emissions Research Initiative) by Hablutzel (2010). The philosophy of this increasingly popular perspective is summarized by the statement “We cannot expect the Earth to produce more—we have to do more with what the Earth already produces.”

Restoration of a Damaged Environment by Mushroom Mycelium

One of the primary roles of mushrooms in the ecosystem is decomposition, which is performed by the mycelium. Mushroom mycelium can produce a group of complex extracellular enzymes, which can degrade and utilize the lignocellulosic wastes to reduce pollution. Mushroom mycelia can also play a significant role in the restoration of damaged environments. Stamets (2005) has coined a term, mycorestoration, which can be performed in four different ways: mycofiltration (using mycelia to filter toxic waste and microorganisms from water in soil film in the air), mycoforestry (using mycelia to restore forests), mycoremediation (a form of bioremediation using mycelia to decontaminate the area), and mycopesticides (using mycelia to control insect pests). These methods represent the potential to create a clean ecosystem, where no damage will be left after fungal implementation, even if there are some toxic wastes. Bioremediation is a very important technique that involves the use of mushroom mycelia to remove or neutralize a wide variety of pollutants (Kulshreshtha, Mathur, & Bhatnagar, 2013; Purnomo, Mori, Putra, & Kondo, 2013). In order to clean contaminated land, various examples include: spent oyster mushroom substrate performing better than many mushrooms for denaturing of biocide pentrachlorophenol (Chiu, Ching, Fong, & Moore, 1998); removal of biocide pentachlorophenol in water systems using the spent mushroom compost of Pleurotus pulmonarius (Law, Wai, Lau, Lo, & Chiu, 2003); use of spent mushroom compost to bioremediate PAH-contaminated samples (Lau, Tsang, & Chiu, 2003); mycoremediation (bioremediation with fungi)—growing mushrooms to clean the earth (Rhodes, 2014); removal of Escherichia coli from synthetic storm water using mycofiltration (Taylor, Flatt, Beutel, Wolff, Brownson, & Stamets, 2015). In addition, Stamets (2005) provides some excellent examples.

Economic and Social Impacts

It has been estimated (Pauli, 1996) that over 70% of agricultural and forest crop biomass produced is conceived as unusable materials and discarded as wastes/by-products that are not edible. Here are some examples: the extracted fiber constitutes only 2% of the sisal plant, and the remaining 98% is thrown away as waste; cane sugar represents a mere 17% of the weight of the biomass of the plant, while the remaining 83% is discarded as bagasse; extracted oil represents only 5% of the total biomass generated by palm coconut plantations, and 95% is waste; and trees are logged throughout the world, mainly to extract the cellulose in timber, which represents only about 30% of the biomass in the case of hardwood and a mere 20% in the case of softwoods. In addition, billions of tons of sawdust, wood chip, coffee pulp, spent ground coffee, brewery spent grain, cotton seed hull, textile cotton waste, and cereal straw around the world are discarded as waste. The main disposal methods of these materials include burning on site, burying, and dumping at unplanned and uncontrolled landfills. Thereby, they may serve to pollute the environment in some cases if they are not properly treated. Actually, these lignocellulosic biomass waste materials are potential raw substrates for cultivation of both edible and medicinal mushrooms, which are beneficial to human welfare as mentioned above. The following statements summarize the significance of mushrooms in our drive towards alleviating poverty, enhancing human health, and arresting environmental degradation: (a) Mushrooms can convert lignocellulosic waste materials into a wide diversity of products (such as food, dietary supplements, herbal medicines and cosmetics) that have multi-beneficial effects to human beings (Chang & Buswell, 2003b). In addition, mushroom cultivation can positively generate equitable economic growth. (b) Mushrooms are relatively fast-growing organisms. Some tropical mushrooms can be harvested and consumed within 10 days after spawning. By the use of appropriate strains, mushrooms can be cultivated all year round. They can be cultivated using traditional farming techniques in rural areas, or by using highly industrialized technologies in urban and peri-urban communities. (c) Mushroom cultivation can be labor intensive. Thus, the activity can generate new jobs, especially in tropical, less-developed countries. (d) While land availability is usually a limiting factor for many types of primary production, mushroom cultivation requires relatively little land space. Actually, they can be stacked using shelf-like culture systems. (e) Mushrooms have been accepted as human food from time immemorial and can immediately supply additional protein to human food. Other sophisticated and unconventional sources of food protein, such as yeast, uni-algal cultures, and single-cell proteins, have relatively more complicated requirements and need to be processed before they can be consumed. (f) Edible mushrooms should be treated as healthy vegetables. After improving the cultivation techniques, they should be cultivated as widely and as cheaply as other common vegetables, which will thus be beneficial to the general public. (g) In view of the pleasing flavor, high protein level, and tonic and medicinal values, mushrooms clearly represent one of the world’s greatest untapped resources of nutritious and palatable food for our current generation and for future generations to come.

Medicinal mushrooms have an established history of use in traditional oriental therapies. Many species of mushrooms have been used in traditional medicine for thousands of years. The use of mushrooms in traditional medicine has been documented throughout Asia, Europe, Africa, and Mesoamerica; however, many mushroom species are rarely eaten as food because they are woody and have a bitter taste.

Medicinal mushrooms have valuable health benefits. Mushrooms contain several biologically active substances (in fruit bodies, cultured mycelium, cultured broth, and spores) including high-molecular-weight polysaccharides (mainly β‎-D-glucans), heteroglucans, chitinous substances, peptidoglucans, proteoglucans (β‎-D-glucans linked to proteins), lectins, RNA components, dietary fiber; and secondary metabolite organic substances, such as lactones, terpenoids, steroids, statins, phenols, alkaloids, antibiotics, and metal chelating agents.

A total of more than 130 medicinal functions are thought to be produced by medicinal mushrooms and fungi including antitumor, immunomodulating, antioxidant, radical scavenging, cardiovascular, anti-hypercholesterolemia, antiviral, antibacterial, anti-parasitic, antifungal, detoxification, hepato-protective, anti-diabetic, and many other effects.

The best known medicinal mushrooms are: Ganoderma lucidum (lingzhi or reishi), Lentinula edodes (shiitake), Grifola frondosa (maitake), Cordyceps species (caterpillar mushrooms), Trametes versicolor (turkey tail), Flammulina velutipes (winter mushroom or enokitake), Agaricus brasiliensis (royal sun mushroom), Pleurotus species (oyster mushrooms), Hericium erinaceus (lion’s mane), Hypsizygus marmoreus (beech mushroom), Tremella mesenterica (yellow brain mushroom), T. fuciformis (silver ear mushroom), Phellinus linteus (black hoof mushroom), and Inonotus obliquus (chaga).

Mushrooms are rich in proteins, chitin (dietary fibers), vitamins, and minerals, low in total fat but with a high proportion of unsaturated fatty acids, and they have no cholesterols. As for the characteristics of taste, mushrooms serve as a delicious foodstuff and also as a source of food flavoring substances (because of their unique flavors). In addition to the volatile eight-carbon compounds, the typical mushroom flavor consists of water-soluble taste components such as soluble sugars, polyols, organic acids, free amino acids, and 5-nucleotides.

Regarding the beneficial nutritional effects of mushrooms, the following facts should be noted:

  • Mushrooms have a low energy level, which is beneficial for weight reduction.

  • Mushrooms have a not significant level of purine, which is beneficial for the diet of persons suffering from metabolic diseases.

  • Mushrooms have a low glucose level, and more mannitol, which is especially beneficial for diabetics.

  • Mushrooms have a very low sodium concentration, which is beneficial for the diet of persons suffering from high blood pressure.

  • Mushrooms have a high content of several key vitamins, which is an important orthomolecular aspect. This means that a significant part of the daily requirement of different essential vitamins can be covered by consuming mushrooms.

  • Mushrooms have a high content of potassium and phosphorus, which is an important orthomolecular aspect as well.

  • Finally, mushrooms have a high content of selenium, which is regarded as an excellent antioxidant.

Most mushroom-derived preparations and substances find use not as pharmaceuticals (“real” medicines) or botanical drugs, but rather as a novel class of products by a variety of names: dietary supplements, mycochemicals, tonics, functional foods, nutraceuticals, nutriceuticals, phytochemicals, biochemopreventives, and designer foods.

Several types of medicinal mushroom products are available on the market today.

  • Artificially cultivated fruit body powders, hot water or alcohol extracts of these fruit bodies, or the same extract concentrates and their mixtures.

  • Dried and pulverized preparations of the combined substrate, mycelium, and mushroom primordia after inoculation of semi-solid medium (usually grains).

  • Biomass or extracts from mycelia harvested from submerged liquid culture grown in a fermentation tank.

  • Naturally grown, dried, mushroom fruit bodies in the form of capsules or tablets.

  • Spores and their extracts.

Medicinal mushroom dietary supplements belong to a class of immunomodulators known as biological response modifiers (BRM), or adaptogens, or immunoceuticals, which are capable of stimulating immune functions. Regular intake of medicinal mushroom dietary supplements may enhance the immune response of the human body, thereby increasing resistance to disease and, in some cases, causing regression of the disease state. Medicinal mushroom dietary supplements enhance the cellular immune function and stimulate immunity in the body generally, to help maintain the correct balance between cellular and humoral immunity. Medicinal mushroom polysaccharides and other compounds prevent oncogenesis, show direct antitumor activity against various synergetic tumors, and prevent tumor metastasis. Their activity is especially beneficial when used in conjunction with chemotherapy.

A new class of antitumor medicinal mushroom dietary supplements and drugs has been called biological response modifiers (BRMs). The application of biological response modifiers or immunotherapy has become the new kind of cancer treatment together with surgery, chemotherapy, and radiotherapy. The best known anticancer drugs are, for example, Krestin, Lentinan, Sonifilan, and Befungin, prepared from different species of medicinal mushrooms. The best implementation of medicinal mushroom dietary supplements have been in preventing and maintaining immune disorder or a dysfunction of the immune system diseases, including autoimmune disorders, especially for immunodeficient and immunodepressed patients, patients under chemotherapy or radiotherapy, different types of cancers, chronic blood-borne viral infection of Hepatitis B, C, and D, different type of anemia, the human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), Herpes simplex virus (HSV), chronic fatigue syndrome, Epstein Bar virus, patients with chronic gastritis and gastric ulcers, caused by Helicobacter pylori, and patients with dementia (especially Alzheimer’s disease).

We should not assume that mushroom-derived products can be a substitute for modern medicine. However, we can recognize that generally mushroom-derived products are a special category that can serve a patient better under certain circumstances (e.g., enhance general wellbeing) and in some situations, serve to supplement other treatments (e.g., as a complement to modern medicine). As mentioned in the beginning, mushrooms are used as a health food, as dietary supplements, and as a medicine (drugs and botanical drugs) (Chang & Wasser, 2012; Wasser, 2010, 2014).The details of some of medicinal and dietary advantages, including relevant mushroom species have been reported by Chang and Buswell (2003b).

Concluding Remarks

Today we face many challenges for global human welfare involving inadequate regional food supplies, diminishing quality of health, and ongoing environmental deterioration. We urgently need to increase our knowledge and technology required for fair and effective global responses. Today, progress made in the fields of mushroom biology and biotechnology could provide tools to help reduce the burden of these issues or at least to aid in finding some reasonable solutions. Mushrooms can be used as food for a healthy state; pure refined products can be used in the diet, as medicine for compromised health, and crude extract products mainly can be used as dietary supplements (nutriceuticals) for a sub-healthy state, as well as for both healthy and ill states, as shown in the above Figure 2. Mushrooms are environmentally very friendly. They biosynthesize their own food from agricultural crop residues, which, just like solar energy, is readily available and sustainable. These crop residues would otherwise cause health hazards. Moreover, although physical and chemical technologies may, in some cases, play important associated roles, mushroom production can often be applied to situations where large-scale capital-intensive operations are inappropriate. The term mycoremediation refers specifically to the use of fungal/mushroom mycelia in bioremediation. The multi-dimensional nature of the global mushroom industry, its role in addressing critical food shortages facing human kind, and their production, which has a positive contribution to environmental pollutions, are to be measured. Furthermore, mushroom production and distribution can serve as agents for promoting equitable economic growth in society.

Nevertheless, challenges remain, and concerted efforts are required in many areas, including, for example, the domestication of new edible and medicinal species. Due to uncontrolled gathering and wild harvesting, highly prized edible mycorrhizal mushrooms are already rapidly diminishing, and research into devising methodologies for the artificial or semiartificial cultivation of wild mushrooms is now a priority. Further improvements in the production of existing cultivated species, including year-round cultivation of “seasonal” species and better quality control, also need to be addressed. Mushrooms are a unique group of fungi through which we can pilot a non-green revolution (white agricultural revolution) in less-developed countries and in the world at large. Mushrooms demonstrate great potential for generating great environmental and socio-economic impacts in human welfare on local, national, and global levels.

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