Biotechnology for edible mushroom culture: a tool for sustainable development in Mexico
G. Mata , R. Gaitán Hernández & D. Salmones Red de Manejo Biotecnológico de Recursos, Instituto de Ecología, A.C, Mexico.
Abstract
This is a general study of fungi cultivation in Mexico, presenting relevant data about the use of some species as food. Despite Mexico’s persistent fungus-eating tradition, until recently there was little research about edible fungi cultivation. Currently, commercial fungi production surpasses 40,000 tons, of which more than 95% are white mushrooms (Agaricus bosporus) and 5% approximately are mushrooms of the genus Pleurotus. Some other species are also grown, such as shiitake (Lentinula edodes). The technology used to grow edible and medicinal fungi uses recycled lignocellulosic biomass, such as agricultural and forestry wastes that would otherwise cause environmental pollution issues. Recycling such materials to obtain high-quality food for human consumption, with additional health benefi ts, helps sustainable development signifi cantly.Keywords: Mycophagism, shiitake, lignocellulosic fungis, Agaricus bisporus, Pleurotus spp.
1 Introduction
Since ancient times, fungi has been linked to mankind through the production of traditional foods and drinks, and also by the use of some basidiomycetes associ-ated with ceremonial or medicinal rites. Indicia of fungus consumption has been found in the remains of several prehistoric cultures. There are records that from the time of ancient Greek civilization there were events associated with the use of fungi. Euripides describes in his works the intoxication of several members of a family caused by fungi. Some fungi were common foods during the Roman Empire; it is believed that the task to pick them up belonged to slaves. It is well
484 Ecological Dimensions for Sustainable Socio Economic Development
known that the edible fungus Amanita caesarea owes its name to the fact that it was a favorite food of Roman Caesars. Emperor Claudius was famously doomed by his taste for edible fungi, as his wife Agrippina mixed bits of a deadly fungus species (Amanita phalloides) in his customary mushroom meal [1].
Mexican people are ‘mycophagists’ (fungi eaters), with a long fungi eating tra-dition that goes back to pre-Hispanic times, and that is still very much alive today. The diversity of colors, shapes, and textures of fungi is remarkable at local markets during the rainy season, when fungi provide both a delicacy for the palate and a pleasure for the eye [2] (Fig. 1). In Mexico, more than 200 edible fungi species have been recorded to date [3], most of which have names that allude to their respective morphologic characteristics. Thus, some are called ‘clavitos’ (little nails), ‘elotitos’ (little corncobs), ‘panalitos’ (little honeycombs), ‘panzas’ (bel-lies), ‘escobetas’ (brushes), ‘trompas’ (trunks), ‘enchilados’ (spiced), or ‘azulitos’ (little blue ones); actually, many of the popular commercial species have main-tained their original native names, like ‘tecomates’, ‘tzensos’, ‘huitlacoche’, ‘totolcoxcatl and so on (Fig. 2).
The aim of this chapter is to focus on a small group of saprobes, which are greatly appreciated both for their organoleptic qualities and for their easy growth using farm compost. These mushrooms, also called lignocellulosic fungi, possess a complex enzyme production system, which allows them to degrade lignin and cellulose, turning these polysaccharides into low molecular weight sugars, like glucose, which are easily assimilated by them [4, 5]. The huge industry of edible fungi cultivation has been based on the exploitation of a few species within this group [6].
Figure 1: Wild edible mushrooms, ‘tecomates’ (Amanita caesarea), in a tradi-tional market in Mexico.
Fungi are considered the second more diverse life form group after arthropods; it is calculated that there are more than 2000 species, belonging to 30 fungi genera, labeled as edible in a worldwide scale. Nevertheless, it is estimated that only 80 species are grown experimentally, between 20 and 40 are grown commercially, and no more than 5–10 species are industrially produced. It is believed that the fi rst empirically cultivated fungus was Auricularia auricula (600 AD), followed by Flammulina velutipes (800 AD), and Lentinula edodes (1000 AD), all being culti-vated in the Asian continent [7]. White mushrooms, Agaricus bisporus, were fi rst grown in 1670 by La Quintynie, a gardener for the French king, at the Versailles Palace gardens. The cultivation of this species was quickly spread throughout the French capital, using old quarry mines as growth chambers [8]. Today it is estimated that the world production of edible fungi is around 27,000,000 tons. The most culti-vated fungi are white mushrooms (Agaricus bisporus), which represent nearly 32% of the total world production, while L. edodes, known as shiitake, contributes to 25% and Pleurotus spp, known simply as ‘mushrooms’, adds up to 14% [9].
3 Main edible fungi cultivated in Mexico
Although eating mushrooms in Mexico is a traditional custom, edible fungi growth is a fairly recent activity, going back no more than around 1930. Mexico occu-pies the fi rst place in Latin American production of edible fungi, providing nearly 60% of the continent’s production [10]. Following worldwide trade trends, the main cultivated species in our country are: Agaricus bisporus (white mushrooms, 94.3%), Pleurotus spp. (oyster mushrooms, 5.6%), and L. edodes (shiitake, 0.1%), with a 70% of the commercialized products being fresh [11]. It is estimated that edible fungi growth in Mexico is more than 46,000 tons per year nowadays [12].
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According to data presented by Martínez-Carrera et al. [10], the annual economic revenue for this activity amounts to nearly 200 million dollars and directly or indi-rectly generates around 25,000 jobs. Fungi production is mainly concentrated in the central part of the country, in specifi c regions of the following states: Estado de Mexico, Distrito Federal, Guanajuato, Hidalgo, Jalisco, Michoacan, Puebla, San Luis Potosi, Queretaro, Tlaxcala, Veracruz and, to a lesser extent, Chiapas.
White mushrooms are the most commercialized species worldwide, with a total estimated production of 3,000,000 tons per year [13]. The cultivation of this spe-cies was introduced in Mexico in the 1930s [14] and since then its production has been gradually increasing, returning 54% of the total volume generated in Latin America [15]. The production system used is the traditional method of two phases [13]. It was considered until recently that A. bisporus did not grow wild in Mexico, but new studies quote production data of strains of specimens collected in the fi eld [16, 17].
Mushrooms known in Mexico by the names ‘orejas blancas’ (white ears) or ‘orejas de patacan’ [18] were introduced to the Mexican market with the commer-cial name of ‘setas’ (mushrooms), because the initial cultivation technology came from Spain, where edible species are thus called. The fi rst attempts to cultivate Pleurotus go back to 1974, although research to adapt the growth technology to actual environmental conditions did not begin until 1983 [14]. The establishment of the fi rst test plant served as a learning center and reference for several national and foreign small producers [19]. Under those circumstances, a simple technology and accessible training favored the emergence of several small producers, which gradually had an impact on the regional and later national market. Furthermore, the diffusion of cultivation techniques, thanks to the publications of research cen-ters, was a valuable infl uence to share the accumulated know-how through the years of practical experience [6, 20–22]. Today, national production surpasses the rest of American countries, although it is relatively low compared to that of Italy, Spain, France, or China.
The Pleurotus genus is taxonomically complex, which is the reason behind dif-ferent studies aimed at determining the involved species in this important group of fungi [23]. Pleurotus pulmonarius and Pleurotus ostreatus are the commercially appreciated species. Their cultivation is based on the germplasm introduced to the country. To date, only Pleurotus pulmonarius has been found to grow wild in Mexico Camacho [24]; hence, the concern to commercially introduce Pleurotus djamor, a neotropical species that presents shorter cultivation cycles than the cooler zone species. There has been remarkable progress so far in crossbreeding and selection of Pleurotus strains [25–31], with the goals of increasing productiv-ity, to develop its fructifi cations in available non-conventional substrates, and to optimize cultivation systems in general.
L. edodes (Berk.) Pegler, called ‘shiitake’ in Japan, ‘xiang-gu’ in China or ‘pyogo’ in Corea, originates in Eastern Asia, where it is grown empirically since around 1100 AD [32]. Today shiitake is the second-most grown species world-wide, only surpassed by white mushrooms. Its cultivation is carried out by two methods that require different infrastructures and methodologies. The traditional
method is based on the use of logs, mainly from oak trees (Quercus spp.) which are inoculated with fungus mycelium produced in seeds or sawdust [33]. The mod-ern method is based on a prepared substrate made of sawdust or other components, which are sterilized in an autoclave or pasteurized with steam [34]. In Mexico, shiitake has been cultivated experimentally in diverse wood-based substrates made from tree species of the genera Carpinus, Bursera, Alnus, and Eliocarpus [35–37], and also from coffee pulp and sugar cane bagasse [38–40]. Research on shiitake in Mexico has been oriented to the use of different substrates and strains selection [35–37, 39–44]. The use of cereal straw for shiitake growth has been widely accepted in different European and American countries [45–47], due to the fact that such substrate is easy to handle and can be obtained with almost no dif-fi culty. Nevertheless, this method’s implementation requires the use of a spawn that favors the quick growth of strains and promotes the defense of the shiitake mycelium against the likely presence of antagonist molds from the Trichoderma genus [46, 48].
4 Germplasm conservation
Mushroom strain collections are fundamental tools for the development of the industry of edible fungi cultivation in Mexico. These collections have the main function of preserving fungi strains without morphological, physiological, or genetic changes until they are required for use. Conservation of those strains allows access to the particular genetic lines of organisms of interest, be it for study or commercial use. In Mexico, there are next to 11 fungi strain collections, of both edible and medicinal interest, which preserve a total of more than 1000 specimens. One of the main national strain collections is supported by the Instituto de Ecologia, A.C. (Veracruz); it was founded in 1982 and preserves more than 400 strains up to date, belonging mainly to the Pleurotus, Agaricus, and Lentinula genera (Fig. 3). Other research and education institutions in Mexico with important edible fungi strain collections are the Colegio de Posgraduados (CEICADAR, Puebla), Colegio de la Frontera Sur (Chiapas), and the Chemistry Faculty at UNAM [49, 50]. The preserving methods for germplasm vary among the collections, from the continu-ous transfers on the culture media, to the conservation in sterile distilled water and other long-term methods like cryogenics [51, 52].
5 Spawn production
Within the fungi production process, the availability of spawn or high commercial quality is essential to achieve success in this activity. In Mexico, the main com-mercial growers of Agaricus and Pleurotus must have a spawn supply from their own labs or bought from international prestigious companies, in order to guarantee the quality and certainty of the cultivated strain, and also to fulfi ll the timely needs of their trade. On the contrary, for small growers, spawn acquisition is one of the critical points of the process, for they depend on particular suppliers or research
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centers labs, whose capacity and quality does not always meet the standards of this growing industry.
Due to the polarized structure of Mexican industry, there exist a small number of large farms for the Agaricus cultivation and a great number of small producers dedicated to the growth of Pleurotus; thus, white mushroom spawn has low demand, and other mushrooms spawn is highly demanded. That is the reason why different academic groups have been dedicated to spread the technology by means of teaching courses, or even editing books and brochures [6, 21, 22, 53].
Although the methodology for spawn elaboration is an established protocol, some national research institutions continue to experiment with different aspects of spawn production. For instance, at the Instituto de Ecologia, A. C., several seeds and organic supplements have been evaluated in the spawn preparation of Agaricus, Pleurotus, and Lentinula strains, in order to optimize the wild and commercial germplasm resistance to the presence of antagonist mold strains frequently mani-fest in these cultures, specially Trichoderma and Monilia. According to results, the spawn supplementation with materials such as coffee pulp favors a quick myce-lium development during the incubation period of Pleurotus or Lentinula, which has a favorable repercussion on the fungus’ defensive mechanism [48, 54].
Figure 3: Strain of Pleurotus djamor for liquid nitrogen preservation.
In Mexico, white mushrooms are commercially produced applying the so-called American, Dutch, and French systems. The basic difference lies in the type and form of the container where the substrate (compost) is placed for fungi develop-ment. The American system is also known as ‘bed system’ and it is characterized by the use of a wooden base where the substrate is set. The Dutch system is a white mushroom production process using high technology; it is also known as the ‘tray system’. In the French system, the culture is made inside plastic bags, and it is widely used for its effi ciency and adaptability to different investment levels.
To cultivate white mushrooms, the substrate is put through the following pro-cess: 1) Open air fermentation (Phase I or compost) and 2) controlled fermentation (Phase II or pasteurization). Later, to complete the culture process, the compost is inoculated and the samples are incubated, production is induced and mushrooms are harvested. The fermentation consists of the transformation of the materials employed in the compost, to generate an appropriate substrate for the development of white mushrooms; this transformation occurs by the action of microorganisms such as bacteria and fungi. The materials used in Mexico depend on the production region – they can be straws from barley, wheat, oats, or sugar cane waste, among others. After the compost process, the substrate is subject to a thermal treatment called pasteurization in order to eliminate or reduce microbial populations that develop during fermentation, and thus obtain the ideal characteristics for white mushroom growth.
The inoculation is carried out at the end of Phase II, when substrate temperature is between 20°C and 24°C [9]. The process is performed with a prepared spawn in rye, oats, or millet seeds, among others. In Mexico, there are machines that auto-matically mix the substrate with the spawn, after which the product is placed in the containers that will allow fungi development.
Before fungi fructifi cation, it is necessary to apply a soil cover to the substrate. The soil cover is made with a combination of peat moss and other ingredients, and it has the function of keeping a microenvironment where humidity, tempera-ture, and CO2 conditions favor the appropriate development of fruiting bodies. Once the soil cover is invaded by mycelium, induction can begin. It consists of lowering room temperature from 27–28°C to 14–16°C, which causes primor-dia formation and, thus, harvest. In Mexico, areas of white mushroom produc-tion are, to a large extent, automated greenhouses that control environmental parameters (Fig. 4).
6.2 Pleurotus spp
For the cultivation of the Pleurotus genus species, a wide variety of lignocellulosic substrates have been used [6, 21, 55, 56] (Table 1). P. ostreatus (Jack.: Fr.) Kumm. and P. pulmonarius (P. fl orida Eger s. auct.) (P. ostreatus var. fl orida Eger) are the
490 Ecological Dimensions for Sustainable Socio Economic Development
leading species for commercial cultivation in Mexico and its production on differ-ent types of waste has had great development in other tropical countries.
Mexico produces a huge amount of organic waste, which represents an advan-tage for cultivating Pleurotus. Research on this mushroom in our country has encouraged the evaluation of several kinds of lignocellulosic waste, as observed in Table 1. A lot of research focuses on farm-waste optimization as culture substrate, and bioconversion of substrate to solid fermentation [20, 29, 57–59].
Figure 4: White button mushroom (Agaricus bisporus) cultivation. (A) House of commercial cultivation. (B) Mushroom production on compost.
For the Pleurotus cultivation process, the substrate fi rst undergoes a thermal treatment in order to reduce harmful microbial fl ora present in it. In some cases, substrates are fermented aerobically, mainly when there are great production vol-umes involved at an industrial level. This substrate thermal treatment is performed by two principal methods: pasteurization through hot water immersion or pasteuri-zation through steam injection. After this procedure, the substrate is inoculated with Pleurotus spawn under aseptic conditions. Under incubation conditions, the substrate is invaded by the mycelium, and later fructifi cations are developed under the control of environmental variables [6, 53] (Fig. 5).
6.3 Lentinula edodes
Shiitake is one of the best known and more studied fungi. This fungus has been usually cultivated in logs, but this production system has gradually been replaced by the plastic-bag cultivation system [9, 34, 55].
Table 1: Substrates used to grow some species of mushrooms in Mexico.
Pleurotus Lentinula edodes Agaricus Volvariella
Agave bagasse Sugar cane bagasse Peanut shell Sisal fi ber Coconut fi ber Corn husks Sugar cane leaves Viticulture residues Corn cob Wheat straw Barley straw Sorghum straw Rice straw Pangola grass Coffee pulp Pumpkin stubble Corn stover Tomato mulch Yam bean stubble Hibiscus stems Banana stems Oak chip Pine chip
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Traditionally, hardwoods logs were used for shiitake cultivation [86–88], but a faster and more effi cient system has focused on using a sawdust enriched substrate [89]. On the other hand, alternative (non-conventional) substrates have also been tried, although their availability and the adaptation of shiitake to them have been a limiting factor [90] (Table 1). The two main processes for shiitake cultivation are described as follows.
Log cultivation: log cultivation is seldom performed in Mexico; nevertheless, it has been traditionally used in Asian countries for many years [9]. The wood spe-cies employed for shiitake cultures belong mainly to the Fagaceae family, such as Betula, Carpinus, and Castanopsis, among others [9, 55, 91]. Logs are generally cut during autumn and can be inoculated 15–30 days later.
The appropriate log size is of 7–15 cm wide and 1–1.5 m long; 1–1.5 cm wide and 1.5–2 cm deep perforations are made on each log, with a 20–30 cm space between each from the log longitudinal axis and with 5–6 cm between each line from the axis. Two perforations are made for each 30 cm2 of wood. The spawn for the logs can be of mycelium in wooden pieces of the same size as the perforations, or of mycelium in enriched sawdust. Then, perforations are sealed, preferably with bee wax or paraffi n, to avoid spawn humidity loss and to prevent the entry of other microorganisms. The incubation period is 6–12 months depending on the tree spe-cies used, log sizes, spawn type, humidity, and temperature, among other factors. The best incubation temperature is 20–25°C. After this period, logs are submerged in water at 10°C for 12 h to induce fructifi cation. Afterwards, logs are placed in
Figure 5: Commercial production of oyster mushroom (Pleurotus pulmonarius) cultivated on barley straw.
natural or greenhouse conditions, arranged in a way that favors fungi production, with a temperature of 15–20°C and a relative humidity of 85–90%.
For the experimental production of L. edodes in Mexico, log cultivation has been replaced with the use of wood chips from different trees, such as Carpinus, Bursera, Alnus, and Eliocarpus, among others [35–37], and also some agroindustrial waste, such as coffee pulp, and sugar cane wastes [4, 38, 39]; even cereal straw and viti-culture residues [43, 60] (Fig. 6). Some of these materials were thermally treated by means of sterilization, but for most, the process has been substrate pasteurization at 65°C [46, 60].
Cultivation in bags or synthetic blocks: to cultivate fungi in bags, wood sawdust is used as the main ingredient, frequently combined with other complements in diverse formulations. Straw, corn cobs, and sugar cane bagasse are also employed. These materials are mainly supplemented with wheat bran, rice bran, millet, rye, and corn. Supplements serve as nutrient sources for optimal fungi growth [92, 93]. Ingredients are mixed and water is added until humidity reaches between 60% and 70%. The substrate is placed in heat resistant bags (2.5 kg per bag). Bags are usu-ally made of polypropylene and with a micropore fi lter to allow gas interchange. Bags are sterilized at 121°C for 1.5–2 h. The bags are cooled down and then inocu-lated using shiitake spawn. The mycelium covers the substrate in 20–25 days.
Figure 6: Commercial production of shiitake (Lentinula edodes) cultivated on wheat straw.
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After that the polypropylene bags are removed and the substrate is subject to a fructifi cation induction by low temperature or soaking. They can also simply be placed at the production area at 16–18 °C, and 85–90% relative humidity. Within 4–5 weeks primordia appear, and from 7 to 10 days fungi grow into adults. The main advantages of bag use instead of log production are that periods shorten and effi ciency increase. The culture cycle lasts from 4 to 6 months after inocula-tion, and until the last harvest. Biological effi ciencies vary from 75% to 125%. In contrast, the culture cycle in natural logs lasts around 6 years with a biological effi ciency of 33% [36, 89].
7 Factors affecting mushroom cultivation
Several factors affect mushroom cultivation, from production to postharvest. According to Fletcher et al. [94], the leading factors responsible for culture altera-tion can be classifi ed as: biotic (insects, nematodes, rodents, fungi, bacteria, and virus, among others); or abiotic (caused by temperature, environmental relative humidity, high CO2 concentrations and light, among others).
The insects that most frequently attack mushroom cultures are species from genera Lycoriella and Megaselia. These insects have wide geographic distribution and are common in Agaricus, Pleurotus, and Lentinus cultures. Although they can prosper at any stage of the process, these insects have a preference for the incubation phase, because they can oviposit on the substrate and their larvae feed on the mycelium. Larvae perforate the fructifi cations, and mushrooms do not have commercial acceptance in this condition. Furthermore, adult insects are carriers of other fungus diseases, in the form of spores or other pollutants attached to their legs. Female insects lay around 140 eggs and their life cycle is fully developed around 2–3 weeks. Other common insects are ladybugs, which are little beetles (Coleoptera) from genera Mycotretus and Pseudischyrus that feed mainly on fungi fructifi cations. To control this plague, protectors are placed on air entries of the commercial mushroom farm, and doors are kept closed.
Moreover, rodents like rats and mice cause the most damage in cultivation greenhouses of rustic construction. To control these, strict measures are followed in area access, and drains, sewers, and gaps are checked periodically.
Pathogen fungi constitute one of the main problems in mushroom farms, due to their frequency and resistance. These are mostly molds, whose appearance is due to factors such as inadequate substrate pasteurization processes, inadequate inocula-tion, or a lack of control of workers and facilities hygiene. Some of the most fre-quently contaminant fungi are Trichoderma – a widespread green mould, which can be found in several organic materials and the soil of various ecosystems; its wide distribution owes to its adaptability to different environments. This mold is very well known and harmful to the production of toxins and antibiotics. Its sexual state is Hypocrea, while it is less common in Pleurotus cultures, but more frequent in Lentinula, where it appears as patches of small, thick sprouts of white, yellow, or russet mycelium, soft when young and hard when fully grown. Different Trichoderma species may be found in fungi cultures; some are harmless and others
quite harmful, and so their antagonistic relationship to grown fungi is not yet fully understood, and varies from one species to the other [94]. The most associated spe-cies of this genus are Trichoderma viride, T. harzianum, T. aureoviride, T. koenigii, and T. pseudokoenigii. The spores of this fungus are quickly blown through the air, by insects, staff or by the equipment used in culture houses. Penicillium species are macroscopically similar to Trichoderma, as they are also green and dusty. Various Penicillium species are related to fungi cultivation, appearing in Petri plates, spawn, and substrates. Aspegillus can also be found polluting Petri plates, spawn, and sub-strate; it also grows on work tools and lab equipment. Its appearance is dusty and with several different colorations, from yellow (A. versicolor) to black (A. niger), but green strains, similar to Trichoderma and Penicilium, are also frequent.
On the other hand, abiotic factors affecting fungus fructifi cation include mostly ventilation, humidity, temperature, and light. The goal of controlling all of these factors is to create the right conditions during all phases of fungus culture. To some extent, all these factors interact in such a way so that, together, they are essential to the good development of fructifi cations.
Ventilation is required to move excessive carbon dioxide and perhaps other gases present in production areas. A lower ventilation results in the presence of long stipe, and a generally inadequate fungi development. With CO2 concentra-tions above 1000 ppm, increasing air fl ow is recommended, but ventilation param-eters should depend on the fungus species being grown.
Relative humidity is the relation between the amount of water in the air and the maximum amount of water that air may contain at any given temperature [55]. This is one of the most important factors in fungus growth and depends on the amount of water and ventilation in the production area. The recommended concen-tration is around 85%–95% [95].
Temperature affects the mycelium growth stage as well as the fructifi cation stage. The substrate produces heat, depending on the activity of microorganisms inside it. When the substrate reaches high temperatures (35°C), it can cause an increase of thermophilic microfl ora, which thrives at temperatures around 30–55°C [55]. When they start growing, these microorganisms generate more heat, which causes a temperature increase in the substrate and affects the mycelium’s adequate development. This excessive heat may be removed by introducing low-temperature air to the incubation areas. On the other hand, optimal fructifi cation temperature depends on the species or variety of fungus grown. Most grow at 18–20°C, but many others generate fruit bodies within the 10°C–25°C interval, although some species exceed these values [95].
Light is required for the normal development of fructifi cations by most grown species. However, there are some species, such as Agaricus and Volvariella, which need no light to fructify. The light requirement depends on each species, even on each strain within the same species. Poor lighting results on symptoms that are very similar to the ones caused by a high CO2 concentration, such as long stipe and small pileus. In the case of Pleurotus, the lack of light characteristically produces coral-like structures. As a general rule, an 8-h light cycle a day is enough for grown fungi.
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8 Cultivation of edible and medicinal fungi: a pillar for sustainable development
Despite the technological advances of the current human civilization, we still face complex challenges. The high population growth during the 20th century, and the great pressure human activities exert on natural areas and their biological pro-cesses, have drastically contributed to critically worsen the situation, endangering humanity’s sustainable development. The world’s annual population growth rate is 1.7%, so by 2050 world population is expected to have reached more than 9000 million people [9], most of which would live in underdeveloped countries. Pressure on natural resources will increase, and signifi cant advances will be required for the production and conservation of foods, environmental pollution control, and the betterment of public health systems. Even though the problem is complex and far-reaching, the biotechnology for edible and medicinal fungi cultivation, while not fully solving the issue, may provide some elements that help to mitigate it.
Doubtlessly, one of the biggest advantages of edible and medicinal fungi culti-vation is the possibility of using lignocellulosic waste from the agriculture and wood industries. It is thought that photosynthesis annually produces around 200,000 million tons of organic matter worldwide [96]. However, most of this material is not a directly edible resource, either by humans or animals, and in many cases it can become a source of environmental pollution. Most kinds of farm waste are substrates with a huge biotechnological value. Besides their uses to pro-duce edible and medicinal fungi, they can also be used to grow biomass-enriched animal food, to produce compost to be used as a fertilizer or pesticide, to produce enzymes, organic acids, ethanol, fl avoring additives, biologically active secondary metabolites, and also to bioremedy dangerous compounds and detoxify farm waste [97]. Also, research on medicinal fungi has demonstrated that several species pos-sess properties that help treatment of conditions related to viral, bacterial, para-sitic, cancerous, hypertension, atherosclerosis, hepatic, diabetic, infl ammatory, and oxidation conditions, and to help reduce cholesterol and regulate the immune system [97–99].
Mexico’s biodiversity offers interesting possibilities to incorporate certain spe-cies to fungal culture with certain well defi ned uses. Among medicinal fungi, the Ganoderma lucidum species stands out for its well-documented medical proper-ties. This fungus is massively produced in Asia, mostly in China, where it is known as Ling Zhi, and in Japan, where it is called [100]. G. lucidum cultivation could be introduced to Mexico’s relatively abundant subtropical areas, where the substrates for its culture are relatively easy to obtain. Some species closely related to G. lucidum are successfully growing in Mexico’s wilderness, and it would be relevant to study their qualities to produce metabolites and determine their medicinal properties.
Another interesting species that shall certainly become important in Mexico is Agaricus subrufescens (= A. blazei), an edible and medicinal fungus, considered a gourmet dish. This species was fi rst collected in Brazil, after which it has been intensively studied in Asia, where it was confi rmed that it can signifi cantly help to
activate the immune system [101]. Nowadays, A. subrufescens is commercialized under various names, which include 'cogumelo de vida', 'himematsutake','agarico de sol real', and 'hongo almendra'. The attractive of A. subrufescens culture includes mainly its ability to grow in relatively high temperatures, which would allow it to be widely grown in Mexico.
Perhaps the greatest opportunities for expansion of the fungi culture industry in Mexico can be found in tropical and subtropical species. There are many fungi species with domestication possibilities, particularly because subtropical species include many saprophyte strains. However, studies are generally scarce, which is why biological knowledge on species makes its domestication diffi cult. One of the most important tropical fungi is Volvariella volvacea (Bull.: Fr.), a species that is commercially cultivated mostly in Asia, and known as ‘paddy straw mushroom’ or ‘Chinese mushroom’ [102]. V. volvacea is not commercially grown in Mexico, despite many studies conducted since the 1980s [61–63] and the fact it is a very appreciated mushroom by the rural population, where it is known as coffee pulp fungus, chaff fungus, pink fungus and ‘pecho de gavilán’ [18]. V. volvacea’s growth characteristics make it an ideal species for production in tropical areas, since its incubation temperature lies between 30°C and 35°C and its fruiting can be obtained between 28°C and 30°C [102]. Although the V. volvacea species is well known for its fi ne taste, some studies have recently reported that this fungus also has immune-biological properties, which adds to the value of its culture [102].
Mexican biodiversity also offers the possibility to produce edible mycorrhizal fungi species. This subject should be approached in an integral fashion, including traditional knowledge of edible fungi in Mexico and the scientifi c and socioeco-nomic research conducted on the subject. Edible fungi are perhaps the most impor-tant forest resource besides wood. In some countries, particularly in Europe and Asia, there are forests maintained specifi cally to obtain mycorrhizal edible fungi, which fetch high prices in the local and international markets. Such is the case of truffl es, mostly Tuber melanosporum, matsutake (Tricholoma matsutake) and several species of the Boletus and Lactarius genera [8]. The application of technology for edible fungi could help obtain mycorrhizal seedlings through commercially important fun-gus species. Thus, governmental and research institutions in charge of protection of the environment, natural resources, and social development could offer arbor cultur-ists a broader species selection for reforestation, which would in turn allow for the commercialization of the edible fungi the seedlings were inoculated with.
Since mycorrhizal fungi are unavoidably associated with a host plant, the selec-tion of parental trees plays an essential part, as the mycorrhized seedlings should ensure the most biodiversity. This strategy could help the recuperation of highly deforested areas, offering the added value of producing food for human consumption.
9 Sustainability in edible fungi cultivation
The technological model for fungal culture can be transferred to groups repre-senting the industrial and farming environment, which has resulted in the great
498 Ecological Dimensions for Sustainable Socio Economic Development
number of small (and some large) producers nowadays. Most consider this culture system as simple and inexpensive, if done in a small scale. By the same token, this production process allows some farmers to adopt it as an additional activity, improving the local diet of the population by generating food with a highly nutri-tious and medical value. This encourages the participation of farmer women in the production process and the organization of its members. In addition, this activity generates jobs in the areas where it is practiced, bringing income and feeding [103]. As an example of this, we should mention the training and counseling the Instituto de Ecología gave to a group of producers at Las Vigas de Ramírez – a locality in Veracruz State, in Mexico – regarding the establishment and activation of a Mushroom Producing Unit (UPS, for its Spanish initials).
Las Vigas de Ramírez is located 40 km away from Xalapa, the capital city of the Mexican state of Veracruz, with an elevation of 2420 m. It comprises a surface of 108.57 km2, which represents 0.0014% of total state area. Its climate ranges from temperate to humid, with an average temperature of 20°C, and 1500 mm of aver-age annual precipitation. Its population is divided 50/50 between rural and urban areas. Its population’s main activities are farming – specifi cally apples, plums, corn, and wild fungi – cattle breeding and forest exploitation [104].
An UPS was established on the region, with the fi nancial help of federal and state governments. Said UPS has four tunnel greenhouses, as well as a concrete plant for substrate treatment, a room for steam pasteurization and inoculation.
The production process uses local organic substrates, such as chaff and bran, which are usually underutilized kinds of waste. Initially, the substrate is fermented prior to pasteurization. A substrate’s pasteurization temperature ranges from 60°C to 65°C, maintained for a 6–8 h period. The substrate is inoculated with commer-cial spawn, using transparent poly bags with a 15 kg capacity. Bags closed and labeled are put in greenhouses. Ambient temperature is kept at 20–25°C. The pro-ductive cycle spans 77 days, from running spawn period to last harvest. A green-house can store 1038 bags, each of which can yield 2.5–3 kilograms of fresh mushrooms. This adds up to the production of 12.4 tons of fungi per cycle. Allowing for a 15% loss, net production is 10.6 tons. Thus, average daily produc-tion amounts to 116 kg of mushrooms. Waste from fungi harvest is then used as compost to improve soil quality.
The culture of this fungus gives the population a job source and food for the entire year; in addition, they do not depend on local wild fungi collection for sale or consumption anymore, which will help stabilize the local wild mycobiota.
10 Conclusion
This chapter has tried to demonstrate the importance of edible fungus biotech-nology as a useful tool for sustainable development. Edible fungi culture is not only a time-honored farming practice, but also an activity that requires up-to-date technological and scientifi c knowledge. The entire process of edible and medici-nal species cultivation was developed based on disciplines such as microbiology, physiology, genetics, and industrial engineering. Using farming waste to produce
human food, as well as medicinal fungi and their bioactive substances, is a very important contribution to real sustainable development. Due to their health ben-efi ts, edible fungi will doubtlessly become one of the main components of human food in the near future.
Acknowledgments
The authors are grateful to the authorities of Instituto de Ecología A.C. for their support to carry out this paper. This work is part of research funded by the project ‘Identifi cación, aislamiento y cultivo de hongos micorrícicos del Cofre de Perote, Veracruz y pruebas de micorrización con plántulas de pino bajo condiciones con-troladas’ (Project 108654) fi nanced by FOMIX-CONACYT Veracruz.
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