A mushroom is defined as “a macrofungus with a distinctive fruiting body which can be either epigeous or hypogeous. The macrofungi have fruiting bodies large enough to be seen with the naked eye and to be picked up by hand”. In a narrow sense, the word mushroom also refers only to the fruitbody. Mushrooms used to be classified into the Kingdom Plantae, but now they belong to the Kingdom Fungi due to unique fungal characteristics which draw a clear line from animals or plants. Unlike green plants, mushrooms are heterotrophs. Not having chlorophyll, they cannot generate nutrients by photosynthesis, but take nutrients from outer sources. Most mushroom species are under the Basidiomycota and Ascomycota, the two phyla under the Kingdom Fungi.
Mushrooms breed by spores (seeds for plants). Under the proper conditions, spores germinate into hyphae (collectively, mycelia). Mycelia are filamentous and generally unseen with the naked eye. Germinated hyphae form primary mycelia, and then secondary mycelia through plasmogamy (hyphal fusion). They accumulate nutrients from the substrate (soil for plants) and colonize substrate. When stimulated by temperature, humidity, etc., the mycelial colony forms pins under certain conditions and grow to fruitbodies (fruits for plants). Young fruitbodies are called pins (buds for plants). Pins differentiate into a cap and stem forming fruitbodies. Under the cap, spores are produced in the gills.
Fruitbodies release spores in order to produce the next generation. This life cycle of mushroom is divided into two phases: vegetative and reproductive growth. Vegetative growth indicates linear growth of fungal mycelia dissolving complex substrate components into simpler molecules and absorbing them as nutrients. When low temperature, high humidity, much oxygen, and sometimes light are offered, the mycelia cease vegetative growth and begin to produce fruitbodies, which we call ‘mushroom’. This is reproductive growth. Mushroom cultivation can be said the practice of obtaining fruitbodies by artificially repeating these two growing stages. Mushroom cultivation requires enough understanding on the optimal growing conditions of each mushroom species and how to make favorable environment for both vegetative and reproductive growth of mushrooms.
Three Factors of Mushroom Cultivation
What spawn is to mushroom is like seed is to crop. Unlike spore, spawn is already at its mycelial stage growing on its own substrate such as sorghum, barley or sawdust. The life cycle of mushroom starts from spores, but growers inoculate mycelial origin spawn rather than spore origin spawn because of possible variations and mutations. The quality of spawn is one of the most decisive factors for successful crop. Therefore, growers need to use qualified spawn for commercial production. Spawn should maintain the strain characteristics and is propagated by subcultures. New strains are developed with genetic methods such as variation and mating. The various types of mushroom spawn include grain, sawdust, plug and liquid.
Mushrooms can be classified as 3 categories by their tropic pattern; saprophytes, parasites or mycorrhizae. The most commonly grown mushrooms are saprophytes, decomposers in an ecosystem growing on organic matters like wood, leaves and straw in nature. Raw materials can be used as substrate for primary decomposers such as oyster mushroom and enokitake which have lignocellulosic enzymes. On the other hand, secondary decomposers like button mushroom or straw mushroom require substrate degraded by bacteria or other fungi. Mushroom requires carbon, nitrogen and inorganic compounds as its nutritional sources and the main nutrients are carbon sources such as cellulose, hemicellulose and lignin. Thus, most organic matters containing cellulose, hemicellulose or lignin can be used as mushroom substrate. Examples are cotton, cottonseed hull, corncob, sugarcane waste, sawdust, and so on. However, demanded amount of each nutritional sources differs according to mushroom species. For example, button mushroom (Agaricus bisporus) requires relatively high nitrogen source, so the optimal C/N ratio of button mushroom compost is 17. On the other hand, oyster mushroom and shiitake require less nitrogen and more carbon source. Mushroom mycelia secrete digestive enzymes into the substrate and absorb the dissolved nutrients. Cellulose, the main nutritional source of mushroom is one of the most abundant organic matters on earth, but its digestive enzyme, cellulase is owned by several microorganisms including fungi. Here comes the reason mushroom is considered an important food source. Mushroom is the only one by which cellulose is dissolved and absorbed and transformed into food for mankind. Mushroom is also influenced by acidity of substrate. The optimal pH value of substrate ranges from 6 to 8, varying with mushroom species.
The last important factor for mushroom growing is providing an appropriate environment both for vegetative and reproductive growth. Not being protected by a skin layer, fungi are easily affected by their growing conditions. So it can be said that the success or failure of mushroom cultivation depends on the control of growing conditions. Environmental factors affecting mushroom cultivation include temperature, humidity, light and ventilation. Optimal levels of them at vegetative stage differ from those at reproductive stage. Mushroom mycelia can survive between 5 and 40℃ depending on the species. Mushroom mycelia grow well with the temperature range between 20 and 30℃. Pins form at 10-20℃, lower than that of mycelial growth by 10℃. Over 80% of the fruitbody is water. Substrate moisture content should be 60-75% and log moisture content, 35-45%. During fruiting, different relative humidity levels, ranging from 80-95%, are needed at the early, mid and latter stage. Though mycelia can grow without light, some species require light for fruitbody formation. Being aerobic fungi, mushrooms need fresh air during growing, but ventilation is more required for reproductive stage. No matter how well the substrate is colonized, it is useless if it fails in fructification. Therefore creating the optimal conditions for transition from vegetative stage to reproductive stage is crucial to successful mushroom cultivation. In conclusion, among the three factors, the most important is environmental control. By maintaining optimal conditions at each growing stage and for each species, growers can produce the desired yield of quality
Mushrooms in History and Different Regions
Mushrooms have been part of our human diet since time immemorial. They were used as food even before man understood the use of other organisms. Undoubtedly, mushrooms were one of man’s earliest foods, and they were often considered an exotic and luxurious food
reserved for the rich. Today mushrooms are food for both the rich and the poor. They can be grown anywhere as long as the conditions for their growth and cultivation are provided. Available mushroom technologies range in complexity from very high to amazingly low.
Mushrooms have been variously considered as a hedge against famine or a possible cancer cure. They do certainly have enormous potential for feeding third world peoples. In the West, mushrooms are regarded as a luxury food. But in many developing countries of the world, mushrooms can mean cash for the poor and a new source of nutrition. Even landless peasants can grow mushrooms as a valuable crop as long as they have the proper technology, the proper substrates, and the planting material called spawn. In some villages of India, it has been reported that farmers are growing mushrooms right in their own homes or immediate surroundings. Villagers growing mushrooms can rapidly begin to bring in more cash than some local landowners.
In some poor countries of Asia, the tropical Chinese straw mushroom (Volvariella volvacea) is grown in very simple traditional ways. This mushroom likes the hot humid conditions of the tropics and can be cultivated on beds made up of agricultural wastes such as straw or banana leaves. Within 2 weeks, fruitbodies are ready to be harvested.
Oyster mushrooms (Pleurotus spp.) are even more suited throughout the third world areas that are rich in plant wastes such as sawdust, sugarcane bagasse and others. Moreover, composting–the difficult preliminary step for button and straw mushroom–is not required for oyster mushroom cultivation. The oyster mushroom growing houses can be constructed of mud as in some villages in India, or made of bamboo and dried leaves as in most of Asia. In cooler areas, oyster mushrooms may even be grown outdoors if they are shielded from excessive sun. Oyster mushrooms are easily dried to provide for a longer shelf life and export possibilities.
Benefits Derived from Mushrooms and Growing Mushrooms
Nutrition of the mushrooms
The popularity of mushrooms is still based not on the nutrients that they contain but mostly on their exotic taste and their culinary properties, whether eaten alone or in combination with other foods. It is not well known that mushrooms are full of nutrients and can therefore make a very important contribution to human nutrition.
Protein is one of the most important nutrients in food, being particularly important for building body tissues.
Mushrooms with protein content ranging from 3-7% when fresh to 25-40% when dry can play an important role in enriching human diets when meat sources are limited. The protein content is almost equal to that of corn, milk, and legumes, although still lower than meat, fish and eggs. As a dietary source of protein, mushrooms are superior to most fruits and vegetables with the exception of beans and peas. Mushrooms can be eaten fresh or cooked, unlike other protein sources such as soya and yeast that have to be processed or disguised in some manner before they are acceptable on the table. Mushrooms also contain all the essential amino acids as well as the commonly occurring non-essential amino acids and amides. Lysine, which is low in most cereals, is the most important amino acid in mushrooms.
Mushroom protein is indeed a valuable addition to the human diet. Mushrooms also rank quite high in their vitamin content, which includes significant amounts of Vitamin C. Although devoid of Vitamin A, mushrooms make up for that with their high riboflavin, thiamin and cyanocobalamin (Vit. B12) content, the latter usually being found only in animal products. Their content of the anti-pellagra vitamin–niacin–is nearly equivalent to the levels found in pork or beef, which are considered to be the richest sources of this vitamin. Mushrooms are also good sources of minerals such as calcium, potassium, sodium and phosphorous in addition to folic acid, an ingredient known for enriching the bloodstream and preventing deficiencies. Iron is also present in an appreciable amount in mushrooms and together with phosphorous, can provide a good proportion of the recommended daily dietary needs. Mushrooms are low in sodium, making them ideal for persons with certain types of heart and kidney ailments.
As health food and medicinal
For the past 20 years, interest in the medicinal aspects of mushrooms has greatly been stimulated by the large number of scientific studies conducted on mushrooms. Folklores have provided clues for potential sources of medicine from mushrooms as well as from herbal plants. Using modern approaches, scientists have isolated and identified specific components that can either destroy or at least debilitate three of mankinds’ killer diseases:
cancer, heart disease and AIDS. As a result, a vast body of scientific literature concerning mushrooms has been published since the 1970s, mostly in hospitals and research institutions in Europe, Japan, China and the United States.
The most recent introduction of a medicinal mushroom is Ganoderma spp. The fruiting bodies (Fig. 9) have traditionally been used for medicinal purposes and for thousand of years, have been regarded by the Chinese to be a high quality herbal medicine. It has been used clinically since ancient times in China for the treatment of fatigue, coughing, asthma, indigestion, neurosis and a variety of other diseases. Early reports indicated the ability of Ganoderma to improve body functions, increasing its healing ability while maintaining a healthy and long life. It is now well established from in vitro and in vivo studies that Ganoderma can help fight viral diseases, and modern research has proven its anti-tumor and interferon-inducing actions. Considerable data now indicates that Ganoderma basidiocarps have several components responsible for the inhibition of HIV multiplication. Today,Ganoderma is available in many countries in the form of dried fruiting bodies, capsules, tonic and instant teas (Fig.10), and is grown in culture all over Asia. In California, Ganoderma is sold in Chinese stores in dry forms, without the need for pre-processing into teas. Being a tropical fungus, this mushroom can be widely cultivated using sawdust and other tropical agricultural wastes such as palm fibers, coconut wastes and rice straw. Pleurotus spp., oyster mushrooms, are also good sources of beta-1,3/1,6-glucan. These molecules (called pleuran) stimulate the immune system of the body to help fight abnormal cells as well as boost the system against the damaging effects of chemo and radiation therapies used to kill tumor cells. Pleurotus also contains mevinolin and related compounds which inhibit reductase, an enzyme used in cholesterol biosynthesis. The consumption of oyster mushrooms can lower the cholesterol levels in the body. Vita-Glucan tablets and elixirs, formulated from purified glucan extracted from P. ostreatus, are now available for strengthening the immune system and lowering serum cholesterol levels to prevent heart disease. According to much folklore, Pleurotus can also prevent high blood pressure, impart long life and vigor and assist people in recovering from fatigue. It can also prevent hangovers, constipation and is an aphrodisiac. Other edible and cultivated mushrooms with reported scientific medical evidence are Lentinula edodes (shiitake), Agaricus blazei (himematsutake), Agaricus brunnescens (champignon) and Grifola frondosa (maitake). Those are known to induce the formation of interferon, a defense mechanism against some virus infections, and have displayed hypocholesteromic activity.
Use of agricultural wastes as substrates
Mushrooms are grown on some organic substrates, mostly waste materials from farms, plantations or factories. These otherwise useless by-products can therefore be recycled to produce value-added mushrooms. Currently,millions of tons of agricultural wastes are discarded, burned and neglected. In the process of mushroom growing,however, environmental pollution from such practices may be reduced. Examples of such agro-wastes in abundance in the tropics are straw, corncobs, grass, sawdust, sugarcane bagasse, cotton waste, oil palm waste, coffee pulp, water hyacinth plants, coconut husks, tree leaves, branches and logs. These all can be used alone or in combination to create mushroom growing substrate. With moderate effort and careful management, the very people hungry for food can have within their grasp a new food source in the form of cultivated mushrooms.
Income and job generation
Mushroom growing is labor-intensive, and for countries where jobs are scarce, mushroom growing can create jobs both in semi-urban and rural areas. In fact, some technologies can use family labor thus providing all members of the family with employment.
The labor of out-of-school youths and even school children
can also be utilized, especially as the bagging of substrate and related operations can be easily done by children. A big factory in Indonesia hires some 50 teen-age girls, who trim the mushrooms ready for canning and for export. Mushroom growing is also recommended as a project in a cooperative where division of labor is practiced. One group may be engaged in spawn production,
another group will do the substrate preparation, and still another group can take charge of growing condition management.
Resulting compost used for soil conditioner and animal feed
The used compost that remains after harvesting mushrooms may still be recycled for use as animal feeds and soil conditioner. Earlier studies of the author have demonstrated that spent compost of both Volvariella and Pleurotus had increased crude protein content compared with raw straw. Poultry feeding trials showed that spent compost fed to broilers resulted in greater weight gains compared with commercially used feeds. Low intake and low digestibility however were observed in trials with sheep using Volvariella-cropped rice straw/banana leaf compost. Research at the Hebrew University in Jerusalem included the production of a highly digestible nutritious feed for cattle and sheep from Pleurotus cotton waste/straw compost. Numerous studies have indicated that mushroom composts made from wheat straw and other supplements gave comparable or higher yields of such selected vegetables as cabbage, beans, celery and cauliflower when compared with those grown using poultry manure. In Puerto Rico, Pleurotus spent-compost made from sugarcane bagasse, has been used by local nursery growers as a good substitute for the expensive commercial fertilizers used in soil conditioning. The spent compost is further composted in the open air, covered with plastic for 4-8 more weeks before it is dried, bagged and distributed to nursery owners.
Case Studies Showing Economic Aspect of Mushroom Cultivation in Rural Areas
Case 1. Village contract growing of Pleurotus sawdust bags in the Philippines
The objective of this project was to pilot contract oyster mushroom growing and use the revenues for further expansion of mushroom growing in the rural area. This activity was successfully demonstrated in several small villages near the University of the Philippines which provided appropriate funding support to the participants and where a central laboratory prepared the seeded mushroom bags for fruiting. The support was mainly for the building of small (5 × 5m) mushroom houses made up of nipa and sawali (Fig. 19) or styrofoam. Each month, 2,000 bags (Fig. 20) were delivered to each of the participants (one from each village in the community). Resulting harvest was individually sold, to provide installment payments for the bags and the house. After 4 months when the project cost of PHP*20,000 (USD400) was recovered, the growers were taught to prepare their own bags, with the spawn provided by the central laboratory.
One of the problems encountered was the difficulty of providing the proper temperature (lower than 30℃) for mushrooms to fruit abundantly. This was not a problem during the cool season from December to February when growers would enjoy abundant harvests. There were also some initial problems of bag delivery which made cost and expenses relatively high. The problem in marketing was not due to lack of buyers of mushrooms but the lack of production. Supply does not meet the high demand from traders and restaurants.
Case 2. Bed production of the straw mushroom in the Philippines
This project was done in a small farming community in the province of Cebu where a foundation provided funds to the contract participants, mostly family-based groups. The spawn and supervision was provided by a laboratory, which was also funded by the foundation. Bedding materials consisted of 45cm long, 10cm wide bundled rice straw or dried and bundled banana leaves. Rice straw that was hard to bundle was chopped and
molded into a bed. Each 2m-bed would need at least 60 bundles and each family had to prepare 20-40 beds per month. The laboratory bought the harvested mushrooms back for marketing so the grower had no problem marketing their own produce.
Growers are expected to harvest at least 2.5kg of fresh mushrooms per growing cycle of 23 days. First flush would bring 2kg, and second flush, 0.5kg at the interval of 7-10 days. Each family therefore would produce at least 95kg of fresh buttons (Fig. 24, 25) and would have a net income of at least PHP2,000 (USD40) after removing the cost of spawn, production overhead/pesticides, monthly payback of loan and interest, as well as the monthly depreciation of their fixed investment in the form of water drum, sprayer and plastic sheets which have
an expected 3-year life span.