From time immemorial edible fungi have been collected from the wild but few species have been brought into cultivation. This is due to the complex and specific microbial processes and associations involved in their growth and development, and to the technical problems in developing substrates on which they will grow and fruit. About ten species are cultivated on a significant scale world-wide. In order of importance these are Agaricus bisporus (including Agaricus bitorquis), Lentinus edodes (shiitake mushroom), Volvariella volvaceae (Chinese mushroom, straw mushroom), Flammulina velutipes (winter mushroom), Pleurotus subspecies (oyster mushroom), Pholiota nameko (nameko or viscid mushroom), Auricularia subspecies (Jew’s ear) and Tremella fuciformis (snow mushroom). All the cultivated species are Basidomycetes with Auricularia and Tremella belonging to the Tremellales and the others to the Agaricales.

Cultivation of the different species is not distributed uniformly across the world. Production in a particular region is influenced by ethnic tastes and preferences, the natural environment and the availability of suitable substrates. In the west, cultivation is dominated by Agaricus with a very small but increasing interest in other species. By way of contrast, Lentinus is the most important species in the Far East, with a significant interest in a range of other species. Agaricus accounts for two-thirds of the world production of cultivated fungi and is the only species of significance cultivated in the British Isles. Mushroom cultivation is unique in that it provides the only profitable process for converting waste lignocellulose from agriculture and forestry into a useful, edible product.

It is very difficult for private gardeners to prepare composts on which mushrooms can be grown with a reasonable expectation of success. There are, however, a number of mushroom-growing kits available. These consist of prepared compost which has already been spawned and a bag of casing material. The packaging may be a plastic bag, a water-resistant cardboard or rigid plastic box, or a rigid plastic tub. This packaging doubles as a growing container and the purchaser simply follows the instructions enclosed.

Agaricus bisporus is cultivated on substrates prepared from cereal straw, that from wheat being preferred. Preparation involves two phases. In Phase one the straw or strawy horse manure is wetted, mixed with chicken manure and activators, and built into stacks. These activators provide a source of nitrogen and soluble carbohydrate which promotes the microbial breakdown of the straw in the stack. The commonly used activators are chicken manure and molassed malt waste. Fermentation develops and the stacks are turned at intervals of 2-4 days over a period of 7-14 days to maintain aeration and ensure uniformity. In Phase two the fermenting compost is transferred to a facility in which it is pastuerised at 55-60ºC over a period of 4-8 days in a process known as ‘peak heating’. At the end of this period the compost is cooled at 25ºC and inoculated with a pure culture of Agaricus mycelium (spawn) grown on cereal grain. The spawned compost is maintained at 25ºC for 10-14 days during which it is colonised by the fungal mycelium (spawn-running). The upper surface of the colonised compost is then covered with a layer of peat/chalk (casing) and the temperature lowered to 16-18ºC. The mycelium continues to colonise the compost and also invades the casing layer. After 18-21 days fruit bodies are initiated (pinning) and develop into the typical gilled caps. The crop is produced in flushes at intervals of 7-10 days over a period of 30-35 days. Production is then terminated by heating to at least 60ºC with live steam (cooking out), the spent compost removed and the facility cleaned in preparation for the start of the next cycle. The production cycle takes 12-14 weeks.

The microbiology of the substrates used for Agaricus has been intensively researched and is better understood than those for other cultivated fungi. Cultivation requires accurate control of the environment and particularly of temperature, carbon dioxide level, ventilation rate and evaporative capacity of the air at different stages in the production cycle. 25ºC is optimum for mycelial development but a lower temperature of 16-20ºC is required for sporophore initiation and development. High carbon dioxide levels are necessary to promote mycelial growth but they must be lowered for sporophore initiation and the correct development of the cap and stipe.

The crop may be cultivated in purpose-built sheds, in insulated ‘tunnels’ covered with plastic film, or in caves. The substrate may be contained and the crop produced in ridged beds on the floor, in tiered wooden trays, on metal shelves, in deep troughs or in open-topped plastic bags. The several processes in the preparartion and handling of compost, filling trays and shelves, spawning, casing, watering and clearance of the used compost are all highly mechanised.

Agaricus is subject to attack by a range of pests and diseases. The common pests are eelworms and the larvae of sciarid, cecid and phorid flies. The important diseases are fungal viruses, the bacterial pathogen Pseudomonas tolassi and the fungal pathogens Verticillium and Mycogone. Pests and diseases are controlled initially by the pasteurising process in Phase two, by strict attention to hygiene and by the manipulation and accurate control of the growing environment supplemented as necessary by appropriate insecticidal, fungicidal and biological controls.

Lentinus edodes or shiitake is the second most important cultivated fungus though it only accounts for 16% of total production. It is most important in Japan, where it is used both fresh and dried, and is also grown in the US, where over 40 strains are available. In nature the fungus attacks the wood of broad-leaved trees, mainly oak. For cultivation, trees are felled in the autumn and limbs 5-15cm diameter cut into 1m lengths. These are stored for 30-60 days and then inoculated with Lentinus mycelium cultured on sawdust or on small wooden wedges. 15-20 inoculations are made in each log after which they are first placed in a ‘laying ground’ for a year and then at the onset of winter in a ‘raising ground’. The latter is usually a shaded glade with a constant high humidity and a temperature range of 12-20ºC. Fruit bodies start to appear the following spring. There are two flushes each year, in spring and autumn, and production is maintained over a period of 3-6 years.

More recently the fungus has been grown on mixtures of sawdust, soya been meal and rice bran. Although yields are less than in the traditional method the production cycle is reduced to 6-8 months. Greater control is possible and the system lends itself to greater mechanisation.

Volvariella volvaceae is regarded as an expensive delicacy in China and other Asian countries; it is also grown in Nigeria and Madagascar. The substrates used are either fermented rice straw or composted cotton waste. Traditionally the crop was grown in the open but it is now most commonly grown in film plastic structures using cotton waste as substrate. The waste is first composted and then filled into tiered beds each about 10cm deep. These are inoculated with pure culture spawn and the temperature maintained at 35ºC. The substrate in colonised in about five days. No casing is needed but sporophore initiation is light-dependent. Fruiting bodies appear in about five days and develop to harvest in four days. The first flush lasts 3-4 days and a second can be sometimes be obtained about a week later. The product is highly perishable and has to be marketed quickly. The production cycle takes 5-6 weeks.

Flammulina velutipes is of about the same economic importance as Volvariella. In nature it is a wood-destroying species attacking broad-leaved trees such as aspen, willow and elm. The species is widely distributed through Europe, the Far East, Africa, North America and Australia. It was gathered wild in Japan for centuries but it is now cultivated on sterilised mixtures of sawdust and rice bran. The substrate is filled into 11/1.75 UK pt polypropylene jars, sterilised and then inoculated with pure culture spawn. Colonisation takes 20-25 days at 22-25ºC. Fruiting is controlled by adjusting the temperature and humidity first to 10-12ºC and 80-85% relative humidity until the first fruit bodies appear. The temperature is then dropped to 3-5ºC until the fruit bodies are 2cm long, when the temperature is raised to 5-8ºC and the relative humidity lowered to 75-80%. The developing fruit bodies in the neck of the jar are supported by a cylinder of waxed paper. At harvest the wax paper is removed, the clump cut and marketed whole. The production cycle takes 12-20 weeks.

Pleurotus ostreatus, the oyster mushroom, is a wood-degrading saprophyte widely distributed through the temperate regions. It is popular in Japan and Central Europe. The substrate is prepared from chopped straw supplemented by corn cobs and soya bean flour. The mixture is packed into trays or boxes and pasteurised at 70-80ºC for 24 hours. After cooling the substrate is packed into boxes or plastic bags, inoculated with grain spawn and kept at 25-30ºC in a dark room.

Colonisation takes 2-3 weeks, after which the blocks of substrate are removed from their containers and stacked in tiers so as to expose the maximum vertical surface for fruit body development. Fruit body initiation is light-dependent and the crop is lit with fluorescent tubes on a 12-hour cycle. During cropping the temperature is maintained at 10-12ºC. The Production cycle takes about 70 days.

Pholiota nameko, together with Lentinus, Flammulina and Pleurotus, is among the four most important fungi cultivated in Japan. The species was originally grown on hardwood logs of Fagus (beech) or Quercus (oak) partly embedded in the soil. This has given place to culture on sterilised mixtures of sawdust and rice bran, a technique developed in Japan and Taiwan. Two strains of the fungus are used, a high-temperature strain growing at 15ºC and above which fruits in mid-summer and a low-temperature strain growing below 15ºC and cropping in late-summer to early autumn.

Auricularia is popular in China, where it is cultivated on logs of broadwood trees in a similar manner to Lentinus, the logs cropping for a period of 3-6 years. In Taiwan cultivation has been developed on a sawdust/rice bran substrate. This is compressed into plastic bags to form a cylindrical cake. These cakes are sterilised, cooled, inoculated with mycelium and maintained at 28ºC or less. When the blocks are colonised they are removed from the bags and stacked in frames to give a vertical wall of substrate on which the fruit bodies develop. The harvesting period is shorter than on logs but 3-4 flushes are obtained in each cropping cycle. The crop is dried and not sold fresh.

Tremella fuciformis is popular in China, Japan and Taiwan. Cultivation is on logs, using a technique similar to that for Lentinus and Auricularia. Gelatinous fruit bodies appear about eight weeks after inoculation and cropping continues for about seven months of each year for a period of 3-6 years. The mushrooms are washed after picking. Some are sold fresh but most are dried; they are usually stewed with fruit.

Tuber, the highly prized truffles belonging to the Ascomycetes, develop from a mycorrhizal association between the fungus and the appropriate trees, oaks, beech and hazel in particular. They are not cultivated in the same sense as the fungi described above, but methods have been developed in which tree seedlings have been are inoculated in a nursery to establish the mycorrhizal association, following which the ‘truffled seedlings’ are planted in suitable areas, such as old vineyards, for which a number of criteria have to be met. Truffles of different kinds can be grown in parts of France, Italy and Spain, and presumably in Portugal, Bulgaria and Yugoslavia where they also exist naturally. Harvesting is still carried out with pigs or dogs since digging up tree plots disturbs the mycorrhizal association and may destroy productivity, so that yields depend on the skill of the harvester as well as the weather and the age and management of the plot.

The stalks and caps of mushrooms may be tunnelled by the maggots of various flies including those of fungus gnats (Sciaridae), gall midges (Cecidomyidae), often referred to as cecids and phorid flies (Phoridae). The larvae of fungus gnats have conspicuous black heads and are up to 5mm long; those of phorids are a little shorter and thicker with the head end tapering and a blunt hind end; the larvae of cecids are much smaller, with two spots behind the head and the body tapering at both ends. Mushrooms may also be attacked by various mites including tarsonemid mites namely the mushroom mite (Tarsonemus myceliophagus); red pepper mites (Pygmephorus subspecies) with minute yellow-brown to red-brown mites that can swarm in vast numbers over the beds; and tyroglyphid mites, with soft translucent white bodies clothed with long hairs, that cause pits to develop on the stalks and caps. Other pests injurious to mushrooms include the mushroom eelworms (Aphelenchoides composticola and Ditylenchus myceliophagus), woodlice, millipedes and slugs.