Introduction to Mushrooms and other fungi

Introduction to fungi and cultivated mushrooms

Fungi

Fungi are one of the five kingdoms of living organisms. The others are Prokaryota (e.g bacteria), Protoctista (e.g protozoa and algae), Plantae, and Animalia.
Fungi are not to be confused with plants as they lack chlorophyll and therefore cannot photosynthesize their food from carbon dioxide and water. Instead, they absorb their food through thin filaments, which are called hyphae, made up of many cells arranged end to end. A fungus consists of these colourless threads of hyphae which grow through the substrate and then, if conditions are right, produce a fruiting body. This is what we recognise as the mushroom or toadstool. This structure is the means of producing spores and therefore reproducing the species.

Electronmicrograph of hyphae
(of the mushroom Pleurotus) provided
by Dra Carmen Sánchez, Laboratory of
Biotechnology, Research Centre for
Biological Sciences, Universidad
Autónoma de Tlaxcala, México.

The lifecycle for the cultivated mushroom Agaricus bisporus is represented graphically here. The fruiting bodies are different for each species, and there are many diverse and colourful examples, not just the white mushrooms seen in supermarkets.

Lentinula (Shiang-gu or Shiitake)
©Prof. S. W. Chiu.

The biological definition of fungi is that they:

	are eukaryotic (an organism that have DNA contained in a nucleus);
	grow as hyphae;
	have rigid cell walls containing chitin (a strong material made of nitrogenous polysaccharides);
	obtain nutrients by secreting enzymes and absorbing digestion products from the substrate;
	produce spores for reproduction and dispersal.

Cultivated Mushrooms

Mushrooms are cultivated around the world, global annual production being in the region of 8 million metric tonnes. They are an ideal source of food as they contain high levels of protein, containing all the essential amino acids and have virtually no cholesterol. Agaricus bisporus or the common cultivated mushroom is the most extensively cultivated mushroom in the world accounting for about 30% of the total crop. It is grown on composted straw and animal manure indoors where the temperature, humidity and carbon dioxide levels are tightly controlled. It is mainly grown in Europe, America, China and Australasia. There has been a big increase in the interest in more 'exotic' mushrooms in the last twenty-five years, and now species such as Lentinula and Pleurotus can be found alongside Agaricus in most supermarkets.

Agaricus bisporus
©David Moore

Lentinula edodes
©Prof. S. W. Chiu.

Lentinula edodes, or the Shiang-gu (the Chinese name, or Shiitake (the Japanese name), is grown on logs outdoors in forests. Environmental manipulation of the crop is achieved by heavy watering, shading or positioning the logs in areas of different microclimate. The cropping period is 3 to 5 years. A more intensive cultivation technique has recently been developed involving growth on synthetic logs with mainly sawdust and other agricultural wastes in plastic bags. Lentinula global production in the mid 1990's was 840,000 tonnes compared with 2 million tonnes of Agaricus. 80% of production occurs in China, though it is also grown in Japan and South Korea.

Pleurotus species or oyster mushroom. This can be grown on a wide range of plant wastes enclosed in plastic bags. Oyster mushroom production is light dependent. Some growers operate a 12 hour light cycle using fluorescent lamps. Pleurotus are the second most important mushrooms in terms of production, representing about 25% of the world market share today. Production of these mushrooms has increased by over 60% in the last 25 years. China is the major producer, though they are grown worldwide.

Pleurotus
©Prof. S. W. Chiu.

Other Cultivated Fungi

Here are some other fungi which are cultivated

Ganoderma
Some species of fungi are cultivated for medicinal properties instead of for food. Ganoderma is cultivated mainly in China where it is called lingzhi. It has been described as being able to prevent a wide range of clinical conditions including chronic bronchitis, coronary heart disease and cancer.

Volvariella volvacea or Paddy Straw mushroom.
This is another fungus cultivated for food. It made up around 6% of total world production of cultivated mushrooms in 1991. As its name suggests it is grown mainly on rice straw, though other wastes do make suitable substrates. Unlike other exotic mushrooms it is sold at an immature stage. A low yield and poor storage qualities have restricts the production of this crop.

Wild Fungi

Here are some images of wild fungi reproduced with kind permission of the photographers; even more images of this sort can be found on the Links to images page.

Calocera cornea ©Michael Wood	Clitocybe inversa ©Michael Wood

Psilocybe cyanescens ©Michael Wood	Ganoderma oregonense ©Michael Wood

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