The golden rule for testing edible mushrooms is never to experiment with fungi that you have not identified with certainty as harmless. It is only fair to point out that there are many fungi that are both edible and excellent, and in many countries they have formed part of the human diet for centuries (1,2). They are highly valued as a food source worldwide, and more than 30 species are sold commercially. Edible mushrooms contain more protein than any vegetable and are rich in vitamin B (3). The most delicious mushrooms include Boletus edulis, Clitopilus prunulus, Macrolepiota procera, Cantharellus cibarius, and Tricho-loma matsutake. All edible fungi should be picked when young and fresh and cooked as soon as possible. The commercially grown products are much safer because growers have been aware over the years of the problems that exist. Also, the strains marketed today are those with a long history of reliability as edible species (3,4).
The observation that certain edible mushrooms grow naturally on certain decomposing organic matter and the desire to produce a tasty source of food have led to the development of various techniques for the cultivation of mushrooms, and in some cases they have been fairly profitable. The cultivated species, however, have never been the most prized by gourmets. The favorite types are still the boletes, specific species of Amanita, and truffles; all of them are mycorrhizal fungi, and their carpophores cannot be developed without the right symbiotic plant (1). To date, the only successes have been with the saprophytic species, that is, those that feed on dead organic matter. Among these the best known is undoubtedly the champion, Agar-icus bisporus, which has given rise to a thriving agricultural industry. Each year millions of tons of these mushrooms are produced for direct consumption, for the canning industry, and for the preparation of soups and sauces.
In recent decades the microbiological industry has been enormously improved, and the production of mushrooms in a controlled environment has become an example of highly advanced technology. Today horse dung still constitutes the basis of the culture soil (5). With a given quantity of straw and droppings, the dung initially undergoes a process of natural though controlled fermentation, first out of doors and then in an enclosed area where it is enriched with nitrogenous sugar substances and vitamins required for the development of the field mushroom. After a variable period of time, depending on the composition of the substrate, now called compost, sowing takes place, using cereal seeds covered with Agaricus bisporus mold. Two main varieties of field mushrooms are used: white and brown. The white are better suited to canning, whereas the brown, with their hazel-colored cap and small brown scales, are more widely used in Europe for direct consumption because the flesh is firmer and tastier. The American preference for the white variety is an expression of the same prejudice reflected in the choice of white eggs, bread, and sugar (4).
The cultivation of the oyster mushroom, Pleurotus os-treatus, and closely related species is also highly devel oped, especially in the Orient. They are also found in western markets in various varieties. Volvariella volvacea (paddy straw mushroom) (6) and Lentinula edodes (shiitake mushroom) (5), common in Oriental cuisine, can now be obtained in speciality shops in North America. For other species, such as the morels, production techniques had been developed (5,7). Production lines are being launched for Stropharia rugosoannulata and Agrocybe aegerita.
All the saprophytic species, especially those growing on wood, can easily be cultivated, even though in many instances they do not command a large market because of their meager amount of flesh. However, they can be cultivated on a small scale or at home by infecting unhealthy plants or dead stumps with fragments of the cap. The species that lend themselves best to this practice are Flam-mulina velutipes and Pleurotus ostreatus.
The cultivation of mycorrhizal fungi, which need to live with a host plant in order to produce their fruiting bodies, is a demanding undertaking. This is known as indirect cultivation. The mycorrhizal symbiotic type that is cultivated quite extensively in France is the legendary French or Per-igord truffle, the high quality and price of which amply justify the cost of installing artificial truffle beds and the long years of waiting before the carpophores can be picked. In centers of modern truffle cultivation, production is followed extremely closely and nothing is left to chance. The acorns are sterilized on the outside in a chemical bath or dip and are then put in direct contact exclusively with truffle spores. The seedings, which develop in small bags filled with sterilized earth, will have the truffle as the only symbiotic organism with which to associate. Once planted out in soil with the right characteristics and due care, they will start to produce their first truffles after about 10 years.
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