Mushrooms
Wild and Cultivated
MUSHROOM PRODUCTION
Of the three main groups of fungi - Saprophytes, Parasites and Mycorrhizal fungi - it is the Saprophytes that show the greatest potential for commercial production: as they grow on decomposing organic substrates (wood, humus, leaves, etc.), they can be cultivated in a controlled environment, if the right conditions are guaranteed for the growth and fruiting of the species of interest.
For each species, the growth factors in a natural environment must be replicated throughout the different stages of development in a controlled environment, with the following physical (temperature and lighting), chemical (substrate and humidity) and environmental (aeration) factors being of particular importance:
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Temperature: the temperature of the substrate and the surrounding environment should be variable depending on the stage of development of the culture, from substrate inoculation to fruiting. Most saprophyte species grow well at temperatures of around 25ºC, while fruiting is promoted by slightly lower temperatures (12ºC to 18ºC), mimicking late summer in a natural environment.
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Lighting: since they do not photosynthesize, light is not a requirement for the proper development of saprophytic fungi in the incubation phase (growth of the mycelium), and may only affect the shape, appearance, and color of the carpophores (mushrooms) in the fruiting phase. Generally, the incubation of the mycelium takes place in an unlit environment, with fruiting and mushroom production taking place in penumbra or half-light.
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Substrate: in terms of production, the substrate is defined as the material, or set of materials, used by the fungus as nutrition and support for its development. Each species prefers a particular substrate, or set of substrates, with the pH (acidity or alkalinity) and nutritional profile (amount of Carbon, Nitrogen, Phosphorus, Potassium, Calcium, etc.) being the most decisive factors for proper crop development.
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Humidity: both the humidity of the substrate and that of the surrounding environment is extremely important for the incubation and fruiting of saprophytic fungi cultures. Substrates that are too dry can affect the development of the mycelium and result in small, shriveled or deformed carpophores. Excessive humidity, on the other hand, can create conditions for bacterial infections or contamination by other fungi, which will make the production and marketing of the target species unviable. In general terms, substrates should have humidity levels of around 50%, while the surrounding environment should have higher levels, between 85% and 95%.
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Aeration: like all living things, fungi also need to breathe. Oxygen (O2) is necessary for the processes of digestion and assimilation of nutrients from the substrate, while carbon dioxide (CO2) is used for the multiplication and growth of the mycelium and reproductive structures. Ventilation of production sites is therefore extremely important and is sometimes difficult to balance with the temperature and humidity requirements of the different species.
Main Cultivation Methods
“Natural” methods
"Natural" cultivation methods are those that mimic the development of saprophytic fungi in nature, using unshredded woody substrate (i.e. wood stumps, trunks or logs), not subjected to a sterilization process or the addition of nutrients, and are essentially of two types:
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Stump cultivation: consists of inoculating cut tree stumps in situ with the mycelium of the species of interest. Development outdoors is naturally conditioned by climatic conditions and production is markedly seasonal;
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Log cultivation: like stump cultivation, log cultivation consists of inoculating freshly cut logs with the species of interest by drilling or cutting into the wood. The inoculated logs can be kept outdoors, subject to climate variability, or stacked in a relatively controlled environment (warehouses or production hangars);
In both systems, carpophore production can last for several years, until the substrate runs out of nutrients or is contaminated by other microorganisms.
Main cultivated species: Oyster mushroom (Pleurotus ostreatus), Shiitake mushroom (Lentinula edodes), Poplar mushroom (Agrocybe aegerita).
Industrial cultivation methods are based on the production using triturated substrates, which are more or less complex in terms of composition, granulometry and nutritional content: cereal straw, wood pellets, dried leaves and crop residues rich in lignin and cellulose are the most commonly used raw materials. These substrates can be supplemented with protein or vitamin additives, and always require a sterilization or pasteurization process in order to avoid competition and contamination by other fungi.
Industrial methods
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Cultivation in Trenches/ Mounds: a method that consists of depositing a ground substrate, previously sterilized or pasteurized and inoculated with the species of interest, in trenches or mounds, directly on the ground. These mounds are covered with a thin layer of soil which must be kept moist throughout the production cycle;
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Cultivation in Trays: a similar method to growing in trenches, with the variant that the substrate is placed in trays, which can be more easily handled and organized in racks and shelves. Unlike the trench method, tray production systems are generally developed in a protected environment (warehouses or production hangars);
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Cultivation in Bags: it is the most widely used method worldwide, as it guarantees the greatest control over the quality of the substrate and the characteristics of the mushrooms produced. It consists of filling plastic bags with inoculated ground substrate, making perforations on the sides to allow the mushrooms to emerge when they fruit;
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Growing in Jars: this is a simple variation on the previous method, but in glass or plastic jars with wide mouths so that the carpophores can exit vertically. It has the advantage that the jars can be cleaned, sterilized and reused after each production cycle;
The cultivation in trenches, trays and jars is the most suitable method for producing mushrooms with superficial/vertical fruiting: Portobello or Paris mushroom (Agaricus bisporus), Blewits (Lepista nuda) and Shiitake (Lentinulas edodes). Growing in bags is generally used to produce mushrooms with lateral growth: Oyster mushrooms (Pleurotus spp.), Shiitake mushrooms (Lentinula edodes) and Lion's Mane mushrooms (Hericium erinaceus).
References
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Machado, H. et al (2020) COGUMELOS EM PORTUGAL – Tradição e Novas Abordagens. INIAV
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Sanchéz Rodríguez, J.A. et al (2004) Los Hongos, Manual y Guía Didáctica de Micología. IRMA