Mushrooms are the reproductive bodies formed by certain fungi. Just like the apple on a tree, mushrooms are the “fruits” of these fungi. The actual organism that produces the mushrooms is called MYCELIUM, a strand-like mass of white cells (also known as hyphae) found in the growing substrate which may be a dead tree stump, a live tree, or organic material in the soil.
Fungi reproduction depends on the existence of specific environmental conditions, especially the moisture or humidity level, the temperature, and the availability of nutrients including minerals and oxygen. Optimum conditions vary among species. Under the right conditions “fruiting” occurs and the mycelium produces mushrooms. When mature, the mushrooms release millions of spores into the environment for further propagation of the species.
Mushrooms are classified into three types according to their specific growing characteristics.
Parasitic mushrooms attack a living host plant, usually a tree, and eventually kill it. They may also be found growing on dead trees, but they probably started growing while the tree was alive and contributed to its demise. An example of a parasitic mushroom is the Honey mushroom (Armillaria mellea).This type of mushroom can be cultivated but will require a living host. Some parasitic mushrooms also function as saprophytes (described below).
Mycorrhizal mushrooms form a symbiotic (mutually beneficial) relationship with the roots of trees or bushes. In fact, the root tips of all plants are coated with a fungus which breaks down the organic matter in the soil and makes it available to the plant. The plant in turn produces sugars and exchanges these with the fungus. Some of these symbiotic fungi produce mushrooms. Examples include the Boletes, Truffles, Chanterelles, and Amanitas. Cultivation of this type of mushroom requires the other half of the symbiotic relationship which is the live tree. It is almost impossible to establish this symbiotic relationship under controlled conditions on a commercial basis. However, success has been achieved with truffles whereby a grower inoculated the roots of small oaks with the mycelium, planted them, and then waited for more than ten years before harvesting the truffles.
Saprophytic mushrooms live on dead organic matter such as dead trees, stumps, old roots, grass, straw, compost, etc. Mushrooms in this group are those that are successfully cultivated including Shiitake, Oyster, Champignons or White Button mushrooms (Agaricus spp.), Portobello, Enokitake, Reishi, Maitake, Paddy Straw mushroom, and many others.
All of these types of mushrooms play roles in ecosystems throughout the world. One of the key roles that mushrooms play in natural systems is the decomposition of dead organic matter. Decomposition is accomplished by a succession of saprophytic fungi (the following examples are edible species but I am sure there are many other). The primary decomposers such as Shiitake, Oyster, and Wine Cap mushroom (Stropharia rugoso-annulata), start the process by breaking down the lignin and cellulose in wood, straw and other plant matter. Secondary decomposers take over after the substrate has been partially broken down. Secondary decomposers typically grow on composted materials and include the White Button mushroom and Portobello (Agaricus spp). Tertiary decomposers are typically soil dwellers. Some soil dwellers can be cultivated in reduced/composted substrates and these include some Agaricus species (button mushrooms and Portobello), the Orange Peel mushroom, Conocybe, Agrocybe, and some Pleurotus species. On the other hand many of the soil dwelling mushrooms are extremely difficult to cultivate at all because they grow in nature only in association with the roots of trees and bushes and many also depend on soil organisms in order to thrive. These latter species include morels, truffles, and chanterelles. As mentioned above these mushrooms are classified as ‘mycorrhizal’ and are not only notoriously difficult to cultivate but can take many years to establish.
Each mushroom has specific growing parameters relating to light, moisture/humidity, temperature, availability of organic compounds and minerals as well as oxygen and/or carbon dioxide. In many cases the mushroom requires a ‘suite’ of environmental conditions which must be fulfilled for successful cultivation. These precise conditions can be quite difficult to reproduce. For example, the growth stimuli that morels require for reproduction are so complex that cultivating them indoors in controlled conditions is a hit or miss procedure at best. They can be cultivated outdoors by preparing a site suitable to their growth and introducing the morel mycelium in form of spawn (mycelial culture grown out on grain or sawdust). On the other hand, Oyster, Shiitake, Shaggy Manes, Reishi and others depend on a less complicated interplay of stimuli in order to reproduce and have a very high success rate if instructions for cultivation are followed carefully.
Primary and secondary decomposers are the most suitable for cultivation since the mycelium of these species is usually quite vigorous and with proper cultivation techniques there is a high rate of success. In addition, substrates are readily available. The by-products from agricultural processes and the lumber industry are suitable substrates for mushroom cultivation and include hardwood logs for outdoor Shiitake cultivation, sawdust for indoor cultivation of many species, as well as grain husks and straw for Oyster cultivation.