Seeding Substrate and Management of the Vegetative Stage of Growing the Commercial Mushroom, Agaricus bisporus
David M. Beyer & Vija L. Wilkinson,
Department of Plant Pathology, Penn State University
The purpose of this fact sheet is to provide basic information on the process of seeding substrate and the management of the vegetative stage of growing the commercial mushroom, Agaricus bisporus. The process before this stage, substrate preparation and the processes after, casing and production, are discussed in other publications.
A mushroom is the fruiting structure of the fungus and consists of a cap and stem. The mycelium is the fine "root" system that grows in the composted substrate adsorbing nutrients and water. After fruiting is initiated and the mushroom matures, the cap opens and gills are exposed. These gills produce spores in huge quantities; for example, a three-inch mushroom produces 40 million spores per hour. In nature, spores germinate and grow very poorly; therefore, another method to seed the mushroom substrate is required. The mushroom mycelium (threadlike filaments that become interwoven) is propagated on a base of steam sterilized cereal grain (usually rye or millet). This cereal grain/mycelium mixture is called spawn. Most spawn is made with mycelium from a stored culture, rather than mycelium whose parent was a spore. This is because each spore is likely to yield a new strain and its performance would be unpredictable. Preparing spawn is highly technical task that is not practical for most mushroom growers to perform; therefore, it is mostly produced by specialized companies that supply growers with pure culture spawn. However, in some cases, it may be necessary for the growers to produce their own spawn. In such cases, access to cultures (cultivars) with proven productivity is a key component of a successful enterprise.