Author: András Geösel, PhD
Spawn making and using is an asexual method of propagation in mushroom growing. Spawn is some kind of a carrier colonized by the mycelia of the mushroom, which is added to the mushroom compost or substrate. Spawn is prepared by a number of commercial spawn manufactures.
Nowadays three types of carriers (material colonized by the mycelia) are available for mushroom production:
Millet spawn in commercial bag and under microscope
Plug spawn colonized by mycelia
Synthetic spawn under microscope
A short overview of the history of spawn making helps us better understand the reasons that lead to the making of these types of spawns, which are nowadays commonly used.
(by Francisco Arqueros)
1894: Constantin and Matruchot were able to achieve a controlled germination of spores from mushroom tissue and spores. This mycelium, known as 'pure culture', was then inoculated in sterilised horse manure. This substance was bottled and left to settle until the mycelium colonised the sterilised horse manure. Later, growers bought this substance, in theory free of disease. The final product (planting material) sold to growers as mushroom spawn.
1902: Ferguson, (in USA) published a description of the conditions in which a controlled germination of spores and the growth of mycelium could be achieved.
1903: Louis F. Lambert established the Lambert's pure culture spawn in Minnesota, since 1907 the Lambert's Company was marketing at least seven different pure strains of Agaricus bisporus.
1905: Ferguson and Dugger started pure mycelia culture from mushroom ’tissue’
1932: James W. Sinden patented grain spawn preparation protocol.
The current variety of white Agaricus bisporus, commonly found in supermarket shelves world-wide, comes from a single cluster of white mushrooms that was found in a bed of cream (brown) mushrooms in 1926. Until then all mushrooms had been brown. As with the mushrooms growing spontaneously in spent compost from melon beds in seventeenth century France, these white mushrooms appeared unexpectedly.
Nowadays the commercial spawn for companies are prepared by multinational companies. The laboratory background and breeding potential requires many investments, therefore the small entrepreneurs should have special cultivars or low-scale techniques for benefit production. The mushroom production business today use the traditional grain spawn for 80 years, recently new carrier are under development. The advantages of grain spawn (easy to mix into substrate, can store for long period, adequate for almost all mushroom species, etc.) must be present in any other spawn types for safe and short cropping circle.
The mycelia of most mushroom species are able to colonize different grains, that is why they are together suited for spawn making. Mainly grain based spawn is used in modern mushroom production.
Steps of spawn making are the following:
Strains are maintained, then inoculated to petri-dishes and at last the mycelia are transferred onto steam-sterilized grain.
The grain is usually rye (Secale cereale ) or millet (Panicum sp.), or sometimes wheat ( Triticum sp.), sorghum (Sorghum sp.) or bristle grass (Setaria sp.). Similarly to commercial seeds, the quality regulations for grains used for spawn are strict. The grain has to be clean, uniform, free of fungicides, soil, pests and weed seeds. Toxins produced by mould inhibits mycelial growth of cultivated mushrooms, thus the grain has to be completely mould free.
Spawn manufactures store the grain in special silos. The steps of grain processing are the following:
The stored grain is washed a few times to remove broken seeds, dust and soil. The washed grain is then soaked and cooked. During the 15-30 minute long boiling the grain is stirred. At the end, the seeds become soft, their inside lose their white colour and become transparent. The grain is left in the cooking water for 10-25 minutes to for water absorption to complete. If the grain is not cooked enough, they absorb less water, thus the colonization will be slower. If overcooked, the seeds stick together, which makes it hard to loosen them up and later to fill. The grain is then cooled, gypsum (CaSO 4) and limestone (CaCO3) is added (to loosen the seeds up) and the pH in adjusted to 7,4.
Perforated bags filled with grain ready for sterilization
In smaller spawn manufactures the next step is to fill the grain into heat-resistant bottles or bags (with special air vent perforations), which are then put into an autoclave. Sterilization is done in 2 hours, on 121 ˚C, in overpressure. The autoclaves of spawn manufactures are specially designed: they have two doors – one on the “contaminated” side, where the material is filled into the machine and one on the “sterile” side, where the sterilized material is taken out (and then mycelia is added). Intermediate spawn (made from mother spawn the same way commercial spawn is made) is added to the sterile material. The bags or bottles are opened, intermediate spawn is added than mixed and the bags or bottles are re-sealed.
The process of spawn making in smaller manufactures
In commercial/large scale spawn manufactures cooking, pH adjusting and sterilizing is done in the same steel tank. The sterilized and cooled grain is then mixed with the mother spawn itself, and then filled into bags under sterile circumstances. This method requires less manual handling and the risk of infestation is lower.
The process of spawn making in commercial manufactures
Colonization (spawn run) is similar in both cases. The bottles or bags are stored in clean rooms with filtered air. In case of button mushroom spawn production, the temperature has to be around 25˚C, otherwise span run will not be homogenous. Since mycelia needs oxygen and emits carbon dioxide, the bags cannot be completely sealed. In order to provide gas exchange, the bags are perforated, but to prevent infection, the perforations are covered by a special filter. As mycelial development produces heat, perforations are also necessary to prevent overheating. The bottles and bags are shaken on the 5-10 th day after inoculation, to help homogenous spawn run. At the same time, each bottle and bag is checked for any sign of infection. Spawn run is completed in 14-20 days in case of most mushroom species.
The stages of the 17 days spawn run
The colonized bags are stored on +2˚C. On this temperature, white button mushroom spawn can be stored for 8-10 months, while cream type’s for only a shorter period. To prevent overheating the spawn has to be kept on +2˚C during storing and transporting as well. If the spawn overheats, it becomes acid (the pH lowers), releases a liquid, becomes smelly and no longer can be used for spawning. That is why commercial spawn manufactures continuously monitor the entire process of spawn making from the point the grain enters until the ready spawn is sold and shipped, thus ensuring high quality.
Mushroom producers usually do not have to deal with the spawn directly, since it is added to the compost in the compost plants and arrive to the grower only as a component of phase II. or phase III. compost.
Some growers prepare spawn themselves in small scale, or buy spawn and add it to the compost or substrate. This case the grower has to be aware of the most important quality criteria of spawns, which are the following:
Since the procedures and techniques of mushroom breeding and hybridization exceed the purposes of this curriculum, only the basic, most important information are presented.
Preparation of monospore and multispore cultures are classical breeding methods. Monospore cultures can be started from spores of fruitbodies, by inoculation of primer hyphae, which is followed by anastomosis.
Multispore cultures are prepared by using spores of two fruitbodies. The spores are mixed in sterile water then spread on media. The near hyphae clamp by each other and the hetero-karyons are then inoculated and selected on media. The selected strains are tested in growing experiments.
By the development of molecular biology creates new ways in mushroom breeding. Besides the traditional methods, new techniques were introduced to the breeding of button mushroom first, then to other mushroom species as well. These methods (e.g. isozyme analysis; RFLP, AFLP and SCAR analysis) can be used for identification and characterization of the already existing strains. Other techniques (e.g. somatic hybridization, gene introduction) are used for creating new strains.
By 2010 the gene sequencing of Agaricus bisporus was finished (http://genome.jgi-psf.org/Agabi_varbisH97_2/Agabi_varbisH97_2.home.html ) and is now available for further gene-based breeding purposes. Although it would be possible to make GMO varieties, unlike in case of arable crops, GMO mushrooms are not likely appear in cultivation.
1. What is mushroom spawn?
2. What kind of spawns do we use?
3. What are the steps of spawn production?
4. What are the advantages of the synthetic spawn?
5. What are the quality criteria of spawns?
Chang, S.T., Miles, P.G. (2004): Mushroom Cultivation, Nutritional Value, Medicinái Effect, and Environmental Impact. CRC Press Boca Raton, London, New York, Washington.
Francisco Arqueros: Spawn the story so far. http://www.themushroompeople.com/showArticle.asp?id=1770
Győrfi, J. (szerk)(2012): Gombabiológia, gombatermesztés. Mezőgazda Kiadó, Budapest.
Lelley, J. (1997): Die Heilkraft der Pilze. Econ Verlag GmbH, Düsseldorf und München.
Oei, P. (2003): Mushroom Cultivation, Backhuys Publishers, Leiden, The Netherlands.
Sinden, J.W. (1936): Mushroom spawn; an improvement. United States Patent Office, Patented, Number: 2,044,861.
Stamets, P. (2000): Growing Gourmet and Medicinal Mushrooms. Ten Speed Press, Toronto, Kanada.
Stamets, P. (2005): Mycelium running. Ten Speed Press, New York, USA.
Szili, I. (2008): Gombatermesztők könyve. Mezőgazda Kiadó, Budapest.
http://website.nbm-mnb.ca/mycologywebpages/NaturalHistoryOfFungi/DikaryaDiscussion.html
http://www2.mcdaniel.edu/Biology/botf99/fungifromweb/basidomycetes.html
Az "Angol és magyar nyelvű, digitális tananyagok fejlesztése a BCE kertészettudományi kar kertészmérnök és multiple degree hallgatói számára" pályázat a TÁMOP-4.1.2.A/1-11/1-2011-0028 pályázati projektek támogatásával készült.