B y far the most crical step is that of primordia formation, called the initiation strategy. An r it ation strategy can be best described as a shift in environmental variables, triggering the formation of mushrooms. The four major environmental factors operative in an initiation strategy are: moisture, air exchange, temperature and light. These are adjusted accordingly:
Moisture: C"-ect watering is applied, coupled with a constant, controlled rate of evaporation to mahiain high humidity between 95-100%. Fog-like conditions are
important when aonal mycelium is first exposed to the growing room environment. Once primordia form, a gradual reduction of humidity from 100% to 90-95% usually is beneficial. Humidity should be measured in at least three locations in the free air spaces directly above the mycelium-pen neated substrate
Air Exchange: Air is exchanged to precipitously lower carbon dioxide and io suddenly provide oxygen. CO, levels should be belc / 1000 ppm, ideally below 500 ppm for maximum mushroom formation. Air exchange should be adjusted specifically to lower CQ, to the specified levels outlined for each species in 'he following growth parameters.
Temperature: Many strains will not form mushrooms unless temperate is dropped or raised to a critical plateau For most strains, a temperature drop is required. Since mush room formation is primarily a surface phenomena the atmosphere of the growing room has to be altered to affect a temperature change in the substrate. As a substrate is being colonized with mycelium, heat is released a a by-product. After colonic on is complete, heat generation abates, and internal temperatures naturally dec :ie to nearly equal with air temperature. This s the i leal time to synchronize the other factors favor able to mushroom formation. Note that the temperature thresholds listed for each species are what cultivators call the bed. or substrate, temperature. Air temperature is adjusted upwards or downwards to affect the desired change When air temperature :s changec, a lag time follows, often for 24-72 hours, before the substrate temperature adjusts to he prerequisite level. In most cases, the critical temperature plateau occurs within 2-4 inches of the surface, the region supporting the ere a.ion of primordia.
Light: In nature, light acts as a signal alerting the mycelium to an open-air environment where, should mushrooms form, spores can be spread into the air. Light controls stem elongation and cap development. Ideal light conditions—intensity and wavelength—vary with each species and strain. Indirect natural light, or the dappled light filtering through a forest canopy, is considered ideal for woodland mushrooms. Specific photo-periods and spectral frequencies have not yet been established foi all mushroom species. In these cases, cultivators resort to providing the lighting necessary to the most sensitive of the gourmet mushrooms, the Pleurotus species. Modest light is not harmful to developing mushroom mycelium; it seems unaffected by its presence Direct sunlight or high intensity exposure is harmful The fluorescent lights used in indoor facilities do not inhibit mycelial growth, and in some circumstances may simulate early pri mordia formation. For most species, light levels between and 50-1000 lux and 380-480 nanometers ¿great! to blue) seem most stimulatory to primordia formation. (I use six 8 ft. long, "Daylight'" 6500 Kelvin fluorescents to light each 1000 sq. ft. growing room which also gets supplemental natural light through a row of diffusion panels.) For specific light requirements, please consult the growth parameters for the species being cul' wated.
Leatham and Stahlman (1987, 1989) con ducted trials with Shiitake on chemi :ally defined media which showed that the absence of calcium made the mycel:um unresponsive to light stimulation. At low calcium levels (< 40 ,1/g/mg) Shiitake myceiium formed mushrooms when stimulated by light between 600 680 nanometers or red light. At h'gh calcium (>130
Hg/mg.) levels, the wavelengths most stimulatory for primordia forma ; on were between 400-500 nanometers, what we know as blue to ultraviolet light. Calcium is naturally present in woods in sufficient quantifies to allow fruiting. Just as strains of Shiitake differ ;n their fruitir.g cycles, I suspect that the "calcium factor" in triggering Shiitake formation may be strain specific. Nevertheless, the interplay between light and calcium concentrations continues to be a subject of great interest. Further studies are needed to compare the many strains, on various woods, with vary' ig levels of calcium, and at different wavelengths.
The body of mycei:um is not as sensitive to these environmental stimuli until the substrate, its impending food source, has become fully captured by it. Where there are zones of uncolonized substrate, the mycelium continues on its conquest of nutrients, and fruitings are delayed until colonization is complete. Substrates that are carefully and evenly inoculated colonize faster, responding readily to the four environmental stimuli described above. When the rapidly growing mycelium is forced to stop because of natural borders or contact with competitors the mycelium shifts gears— biologically speaking—from conquest to consoli-dation. The mycelium consolidates its hold of the substrate by the infinite microscopic branching of hyphae. Concurrent with this phase change, the mycelium and the substrate cools. For Oyster mushroom cultivators, this period of declining temperature leads directly to primordia formation. At this juncture, the cultivator adjusts the surrounding environment—introducing light, dropping temperature exchanging air, and increasing moisture—to stimulate the greatest number of primordia.
Some mycologists take a different view of what causes this shift to fruiting in the mushroom life cycle. They describe the sudden lack of food for the mycelium as nutrient depri" 'ation. The best example of this is the Morel. Once the sclerotia have formed remote from the nutrient base, the nutrient base is physically separated from the sclerotial colonies, and this loss of nutrition is one of the triggers stimulating fruitbody formation. (This is basically the pivotal technique upon which the patent was awarded for growing morels—see Ower et al., 1978). In my mind, this is a clear case of true nutrient deprivation. However, substrate separation techniques are not generally used in the cultivation of Oyster, Shiitake Er oki, Lion's Mane, Maitake, Wood Ear and many of the
Initiation Temperature Chart
Days after Inoculation
♦ Bed Temperature ° Air Temperature
Figure 191. Chart of air vs substrate ("b,d") temperature during colomzafon. Not ^^¡Jffg^ r aturally declines as colonization is completed while air tempeature remams con:tant. An n,J^n strategy (i.e. droning temperature, adding moisture, increasing light and exchangmg a,r) ,s mst,gated to augment the mycelium's natural progression to fruiting.
other gourmet and medicinal mushrooms. More accurately, I would described these fruitings as being triggered by nut ient limitation, not deprivation.
Moisture: Atmospheric moisture must be carefully managed to allow mushroom development but not to the advantage of competitors While relative humidity approaches 100% during primordia formation, it should be lowered to levels whereby a constant rate of evaporation is drawn from the fruitbodies.The crop should be sprayed several times a day, as long as the excess water is soon reabsorbed by either the mushrooms, the substrate, or the air. This dynamic process of replenishment and loss encourages the best crops of mushrooms. The humidity in the growing room is often reduced several hours prior to picking, extending the shelf life of the crop. This is where the "Art" of cultivation plays a critical role in affecting quality.
Air Exchange: Air exchange and turbulence are managed for maximum benefit of the mushrooms, in terms of reducing carbon dioxide levels, elevating oxygen concentration, and to effect the constant evaporation of moisture from the surfaces of the maturing mushrooms.
Temperature\ Temperature levels either remain the same or are raised. Typ;:ally after primordia formation, temperature controls the speed of development of the fruitbody. Naturally, warmer temperatures result in faster growth while colder temperatures slow development. One advantage of fruiting at a cooler temperature is that a firmer-fleshed, higher-quality mushroom forms at the time of harvest,
Lighting: Without adequate light, stem elongation and malformation of the cap occur. Oyster and Enoki mushrooms are especially sensitive. Also strong light alters the pigment of the developing mushrooms. Some strains of Oyster mushrooms darken under bright light conditions; others pale. This response is also affected by temperature.
Duration: The timing of crops; their first appearance, the duration of harvest, and the period of time between crops are strain and process dependent. With Shiitake on sterilized sawdust/chips/bran, I go for 4 or 5 crops. With Oyster mushrooms grown in columns on pasteurized straw, two to three flushes seem most efficient. Approximately seven days to two weeks separate the end of the first flush to the beginning of the second. Fruiting occurs within time frames, or "windows of opportunities. "A period of dormancy is required between crops so nutrients can be accumulated as the mycelium prepares for the next crop. During these w' idows of opportunity, the cultivator must actively signal the mushroom mycelium with as many environmental stimuli as possible. Synchronizing this combination of events gives rise to the best possible fruitings.
The gilled mushrooms are tne archetypal forms we all recognize. They are typically umbrella shaped, with cylindrical stems and plates radiating outwards from the undersides of the caps. Oyster, Shiitake and Enold are classic gilled mushrooms. Taxonomically, these mushrooms fall into the Order Agaricales. Microscopically, they all produce spores by means of club-shaped cells called basidia.*
The most extensive treatise on the taxonomy of gilled mushrooms has to be Rolf Singer's Agaricales in Modem Taxonomy (1986). This massive work is the pivotal reference text on the overall systematics of fungal taxonomy. As the science of mycology progresses, individual monographs on a genus or a section of a genus delve more precisely into inter-species relationships. Alexander Smith's Mushrooms in their Natural Habitat (1949) still stands as the template for describing mushrooms macroscopically, microscopically and in their relationship to the natural environment. These two works, in combination, have had the greatest influence on the course of American mycology in the 20th century.
* For a discussion of basidia, consult Chapter 9. See Figures 47 to 52.
S^^AttSSaKSESBSSai cling, especially in the southeastern United States.
Common Names: The Black Poplar Mushroom The Swordbelt Agrocybe Yanagi-matsuiake (Japanese) Pioppino (Italian)
S out Poolar Mushroom or Zhuzhuang-Tiantougu (Chinese)
many inycq gists, is not as good as A, aegenta. More work on the taxa of the southeastern Agrocybes is needed.
Description: A substantial mushroom, often up to 12 inches in diameter. Cap convex, to hemispheric, expan^ ng to plane at maturity, smooth yellowish gray to grayish brown to tan to dingy brown, darker towards the center. Gills gray at first, becoming chocolate brown with spore maUrl ty. Stem wt lie, adorned with a well developed membranous ring, usually colored brown from spore fall.
Natural Habitat: Growing saprophytically, often in clusters, on stumps in the southeastern United States and southern Europe, deferring hardwoods, especially cottonwoods, willows, poplars, maples, box elders, and in China on tea-oil trees.
Distribution: Not known to occur in North America outside of the southeastern states of Mississippi, Louisiana and Georgia. Common across southern Europe anc1 in similar climatic zones of the Far East.
Microscopic Features: Spores smooth, ovci J to slightly ellipsoid, brown 9-11 x 5-6.5(7)/i, lacking a district germ pore. Clamp connections present
Available Strains: Strains are commonly available from culture libraries. Most strains cloned from wild specimens produce on hardwoods.
Mycelial Characte -st 's: Long udinally linear, becoming cottony, usually not aerial. White at first, soon becor ing spotted brown, and eventually tan brown Primordia usually form on malt extract agar media-
Fragrance Signature: Mealy, farinaceous, but not pleasant.
Natural Method ofl Cultivation: Stumps of the above-mentioned trees Outdoor wood chips beds also produce, much in the same manner as for the cultivation of Strophaiia rugoso-annulata
Recommended Courses for Expansion of Mycelial Mass to Achieve Fnrting: Petri dish cultures blended -'ia Eberbach stirrers to create iiquiu inoculum which is, in turn, injected into sterilized grain. This grain spawn can be used to make sawdust spawn for outdoor inoculations or for inoculating directly into supplemented, sterilized, hardwood sawdust.
Suggested Agar Culture Media: Malt Yeast Peptone Agar (MYPA), Potato Dextrose Yeast Agar (PDYA), OatmealYeast Agar (OMYA) & Dog FoodAgar (DFA).
1st, 2nd and 3rd Generation Spawn Media: Cereal grains (rye, wheat, milo, sorghum, etc.) for 1st
Figures 194-197. The Blade ropmr rnusnro,». u^ocybe aegerita) fruiting on supplemented alder sawdust/ chips 32, 33, 34 and 35 days after inocufc "on.
ana 2nd generation spawn. Sawdust is recommended for the 3rd generation, which can then be used to as spawn for inocu tion irec y into slices cut into stumps. Sa wdust spawn is also recommended for inoculation into sterilized, supplemented hardwood sawdust.
Substrates for Fruiting: I have fruity this species on supplemented oak and alder sawdust/chips Willow poplar, cottonwood. and raMalso support substantial fruitings.
Recommended Containers Polypropylene bags and trays. This mushroom is better grown from horizontal surfaces Mi im vertical ones. Yield Potentials: Up to 1 lb. of fresh mushrooms per 5-6 lb. block of sterilized sawdust/chips/bran " liven the si* uitings occur ' ng naturally, Jarge diameter willow, poplar and cottonwood stumps could sustain massive fruitings for many years.
Harvest Hints: A more fragile mushroom than it at first appears, this mushroom should be encouraged to gi w in clust ■ If mushrooms are harvested before the veils break, shelf-life is prolongeu.
Form of Product Sold to Market: Fresh, because of this mur^room's resemblance to the Button mushroom (Agaricus Lrunnescens) marketing is not as difficult as witn many "new" species.
Relative Humidity: 95-100%
Duration: 20-28 days
Fresh Air Exchanges: 0-1 per hour.
Light Requirements: n/a
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