Spore Ms Inoculation

The ultin'%^(^|cut for culturing mushrooms is via sfordJTnass/liquid inoculation directly into bulk substrates. Primarily used in China, this technique works well with Oyster and Shiitake mushrooms, but is also applicable to all the mushroom species discussed in this book. In effect this process parallels the technology of the brewery industry in the cultivation of yeasts- Saccharomyces cerevisiae and allies. Large fermentation vessels are filled with sugar broth, inoculated with pure spores and incubated and aerated via air compressors.

Spore mass inoculation of sterilized substrates is limited to those species which form mushrooms under totally sterile conditions. (Spores collected from wildly picked mushrooms have too many contain nants.) Those generating grain spawn 143

' I. " . '. I i. 1 -. . 'J.I 11 . ' . I.|.||__. ,, ___

Mushroom Spore Germinate And Form Hyphae

Figure 116. Scanning electron micrograph of spores in a frenzied state of spore germination.

Figure 117. Pressurized vessels in China designed for spore mass fermentation.

mushrooms that require the presence of microflora, such as the Button Mushroom (Agaricus 'o -unnescer^) and the King Stropharia (Otwpharia rugoso-annulata) are excluded. The key require ment is that the parent mushroom fruits on a sterilized substrate, wL! 'n a sterile environ ment, and sporulates abundantly. The following mushrooms are some of those which qualify All are wood or straw saprophytes. Agrocybe aegerita Flammulina velutipes Ganoderma hicidum and allies Lentinula edodes Pholiota r.ameko Pleurotus ci'rinopileatus Pleurotus djamor Pleurotus eryngii Pleurotus euosmus

Pleurotus ostreatus Pleurotus pulmonarius A practical approach is to first sterilize a half filled gallon of wood chips which is then inoculated with grain spawn. After several weeks of incubation, depending on the species, mushrooms form within the environment of the gallon jar. (Supplementation, for instance with rice bran, oatmeal or rye flour facilitates mushroom format1 on ) Once mature, the mushrooms are aseptically removed and immersed in sterilized water. Commonly the water is enriched with sugar-based nutrients and trace minerals to encourage rapid spore germination Millions of spores are washed into the surrounding broth. After \ :gorous shaking (a few seconds to a few minutes), the spore-enriched liquid is poured off into another sterile container, creating a Spore-Mass Master. Spores begin to germinate within minutes of

Figure 117. Pressurized vessels in China designed for spore mass fermentation.

Mycelium Pure Water
Figure 118. The fermented mycelium is tested for purity by siveaking sample droplets across a nutrient media filled petn dish. 48-72 hours later, pure colonies of mycelium (or contaminants) are easily visible.

contact with water. (See Figure 116). Immediately upon germination, and as the mycelium grows, respiration cycles engage. Therefore, the liquid broth must be aerated or the mycelium will be stifled. The method most used by the fermentation industry is aeration via oil-less compressors pushing air through banks of microporous filters. The air is distributed by a submerged aerating stone, a perforated water propellor, or by the turbulence of air bubbles moving upwards, as in a fish aquarium As the mass of the mycelium increases, and as the filters become clogged w;th airborne "dust," pressure is correspondingly increased to achieve the same rate of aeraion. The vessels must be continuously vented to exhaust volatile metabc'Jtes.

Each Spore Mass Master can inoculate 100 times its mass. For instance, if one removes a Shiitake mushroom, 4-5 inches in diameter, from ajar of sterilized sawdust, and then places that mushroom into a gallon of stenlized water, the spore-enriched broth, the Spore-Mass Master, can inoculate 100 gal Ions of nutrified liquid media. The functional range of expansion is 1:25 to 1:200 wkh a heavier inoculation rate always resulting ir. faster growth. After 2-4 days of fermentation at 75° F. (24° C.), a second stage of expansion can occur into enriched sterilized water, resulting in yet another 25-to 200-fold expansion of mycelial mass.

Success of the fermentation process can be checked periodically by streaking a 1/10th of a milliliter across a sterilized nutrient-filled petri dish and incubating for a few days. (See Figure 118). Additionally, contaminants can be immediately detected through odor and/or through examination of the liquid sample with a microscope. Any gases produced by bacteria or contaminants are easily recognizable, usu ally emitting uniquely sour or musty and sometimes sickeningly sweet scents.

The liquid spore mass inoculum can be transferred directly onto sterilized substrates such as grain, sawdust, straw, cottonseed hulls, etc. If the liquid inoculum is sprayed, even colonization occurs. If poured, the liquid inoculum streams down through the substrate, following the path of least resistance. Unless this substrate is agitated to distribute the mycelium, colonization will be uneven, resulting in failure.

T heoretically, the germination of spores in mass creates multitudes of strains which will compete with one another for nutrients. This has been long accepted as one of the Ten Commandments of Mushroom Culture. Scientists in China, whose knowledge had not been contaminated by such pre-conceptions, first

Culture Mushroom

Figure 119. Expanding mycelial mass using a combination of liquid fermentation and traditional grain-transfer techniques. After fermentation for 3-4 days, 100 quart (liter) jars of sterilized grain are liquid-inoculated. These are denoted as G1 Masters. In 7-10 days, lOOO-Vi gallon (2 liter) jars are inoculated from these G' masters. These are called G2. Then, 10,000 G3 gallon jars are inoculated from the G2's. Once grown through, 100,000 bags of sawdust spawn can be generated from the G3 jars. Each sawdust bag can be eApanded by a factor of 10 into supplemented sawdust, creating 1,000100 fruiting blocks. At 1-2 lbs. of mushrooms per block, more than 1,000,000 lbs. of mushrooms can be grown from one petri dish in as short as 80 days—depending ujion the species and strain.

Figure 119. Expanding mycelial mass using a combination of liquid fermentation and traditional grain-transfer techniques. After fermentation for 3-4 days, 100 quart (liter) jars of sterilized grain are liquid-inoculated. These are denoted as G1 Masters. In 7-10 days, lOOO-Vi gallon (2 liter) jars are inoculated from these G' masters. These are called G2. Then, 10,000 G3 gallon jars are inoculated from the G2's. Once grown through, 100,000 bags of sawdust spawn can be generated from the G3 jars. Each sawdust bag can be eApanded by a factor of 10 into supplemented sawdust, creating 1,000100 fruiting blocks. At 1-2 lbs. of mushrooms per block, more than 1,000,000 lbs. of mushrooms can be grown from one petri dish in as short as 80 days—depending ujion the species and strain.

developed spore-mass inoculation techniques to an industrial level. Only recently have Western mycologists recognized that a large community of spore matings behaves quite differently than paired individuals. San Antonio and Hanners (1984) are some of the first Western mycologists to realize that grain spawn of Oyster mushrooms could be effectively created via spore-mass inoculation.

The most aggressive strains out-race the least aggressive strains to capture the intended habitat. Recent studies have shown that these aggressive strains over-power and invade the cellular network of competing strains. Dr. Alan Rayner (1988) in studies at the University of Bath, described this form of genetic theft as "non-self fusions" between genetically different mycelial systems within the same species This ability to adapt has made fungi one of the most successful examples of evolution in the biological arena.

Spore-mass fermentation techniques are not yet widely used by North American or European cultivators. Concern for preserving strain stability, lack of experience, equipment, and intellectual conflict are contributing factors. In mushroom culture, intransigence to new ideas has prevailed, often because the slightest variation fromthenormhasresulted in expensive failures.

This method differs from the spore-mass inoculation techniques in that the starting material is dikaryotic mycelium, not spores. In short, the cultivator chops up the mycelium into thousands of tiny fragments using a high speed blender, allows the mycelium to recover, and transfers dilutions of the broth into jars or bags of sterilized grain. I prefer this technique as it quickly generates high quality spawn, eliminating several costly steps. Once perfected, most spawn producers find grain-to-grain transfers obsolete. The time not spent shaking the spawn jars frees the cultivator to attend to other chores. Most importantly, high-quality spawn is realized in a fraction of the time of the traditional methods. Step-by-step methods are described in the ensuing paragraphs. The ambient air temperature recommended throughout this process is 75° F. (24° C.).

Step 1. A vigorous, non-sectoring culture in cubated in a 100 x 15 mm. petri dish is selected. This parent culture is subcultured by transferring one-centimeter squares from the mother culture to ten blank petri dishes. In effect, ten subcultures are generated. The cultures incubate until the mycelia reaches approximately 1 cm. from the inside peripheral edge of the petri dish, more or less describing a 80 mm. diameter mycelial mat.

Step 2. When the cultures have achieved the aforementioned growth, use the following formula to create a liquid culture media: After mixing and subdividing 750 ml. of the broth into three 1500 ml. Erlenmeyer flasks, the vessels are placed within a pressure cooker and sterilized for 1-2 hours at 15 psi (252° F. -121° C.)*

1 With experience, the cultivator will likely want larger vessels for fermentation. I prefer a 5000-7000 ml. squat glass flask, into which 2250 ml. of liquid culture media is placed, sterilized, and inoculated with 750 ml. of liquid inoculum. When the liquid volume exceeds 5000 ml. additional measures are required for adequate aeration, such as peristaltic pumps pushing air through media filters. The surface area of the liquid broth should be at least 110 mm./ 2000 ml. for sufficient transpiration of gases and metabolic by-products.

Manufacturing Sandwich Composites

Figure 120. Actively growing mycelium 6 and 12 hours after inoculation.

Figure 120. Actively growing mycelium 6 and 12 hours after inoculation.

Stamets' Liquid Culture Media for Wood Decomposers

1000 ml. water 40 grams barley malt sugar 3-5 grams hardwood sawdust 2 grams yeast 1 gram calcium sulfate

Place a floating stir bar into each Erlenmeyer flask. The openings should be stuffed tightly with non-absorbent cotton and covered with aluminum foil.77z<? ingredients do not dissolve ThepHfalls between 6.0-6.5 when using near neutral water at make-up First, a 1000 ml. Eberbach stirrer is filled with 750 ml. of water and sterilized. Simultaneously, three 1500 ml. Erlenmeyer flasks, each containing 750 ml. of the above concoction, are sterilized. After sterilization, the pressure cooker naturally cools. If your pressure cooker does not form a vacuum upon cooling, then the Eberbach stirrer and the Erlenmeyer flasks must be removed at 1-2 psi., before reaching atmospheric pressuie. Otherwise, contaminants are drawn in. The slightest mistake with this process could ruin every tiling that is inoculated downstream. If the pressure cooker does achieve negative pressure, the vacuum must be broken paying careful

Master Mushroom Spawn
Figure 121. Free-pouring of fermented mushroom m celium into sterilized grain to create Grain Spawn Masters.

attention to the path by which air is drawn in. The outer surface of the pressure cooker should have been wiped clean and placed into the airstream coming from the laminar flow ber_ch. Since the airstream coming from the face of the micron filter is free of airborne particulates, the media remains sterile. Additionally, I like to saturate a sterilized cotton cloth (cotton baby diapers work well) with isopropanol and place it over the vent valve as an additional precaution. When the stop-cock is opened, clean air is drawn through the alcohol-saturated cloth. Once the pressure returns to normal, the pressure cooker is opened into the airstream. with the leading edge nearest to the filter. The contents are removed and allowed to cool.The cultivator should always remain conscious of the cleanliness of the surfaces of the pressure cooker, his hands, and the countertops upon which items are placed.

Step 3. Of the ten cultures, the five best are chosen. Any culture showing uneven growth, sectoring, or any abnormality is viewed with suspicion and is excluded. The mycelium from each petti dish is sectioned into quadrants with a heat-sterilized scalpel and asepticgly transferred into the Eberbach stirrer containing the sterilized water. Heat sterilization of the scalpel need only occur once. This is the single step hat is most dependent upon the actions of the laboratory technician. Since five cultures are cut and transferred, the slightest mistake at any time will allow contamination to be passed on, thereby jeopardizing the entire run. Should the scalpel touch anything other than the cultured mycelium, it should be re-sterilized before continuing. Once the transfers are complete, the screw-top lid of the Eberbach is replaced carefully adhering to the principles of standard sterile technique

Step 4. The Eberbach stirrer is placed on the power unit and stirred in 3-second bursts. (The blender I use rotates at 8400 rpm.) Pausing for 5 seconds, the surviving chunks of agar fall downwards into the blades. Another 3-second burst decimates these pieces. One more 5-sec-ond pause is followed by the last 3-second, high-speed stir. In effect, the stirring process has created thousands of chopped strands of mycelium, in short cell chains.

Step 5. The water/mycelium blend is trans-fened! 250 ml. at a time in equal proportions, into the three 1500 ml. Erlenmeyers. A remote ' syringe, pipette, or liquid pump can be used. Less elaborate is to simply "free-pour" equal volumes of myceliated fluid from the Eberbach into each Erlenmeyer. The non-absorbent cotton stoppers are, of course, removed and replaced with each pouring, being careful not to allow contact between tb e cotton stopper and becomes its own universe, hosting thousands of star-shaped, three dimensional colonies of mycelium. This i, the stage idealfo, inoculation into sterilized substrates, especially in the generation of grain spawn masters. (See Figure 120). Far more bioactive ±an the same mycelium transferred from the two-dimensional surface of a petri dish, each hyphal cluster grows at an accelerated i ate subsequent to transfer to the grain media.

If however, the liquid media is not used at its peak rate of growth, and stirs for nearly a week, the colonies lose their independence and coalesce into a clearly visible contiguous mycelial mat. Long mycelial colonies adhere to the inter face of the fluid surface and the inside of the flask. Chains of mycelium collect downstream from the direction of rotation. Soon after their appearance, often overnight, the mediabecomes translucent and takes on a rich amlier color. A large glob of mycelium collects on the surface and can be mechanically retrieved with a pair of tweezers, forceps, or scalpel, if desired. The re maining clear amber fluid contains super-fine satellite colonies and hyphal fragments. By parsing the fluid through a microporous filter, the myce'ium can be recaptured. This technique is espec ially attractive for those whose goal is running tests on small batches of mycelium With many species I have grown, the conversion ratio of sugar/wood to mycelium (dry weight) approaches 20%. This percentage of conversion is nearly 80% biolog: al efficiency, considered good in the commercial cultivation of gourmet mushrooms.

Step 6 Each of the three Erlenrrieyer flasks now contains 1000 ml. of nutrient, mycelium-~chbroth.At30ml.pertransfer, 100 1/2 gallon (2 liter) grain-filled jars can be inoculated. Here too, a pipette, back-filled syringe burette, or pump can be used. I prefer "free-pouring" 30

Figure 122. Inoculating mycelium into an Eberbach holding sterilized water.

any contaminated surface. Each Erlenmeyeris placed on stiT olates or on a shaker table and rotated at 100- 200 rpm. for 48-72 hours. The water broth is continuously stirred to allow transpiration of metabolic gases and oxygen absorption. The fluid has a milky-brown color and is not translucent. Settling of the heavier components is clearly visible when the stirring process is interrupted.

Upon completion, 3000 milliliters of mycelium are rendered in liquid form. The hyphae, recovering from the damage of being cut by the spinning blades of the blender, are stimulated into vigorous re-growth. At a point several cells away from the cut ends, nodes form on the cell walls, new buds push out, and branch. A vast, interconnected fabric of cells, a mycelial network, forms The branches fork continuously. After two to four days of re-growth in the nutrient enriched broth, each Erlenmeyer flask

Mushroom Cultivation Ventilation
Figure 123. A space-efficient rack for incubating ? -ain spawn in jars. 3401/2 gallon jars can be store 1 or this 8' long x 8 high x 16" wide shelf system Spawn quality is improved by storing the jars at an i ngle. (Earthquake sensitive.)

ml. of myceliated broth directly out of eac ti Eilenmeyer into each half gallon jar of sterilized grain. In time, an adept cultivator deve >ps a markably accurate ability to dispense li i spawn in consistently equal proportion* The spawn maker's movements become rapid, repetitious, and highly rhythmic *

One study, using a similar method (Yang and Yong 1987), showed that the hyphal clusters averaged less than 2 mm. in diameter, and that each milliliter contained 1000-3500 "hyphal balls." The range of time for the maximum production of hyphal clusters varied between species, from two days to fourteen Tb . recommended inoculation rate was 15 ml. for |a<H 250 grams of grain, For ease of handling, distribution and colon: nation, I find that the dilution schedule described above efficiently inoculates large volumes of grain in the creation of grain masters. (30 ml. of inoculum is used to inoculate 500-600 grams of grail in 2-liter or 1/2-gallon jars). Most of the wood decomposers described in this book flourish with the aforementioned technique.

The lids to each container are replaced as soon as they are inoculated. If the lids to each jar are loosened prior to free-pouring, then one hand lifts each lid, while the other hand, pours the liquified mycelium into each jar, moving side-to-side. If an assistant is present, the jars are removed as soon as they arc inoculated. A s they are removed each lid is tightly securec and the ' ft is quickly shaken to evenly mix the li(. uid pawn through the grain. Each jar is stored at an ngle on a spawn rack. One person mom-Mini in this fashion can keep two people busy "feeding" himnew jars and removing those just inoculated. Since this system is fast p iced the time vector, the "window of vulnerability," is much less compared to the time-consuming, taker-intensive, traditional methods. The disadvantage of this technique, if there is one, is that the stakes for the clumsy spawn ro< ucer are higher. Any mistake will be amplilie< with force. ;hould any one of the petri dish cultures harbor contaminants, once that culture is placed together in the Eberbach stirrer, all resulting spawn jars will be contaminated. This is an all-or-nothing technique Fortunately, if following the techniques outlined in this book, success is

* Various laboratory pumps can be used for highly accurate injections of liquid med without danger o contamination.The Monostat Jr. Dispenser ® I'1947-110), equipped with a foot switch, dt 'lvers lots of 10-50 ml. of liquid inccula per secon utilizing a 5/16 in. silicon tube. If equipped with a multif : dispersion manifold, several spawn containers hi once can be inoculated with ease and speed.

the norm.

The jars normally grow out in 4-7 days, many times faster than the traditional transfer technique And the jars are only shaken once—at the time of liquid inoculation. With the traditional wedge-transfer technique, each individual jar must be shaken two or three times to insure full colonization: first at inoculation; second after three days; and finally at days 5,6 or 7. Remember, not only is the cultivator gaining efficiency using the liquid inoculation method but 100 Grain Masters are created in a week from a few petri dish cultures. With less need for shaking, hand contact with the Grain Masters is minimized. Time is conserved. Probability of contamination is reduced. Growth is accelerated. With each kernel, dotted with stellar clusters of hyphae from the first day of inoculation, spawn quality is greatly improved.

As with any method described in this book, quality controls must be run parallel with each procedure. A sample of the mycelium-enriched broth is drop-streaked across the surface of a few nutrient-agar filled petri dishes. (See Figure 118). These will later reveal whether the liquid contains one organism—the mycelium—or a polyculture —the mycelium and contaminants. Furthermore, one or more of the sterilized grain-filled j; rs should be left unopened and uninoculated to determine the success of the sterilization procedure. These "blank" vessels should not spontaneously contaminate. If they do, then either the stei "Nation time/pressure was insufficient or airborne contamination was introduced, independent of the liquid fermented spav/n. If the jars injected w;th the fermented mycelium contaminate, and the uninoculated controls do not, then obviously the vector of contamination was related to the act of inoculation, not the cycle of grain sterilization. (See Chapter 10: the Six Vectors of Contamin?fion).

Trends in spawn technology are evolving towards pelletized spawn. Pelletized spawn is specifically designed to accelerate the colonization process subsequent to inoculation. Examples of pelletized spawn range from a form resembling rabbit food to pumice-like particles. In either case, they are nutrient-saturated to encourage a burst of growth upon contact with mushroom mycelium. Pelletized spawn vanes in size from 1 mm. to 5 mm. in diameter.

Pelletized spawn can be made by adapting pelletized food mills designed for the manufacture of animal feeds. With modest reengineering, these machines can be modified to produce spawn pellets. Idealized spawn seeks a balance between surface area, nutritional content, and gas exchange. (See Yang and Jong 1987; Xiang, 1991; Romaine and Schlagnhaufer, 1992.) A simple and inexpensive form of pelletized spawn can be made from vermiculite saturated with a soy protein-based nutrient broth.

The key to the success of pelletized spawn is that it enables easy dispersal of mycelium throughout the substrate, quick recovery from the concussion of inoculation, and ideally, the sustained growth of mycelium sufficient to fully colonize the substrate. Many grains are, however, pound-for-pound, particle-for-par-ticle, more nutritious than most forms of pelletized spawn.

I believe the spawn should be used as the vehicle of supplementation into a semi-selective substrate. Others subscribe to the school of thought that the substrate's base nutrition should be raised to the ideal prior to spawning The danger with this approach is that, as the base nutrition of the substrate is raised, so to is its receptivity to contan inants. From my expe riences, using a nutrition panicle already encapsulated by mushroom mycelium s more successful. The ultimate solution may be a hybrid between liquid inoculum and grai. spawn: a semi-solid slurry millimeters in diameter which would maximally carry water, nutnents, and mycelium.

Once spawn has been created, the cultivator arrives at a critical crossroad in the mushroom cultivation process. Several paths can be pursued for the growing of mushrooms, depending on the species and base materials. Some of these paths are] intrinsically unproblematic; others are not. Success is measured by the following criteria: speed and quality of colonization, crop yield and resistance to disease.

The first step can be the most critical. When trying to match a mushroom strain with an available substrate, I place a small sample of the substrate into the agar media formula. Upon exposure, the mushroom mycelium generates enzymes and acids to break down the proposed food source Once acclimated, the mycelium carries a genetic memory of the end subs' ate to which it is destined. With Shiitake, Enokitake, Maitake, and Reishi, I acquaint tt e mushroom mycelium with the host substrate by introducing to the media a 1-2 gram sample of the sawdust directly into the liqu id ferment; ition vessels. This liquid inoculum is then used to generate grain spawn. I am convinced that this method empowers the mushroom mycelium.

Grain spawn can be used for direct inoculation into pasteurized straw, into sterilized sawdust, or into enriched sawdust. If growing Oyster mushrooms, the recommended path is to inoculate straw with grain spawn. If one wants to create plug spawn for the inoculation of stumps and logs, the best path is to go from grain spawn to sterilized sawdust, and once grown-out, to sterilized wooden dowels. I Drthe rapid, high-yield methods of growing Shiitake, Enokitake intake, Kuritake and others indoors cm stetapied substrates, I recommend the followilnSJjgoingfrom grain spawn to sterilized SfRli' ! to enriched sawdust. Each transfer step results in an expansion of mycelial mass, usually by a factor of 5-10 and takes a week to two weeks to fully colonize.

The tracks recommended in the previous paragraph are the result of thousands of hours of experience. More direct methods can be used, but not without their risks. For instance, one can use grain spawn of Shiitake to inoculate enriched sawdust, skipping the above-described intermediate step of sawdust However, several events are observed subL.-quent to inoculation. First, there are noticeably fewer points of inoculation than if sawdust spawn was used. As a result, recovery is slower and colonization is not as even. ("Leap off' is faster from sawdust spawn than from grain spawn. The mycelium has already acclimated to the sawdust substrate.) Most importantly, a marked increase in temperature occurs soon after inoculation known by mushroom cultivators as thermo gene sis. (See page 55). By enriching the substrate with grain spawn, increasing its nitrogen content, biochemical reactions are accelerated, and correspondingly two main by-products: heat and carbon dioxide. Should internal temperatures exceed 100 . (38° C.) in the core of each bag, latent contaminants, especially thermophilic bacteria and black pin molds (Aspergillus, Rhizopus, and Mucor) spring forth, contaminating each and every bag. These same bags, incubated at 75 F. (24 C.) would otherwise be successfully colo-

Oyster Mushroom Mycelium Grains
Figure 124. Oyster mushrooms "breaking out" of a jar filled with grain spawn an event with potentially disastrous consequences for the laboratory.

nized with mushroom mycelium. In general, the cultivator should assume that a minor population of contaminants will survive "sterilization" especially as the mass of each batch increases. Thermotolerant contaminants are activated when temperatures within the substrate spiral upwards .To thwart this tragedy, the bags containing nitrogenous supplements should be spaced well apart when placed on open wire rack shelving. The laboratory manager should carefully monitor air temperature to off-set the upwardly spiralling trend of internal temperatures.

This arena of problems is largely avoided by using sawdust spawn for inoculation into supplemented sawdust substrates rather than grain spawn.Thermogenesis is reduced to a more man ageable level. Colonization is faster, more even, and one gets more "mycelial mileage" from grain spawn by generating intermediate sawdust spawn.

— —— ir m^mmmwm —nw* —e——em - mms b^eb r^r1

In essence, another exponent of expansion of the mycelial mass has been introduced to the benefit of overall croduction.

In contrast, grain spawn is preferred over sawdust spawn for the cultivation of Oyster mushroom on cereal straws. Grain spawn boosts the nutritional base of straw, radically improving yields compared to using an equal mass of sawdust spawn. Although sawdust may have more points of inoculation, yields are substantially less than if the straw had been :mpregnated with grain spawn. Two exceptions are Hypsizygus ulmarius and H. cessulatus, both of which benefit when sawdust spawn is used to inoculate wheat straw.

In Chapter 21, the growth parameters of each species and the recommended courses for matching spawn and substrate for maximizing yields and minimizing problems are described in detai!

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