Structure of the Habitat

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Whichever materials are chosen for making up the substrate base, particular attention must be given to structure. Sawdust is uniform in particle size but is not ideal for growing mushrooms by itself. Fine sawdust is "closed" which means the particle size is so small that air spaces are soon lost due to compression. Closed substrates tend to become anaerobic and encourage weed fungi to grow.

Wood shavings have the opposite problem of fine sawdust. They are too fluffy. The curls have large spaces between the wood fibers. Mycelium will grow on shavings, but too much cellular energy is needed to generate chains of cells to bridge the gaps between one wood curl and the next. The result is a highly dispersed, cushionlike substrate capable of supporting vegetative mycelium, but incapab'e of generating mushrooms since substrate mass lacks density.

The ideal substrate structure is a mix of fine and large particles. Fine sawdust particles encourage mycelia to grow quickly. Interspersed throughout the fine sawdust should be larger wood chips (1-4 inches) which figure as concentrated islands of nutrition. Mycelium running dirough sawdust is often wispy in form until it encounters arger wood chips, whereupon the mycelium changes and becomes highly aggressive and ihizomorphic as it penetrates through the denser woody tissue. The structure of the substrate affects the design of the mycelium network as it is projected. From these larger island-like particles, abundant primordia form and can enlarge into mushrooms of great mass.

For a good analogy for this phenomenon, think of a camp fire or a wood stove. When you add sawdust to a fire, there is a flare of activity which soon subsides as the fuel burns out. When you add logs or chunks of wood, the fire is sustained over the long term. Mycelium behaves in much the same fashion.

Optimizing the structure of a substrate is essential for good yields. If you are just using fine sawdust and wood chips (in the 1-4 inch range) then mix 2 units of sawdust to every 1 unit of wood chips (by volume). (Garden shredders are useful in reducing piles of debris into the 1-4 inch chips.)

Although homogeneity in particle size is important at all stages leading up to and through spawn generation, the fruitbody formation period benefits from having a complex mosaic of substrate components. A direct relationship preva; ; between complexity of habitat structure and health of the resulting mushroom bed.

A good substrate can be made up of woody debris, chopped corncobs and cornstalks, stalks of garden vegetables, vines of berries or grapes. When the base components are disproportionately too large or small, without connective particles, then colonization by the mushroom mycelium is hindered.


Mushroom straps vary in their ability to convert substrate materials into mushrooms as measured by a simple formula known as the "Biological Efficiency (B. E.) Formula" originally developed by the White Button mushioom industry. This formula states that

3 1 lb. of fresh mushrooms grown from 1 lb. of dry substrate is 100% biological efficiency.

Considering that the host substrate is moistened to approximately 75% water content and that most mushrooms have a 90% water content at harvest, 100% B. E. is also equivalent to '

□ growing 1 lb. of fresh mushrooms for every 4 lbs. of moist substrate, a 25% conversion of wet substrate mass to fresh mushrooms or

□ achieving a 10% conversion of dry substrate mass into dry mushrooms.

Many of the techniques descried in this book will give yields substantially higher than 100% B. E. Up to 1/2 conversion of wet substrate mass into harvestable mushrooms is possible. (I have succeeded in obtaining such vields with sets of Oyster Shiitake, and Lion's Mane. Although 250% B. E. is exceptional, a good grower should operate within the 75125% range.) Considering the innate power of the mushroom mycelium to transform waste products into highly marketable delicacies, it is understandable why scientists, entrepreneurs, and ecologists are awestruck by the prospects of recycling with mushrooms.

Superior yields can be attained by carefully following the techniques outlined in this book, paying strict attention to detail, and matching these techniques with the right strain. The best way to improve yields is simply to increase the spawn rate. Often the cultivator's best strategy is not to seek the highest overall yield. The first, second, and third crops (or flushes) are usually the best, with each successive flush decreasing. For indoor cultivators, who are concerned with optimizing yield and crop rotation from each growing room, maximizing yield indoors may incur unacceptable risks. For instance, as the mycelium declines in vigor after several flushes, contaminants begin to flourish. Future runs are quickly imperiled.

If growing on sterilized sawdust, I recommend removing the blocks after the third flush to a specially constructed four sided, open-air nettea growing room.This over-flow or"yield recapture" environment is simply fitted with an overhead nozzle misting system. Natural air currents provide plenty of circulation. These recapture buildings give bonus crops anc require minimum maintenance. Growers ;n Georgia and Louisiana have perfect climates for this al

Byproducts of Straw Substrate Due to Conversion by Pleurotus ostreatus

Figure 39. Chart showing comparison of by-products generated by Oyster (Pleurotus ostreatus) mycelium's decomposition of wheat straw. (Adapted from Zadrazil (1976))

Carbon Dioxide nnm Water MBB Mushrooms EFÜ Residual Compost

ternative. Subtropical regions of Asia are similarly well suited. (For more information, see Appendix I.)

Biological efficiency depend :3Jpon the stage of mushrooms at harveslj. mushrooms ("buttons") are generallyWme Electable and store better. Yet if the entire crfep is picked as buttons, a substantial loss in yield potential (B. E.) occurs. Mature mushrooms, on the other hand, may give the cultivator maximum biological efficiency, but also a crop with a very short shelf life and limited marketability.

Each species passes through an ideal stage for harvesting as it matures. Just prior to maturity, features are transformed through the re-proportionment of cells without any substantial increase in the total weight of a mushroom as it matures. This is when the mushroom margins are decurved (pointing downwards) or slightly incurved, and well before spore generation peaks. Overtime, cultivators learn the ideal stage for harvest.

Figure 40. Lillian Stamets holdin; bag of commercial Agaricus brunnescens spawn.


pawn is any form of mycelium that can be dispersed and mixed into a substrate. For most would-be cultivators, the easiest way j to grow mushrooms is to buy spawn from a company and mix it j (inoculate) into a substrate. Spawn can be purchased in a variety of j forms. The most common forms are grain or sawdust spawn. Grain j spawn is typically used by commercial cultivators to inoculate steril- | ized or pasteurized substrates. The White Button industry traditionally ! depends on highly spec' ilized compani< :s, often family-owned, which 1 have made and sold spawn for generations

Most amateurs prefer buying spawn because they believe it is easier than generating their own. This is not necessarily the case. Because spawn is a living organism, it exists precariously. Spawn remains in j a healthy state for a very limited period of time. Usually after 2 months, even under refrigeration, a noticeable decline in viability occurs. After this "honeymoon" period, spawn simply over-matures |

for lack of new food to digest. The acids, enzymes, and other waste products secreted by the mushroom mycelium become self-stifling. As the viability of the spawn declines, predator fungi and bacteria exploit the rapidly failing health of the mycelium. A mycelial malaise seizes the spawn, slowing its growth once sown onto new substrates and lowering yields. The most common diseases of spawn are competitor molds, bacteria, and viruses. Many of these diseases are only noticeable to experienced cultivators.

For the casual grower, buying commercial spawn is probably the best option. Customers of commercial spawn purveyors should demand: the date of inoculation; a guarantee of spawn purity; the success rate of other clients using the spawn; and the attrition rate due to shipping. Spawn shipped long distances often arrives in a state very different from its origi nal condition. The result can be a customer-relations nightmare. Ibelieve the wisest course is for commercial mushroom growers to generate their own spawn. The advantages of making your own spawn are:

1. Quality control: With the variable of shipping removed, spawn quality is better assured. The constant jostling breaks cells and wounds the spawn.

2 .Proprietary Strain Development: Cultivators can develop their own proprietary strains. The strain is the most important key to success. All other factors pale in comparison.

3. Reduction of an expense: The cost of generating your own spawn is a mere fraction of the price of purchasing it. Rather than using a spawn rate of only 3-6% of the mass of the to-be-inoculated substrate, the cultivator can afford to use 10-12+ % spawning rates.

4. Increasing the speed of colonization. With higher spawning rates, the window of opportunity for contaminants is significantly narrowed and yields are enhanced. Using the spawn as the vehicle of supplementation is far better than trying to boost the nutritional base of the substrate prior to inoculation.

5. Elimination of an excuse for failure. When a production run goes awry, the favorite excuse is to blame the spawn producer, whether at fault or not. By generating your own spawn, you assume full responsibility. This forces owners to scrutinize the in-house procedures that led to crop failure. Thus, cultivators who generate their own spawn tend to climb the learning curve faster than those who do not.

6. Insight into the mushroom life cycle. Mycelium has natural limits for growth. If the spawn is "over-expanded", i. e. it has been transferred too many times, vitality falters. Spawn in this condition, although appearing healthy, grows slowly and often shows symptoms of genetic decline. A spawn producer making spawn for his own use is especially keen at using spawn at the peak of its vitality. These insights can not be had by those who buy spawn from afar.

Fruitbody Development


J hen a collector finds mushrooms in the wild, the encounter is a mere coincidence, a "snap-shot" in time of a far vaster process. The mushroom life cycle remains largely invisible to most mushroom hunters; not so to cultivators. The mushroom cultivator follows the path of the mushroom life cycle from beginning to end. Only at the completion of the mushroom life cycle, which may span weeks or months, do mushrooms appear, and then they occur for but a few days. The stages leading up to their appearance remains fascinating even to the most sagacious mycologists.

For mushrooms to survive in our highly competitive world, where legions of other fungi and bacteria seek common ecologial fjioies, millions of spores are often produced per mushroom. With the larger agarics, the numbers become astronomical. Since mushrooms reproduce through spores, the success of the mushroom life cycle depends upon their production.

establishing their own territo: lal domains. In this sense., spores from one mushroom can actually compete wiih one another for the same ecological niche.

Each mushroom is like an island. From this center, populations of spores decrease with distance. When spores germinate, the mycelium grows out radially, away from the site of origin. Often times, the next hospitable environment may be far away. Spores, taken up by the wind, or carried by insects and mammals, are dispersed to habitats well distant from the parent mushroom. By coincidence, different varieties of the same species meet and exchange genetic material. In the ever-changing ecoiogical land -scape, new varieties are favorably selected for and survive. This diversity within a species is critical to preserving its ability to adapt

Enzymes and acids are secreted by the mushroom mycelium into the surrounding en-

Each spore that is released possesses one half of the genetic material necessary for the propagation of the species. Upon germination, a filamentous cell called a hypha extends. Hy-phae continue to reproduce mitotically. Two hyphae, if compatible, come together, fuse and combine genetic material.The resuk' ig mycelium is then described as being binucleate and dikaiyotic. After this union of genetic material, the dikaiyotic mycelium accelerates in its growth, again reproducing mitotically. Mated mycelium characteristically grows faster than unmated mycelium arising from single spores.

The mating of compatible hyphae is geneti cally determined. Most of the gourmet species are governed by two incompatibility factors (A and B). As a result only subsets of spores are able to combine with one another. When spores germinate, several strains are produced. Incom • Figure 43 Sclerotj-' of Pleuroius tuber-regium. patible strains grow away from each other,

Figure 42. Scierotia of Psilocybe mexicana.
Mycelium Texture Tileable
Figure 44. Scanning electron micrograph of mycelium.

vironment, bracking down lignin-cellulose complexes into simpler compounds.The mushroom mycelium absorbs these reduced organic molecules as nuti- nts directly through its cell walls. After one mushroom species has run its course, the partially decomposed substrate be comes available to secondary and tertiary saprophytes who reduce it further. Ultimately, a rich soil ;s created for the benefit of plants and other organisms.

As the mycelium expands, a web of cells is formed, collectively called the mycelial net work. The arrangement of these cells is designed to optimally capture an ecological niche. Species differ in the manner by which the mycelial mat is projected. Initially, Morel mycelium throws a thinly articulated mycelial network. (Morel mycelium is the fastest-growing of any I have seen. ) Once a substantial territorial donr'n has been over-ran, side branching of the mycelium occurs, resulting in a thickening of the mycelial mat

W ith the approach of winter, the mycelial mat retreats to survive in specific sites. At this time, many mushrooms, both gilled and non-gilled, producesclerotia. Sclerotia are a resting phase in the mushroom life cycle. Sclerotia resemble a hardened tuber, wood-like in texture (See Figures 42 and 43.)While in this dormant state, the mushroom species can survive m clement weather conditions like drought, fire, flooding, or other natural catastrophes. In the spring., the sclerotia swell with water and soften. Directly from the sclerotia, mushrooms emerge Morels are the best known mushrooms which arise from sclerotia. (See Figures 359 360). By the time you find a mature Morel, the sclerotia from wLch it came will have disappeared.

Most saprophytic mushrooms produce a thick mycelial mat after spore germination. These types of mycelial mats are characterized by many cross-overs between the hyphae. When two spores come together and mate, the down stream mycelium produces bridges between the cells, called clamp connections Clamp connections are especially useful for cultivators who want to determine whether or not they have mated mycelium. Mycelium arising from a single spore lacks clamp connections entirely, and is incapable of producing fertile mushrooms

As the mycelial network extends, several byproducts are produced. Besides heat, carbon dioxide is being generated in enormous quantities. One study (Zadrazil, 1976) showed that nearly 50% of the carbon base in wheat straw is liberated as gaseous carbon dioxide in the course of its decomposition by Oyster mushrooms! 10% was converted into dried mushrooms 20% was converted to proteins. Other by-products include a variety of volatile alcohols, ethylenes, and other gases. (See ] figure 39.)

While running fhrough a substrate, the mycelium is growing vegetatively. The vegetative state represents the longest phase in the mushroom life cycle. The substrate will continue to be colonized until physical boundaries prevent further growth or a biological competitor is encountered. When vegetative colonizaron ceases, the mycelium enters into temporary stasis. Heat and carbon dioxide evolution decline, and nutrients are amassed within the storage vestibules of the cells. This resting period is usually short-lived before entering into the next phase

From the natural decliiff in temperature within the host substrate, as well as in response to environmental stimuli (water and humidity, light, drop in temperature, reduction in carbon dioxide, etc.), the mushroom mycelium is trig gered into mushroom production. The

Figure 45. Primordia form and enlarge.

Figure 46. A miniature mushroom emerges from the mycelial plateau.

Figure 45. Primordia form and enlarge.

Figure 46. A miniature mushroom emerges from the mycelial plateau.

mechanism responsible for this sudden shift from active colonization to mushroom forma tion is unknown, often being referred to as a "biological switch." The mosa;c of mycelium, until now homogeneously arranged coalesces into increasingly dense clusters. (See Figure 45). Shortly thereafter—literally minutes with some species—these hyphal aggregates form into young primordia. (See Figure 46), In quick succession, the first d'scernible differentiation of the cap can be seen.

The period of primordia formation ' 5 one of the most critical phases in the mushroom cultivation process. Both mycelium and cultivator must operate as a highly coordinated team for maximum efficiency. Bear in mind that it is the mycelium that yields the crop; the cultivator is merely a custodian. The duratk n for primordia formation can be as short as 2 days or as long as 14. If managed properly, the microscopic land scape, the mycosphere, will give rise to an even, high-density population of rapidly forming pn mordia. Visible to the naked eye, the mycelium's surface is punctuated with a lattice-work of valleys and ridges upon which moisture droplets continually form, rest, and evaporate. In the growing room this per xl corresponds to 98-100 % rH, or a condensing fog. Even in a fog, air currents have an evaporative effect, drawing moisture to the surface layer. The careful management of this mycosphere, with high oxygen, wicking, evaporation, and moisture replenish ment combined with the effect of other environmental stimul: results in a crescendo of primordia formation. Cultivators call these environmental stimuli, collectively, the initiation strategy

Primordia. once formed, may rest for weeks, depending upon the species and the prevailing environment. In most cases, the primordia ma

Figure 47. As the basidia mature, sterigmata project from the apices.
Fi gire 48. Scanning electron micrograph of young basidium

ture rapidly. Rhizomorphs, braided strands of large diameter hyphae, feed the burgeoning primordia through cytoplasmic streaming. The cells become multinucleate, accumulating ge netic material. Walls orseptae form, separating pairs of nuclei, and the cells expand, resulting in an explosive generation of mushroom tissue.

As the mushroom enlarges, differentiation of familiar features occurs. The cap, stem, veil, and gills emerge. The cap functions much like an umbrella, safeguarding the spore-producing gills from wind and rain. Many mushrooms grow towards light .A study by Badham (1985) showed that, with some mushroom species (; e. Psilocybe cubensis), cap orientation is foremost affected by the direction of air currents, then by light, and finally by gravity. Beneath the cap, the gill plates radiate outwards from a centralized stem like spokes on a wheel

Over the surface of the gills, an evenly dis-

Figure 49. At each tip of the stengmaia, a spore cavity forms.

persed population of spore-producing cells called basidia emerge. The basidia arise from a genetically rich dense surface layer on the gill called the hymenium The gill trama il nestled between the two hymenial layers and is composed of larger interwoven cells, which act as channels for feeding the hymenial layers with nutrients. (See Figure 53). When the mushrooms are young, few basidia have matured to the stage of spore release. As the mushrooms emerge, increasingly more and more basidia mature. The basidia are club-shaped, typically with four "arms" forming at their apices.These arms, thcsterigmata, project upwards, elongat ing. (See Figures 47 and 48). In time, each tip swells to form small a globular cavity which eventually becomes a spore. (Figure 49).

Initially, the young basidia contain twc hap loid, sexually paired nuclei. They fuse, in a process known as karyogamy, to form one diploid nucleus containing a full complement of

Figure 50. Populations of basidia evenly emerge from the gill plane.
Figure 51. A fully mature basidium. Note germ pores at open ends of spores.

chromosomes. Immediately thereafter, meiosis or reduction division occurs, resulting in four haploid nuclei.The haplc! i nuclei are elastic in form, squeezing up the sterigmata to be deposited in their continually swelling tips. Once resid:~g in the newly forming spore cavity, the spore can: lg enlarges Each spore is attached to the end of each sterjma by a nipple-lill protuberance, called the sterigmal appendage. With many species, the opposite end of the spore is dimpled with a germ pore. (See Figure 51).

The four spores of the basidia emerge diametrically opposite one another. This arrangement assures that the highly viscous spores do not touch. Should a young spore come into contact with another before their outer shells harden, they fuse and development is arrested. The spores become pigmented at maturity arid are released in sets of paired op-

Figure 52. Two spored basidium. Comparatively few mushrooms have two spored basidia; most are four spored.
Figure 53. Scanning electron micrograph showing f igure 54. A band of Cheilocystidia on edge of gill cross-section of gilL
Mycelium Texture


The method of spore ejection has been a subject of much study and yet still remains largely a mystery. At the junction between the spore and the basidium's sterigma, an oily gas bubble forms and inflates.This bubble swells to capacity and explodes, ejecting spores with a force that has been calculated to represent more than 6 atmospheres of pressure! After e'iculat:.on. the basidium collapses, making way for neigh boring basii ;a, unti1 now dormant, to enlarge. Successions of basidia mature, in ever increas ing quantity, until peaking at the time of mushroom maturity. The well organized manner by which populations of basH'a emerge from the plane of the gill optimizes the efficiency of spore dispersal. After peak spore production, spores cover the gill face several layers deep, hiding the very cells from which they arose With aStropharia, th ; stage would correspond to a mushroom whose gills had become dark purple brown and whose cap had flattened. Spore release at this stage actually declines as the battery of basidia has been largely exhausted and/or because the bas''!ia are rendered dysfunctional by the sea of overlying spores.

Steri e or non-spore-producing cells that adorn the gills are called cystidia. Cystidia on the edge of the gills are called cheilocystidia, while cystidia on the interior surface are called pleurocystidia. (See Figures 54,55 and 56). The cystidia appear to heip the basidia in their devel opment. The extensive surface areas of the cheilocystidia cause the humidity between the gills to rise, thus preserving the hospitable moist microclimate necessary for spore maturity. Some pleurocystidia can project well beyond the surface plane of bas:' ■: a and in doing, keep the gills from contacting one another Should the gills touch, spore dispersal is greatly hampered. As the

Figure 57. Mycelium of Pleurotus cystidiosus and allies, species possessing both sexual and asexual life cycles. Black droplet structures contain hundreds of spores

mushrooms mature, cystidia swell with metabolic waste products. Often times an oily droplet forms at their tip1;.The constant evaporation from these large reserviors of metabolites is an effective way of purging waste by-products and elevating humidity. Some species having pleurocystidia often have a high number of gills permm. of radial arc. In otherwords: more gills; more spores. The survival of the species is better assured.

Once spores have been discharged, the life cycle has come full circle. Mature mushrooms become a feasting site for small mammals (rodents such as squirrels, m;:e, etc. ), large mammals (deer, elk, bears, humans), insects, gastropods (snails), bacteria, and other fungi. From this onslaught, the mushroom quickly decomposes. In due course, spores not


transmitted into the air are carried to new ecological niches via these predators.

Many mushrooms have alternative, asexual life cycles .Asexual spores are produced much in the same manner as mold spores—on micro scopic, tree- like structures called conidiophores. Or, spores can form imbedded within the mycelial network. Oidia, chlamydospores, and coremia are some examples of asexual reproduction. In culture, these forms appear as "contaminants," confusing many cultivators An excellent example is the Abalone Mushroom, Pleurotus cystidiosusmd allies. (See Figure 57). The advantage of asexual reproduction is that it is not as biologically taxing as mushroom formation. Asexual reproduction disperses spores under a broader range of conditions than the rather stringent parameters required for mushroom formation In essence, asexual expressions represent short-cuts in the mushroom life cycle.

A cultivator's role is to assist the mycelium as it progresses through the life cycle by favorably controlling a multitude of variables. The cultivator seeks maximum mushroom production; the mycelium's goal is the release of the maximum number of spores through the formation of mushrooms. Both join in a biological partnership. But first, a strain from the wild must be captured. To do so, the cultivator must become skilled at sterile technique. And to be successful at sterile technique requires a basic understanding of theVectors of Contamination.

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