As mycelium grows out on a nutrient agar, can display a remarkable diversity of forms. Some mycelia are fairly uniform in appearance; others can be polymorphous at first and then suddenly de-velop into a homogeneous looking mycelia. This is the nature of mushroom constantly
and evolve.
a mycelium grows from a single inoculation site and several divergent Types appear, iT is
32/The Mushroom Cultivator
Figure 33 Bacteria growing from con- Figure 34
taminated mushroom mycelium. Note divergent ropey strands.
Figure 35 Intermediate linear type Figure 36 Rhizomorphic mycelia with Note longitudinally radial fine mentose (cottony) sector (of
strands mycelium).
Sterile Technique and Agar Culture/33
to be sectoring. A sector is defined solely in contrast to the surrounding, predominant There are two major classes of mycelial sectors: rhizomorphic and tomentose (cottony). Also, an intermediate type of mycelium occurs which grows linearly (longitudinally radial) hut does not have twisted strands of interwoven hyphae characterize the rhizomorphic kind.
Rhizomorphic mycelium is more apt to produce primordia. Linear mycelium can also produce abundant primordia but this usually occurs soon after it forms rhizomorphs. Keep in mind, however, that characteristics of fruiting mycelium are often species specific and may not conform precisely to the categories outlined here.
a dish That is largely covered with a cottony mycelia, a fan of strandy myceiia would be called a rhizomorphic sector, and vice versa. Sectors are common in mushroom culture and little is known as to their cause or function, it is clear that genetics, nutrition and age of the mycelium play important
According to the growth of fluffy sectors is encouraged by broken and exploded which increase the availability of starch in the spawn media. Working with
Stoller noted that although mycelial growth is faster at high pH levels (7.5) than at slightly acid pH levels (6.5), sectoring is more frequent. He found that sectors on grain could be
37 Psilocybe cubensis mycelia with cottony and rhizomorphic sectors. Note that primordia form abundantly on rhizomorphic mycelium but not on the cottony type.
Mushroom Cultivator
Figure 38 Hyphal aggregates of Agaricus bitorquis forming on malt agar media.
Figure 39 Primordia of cubensis forming on malt agar media.
Technique and Agar Culture/35
duced by avoiding exploded grains (a consequence of excessive water) and buffering the pH to 6.5 using a combination of chalk (precipitated calcium carbonate) and gypsum (calcium
Commercial cultivators have long noted that the slower growing cottony mycelium is inferior to the growing rhizomorphic mycelium. There is an apparent between cot-mycelia on agar and the later occurrence of a dense mat-like growth of mycelia on the casing which rarely produces mushrooms. Furthermore, primordia frequently form along gen-eratively oriented rhizomorphs but rarely on disposed cottony mycelia. It is of to mention that, under a microscope, the hyphae of a rhizomorphic mycelial network are larger and branch less frequently than those of the network.
Rhizomorphic mycelia run faster, form more primordia and in the final analysis yield more mushrooms than mycelia. One example of this is illustrated in Fig. 37. A single wedge of mycelium was transferred to a petri dish and two mycelial types grew from it. The stringy sector formed abundant primordia while the cottony sector did not, an event common in agar culture.
When a mycelium grows old it is said to be senescing. Senescent mycelium, like any aged plant or animal, is far less vigorous and fertile than counterpart. In general, a change from rhizo-morphic to cottony looking mycelium should be a warning that strain degeneration has begun.
If first a is predominantly rhizomorphic, and then it begins to sector, there are several measures that can be to promote rhizomorphism and prevent the strain's degeneration.
Propagate only rhizomorphic sectors and avoid cottony ones.
2. Alter the media regularly using the formulas described herein. Growing a strain on the same agar formula is not recommended because the nutritional composition of the medium exerts an selective influence on the ability of the mushroom mycelium To produce digestive enzymes. By varying the media, the strain's enzyme system remains based and the mycelium is suited for survival. Species vary greatly in their preferences. Unless specific data is available, trial and error is the only recourse.
3. Only grow out the amount of needed for spawn production and return the strain to storage when not in use. Do not expect mycelium that has been grown over several years at optimum temperatures to resemble the primary culture from which it came. After so many cell and continual transfers, a sub-strain is likely to have been selected out, one that may distantly resemble the original in both vitality, mycelial appearance and
potential.
4.If efforts to preserve a vital strain fail, re-isolate new substrains from multispore germina-tions.
5.Another alternative is to continuously experiment with the creation of hybrid strains that are from the mating of dikaryotic mycelia of Two genetically parents.
(experiments with Agaricus have shown, however, that most hybrids yield than both or one of the contributing strains. A minority of the hybrids resulted in more
strains.)
36/The Mushroom Cultivator
Home cultivators can selectively develop mushroom strains by rating mycelia according to sev-eral characteristics. These characteristics are:
growing vegetative 2. Purity of the of cottony sectors.
3. Cleanliness of the of competitor organisms (bacteria, molds and mites).
4. Response time to primodia formation conditions.
5. Number of primordia formed.
6. of primordia formed that grow to maturity.
7. Size, shape and/or color of fruitbodies.
8. Total yield.
9. Disease resistance.
tolerance/sensitivity.
Temperature limits.
12. Ease of harvesting.
Using these characteristics, mushroom breeders can qualitatively judge strains and select ones over a period of time according to how well they conform to a grower's preferences.
Figure 40 stand of
cubensis on malt agar media.
Technique and Agar Culture/37