Some mushroom strains have been maintained by man for over a century. There are a few methods to do this, of which Mycelia uses three. You will find a short overview below.
Proper strain maintenance is very complicated, but it is man's best protection against a number of problems. What are these problems?
a. Contamination. If during production, a contamination problem pops up down the chain which occurs only with all descendants of one line, then the line is flawed and must be eliminated. This does not happen often, as these problems usually manifest themselves at the earliest stages of multiplication and can be confined at that point without losing the whole strain.
b. Degeneration. Strain degeneration is probably the spawn producer's worst nightmare: due to constant replication of the same strain, small DNA defects - mutations - start occuring. Over a longer period of time, sudden degeneration may occur in a strain and cause problems like deformations, irregular or no fruiting, etc. This is the reason that subculture method can only be used for a certain amount of time. After a while, the strain must be abandoned, the original strain must be taken from the deep-freezer and from that point, subculture method can start off again.
Subculture method is used by all professional spawn producers worldwide. It is the term used for multiplication of the mother cultures through means of duplication, often creating parallel descendants of the same mother cultures which are then called 'lines'. These lines are then further multiplied into mother spawn, spawn and finally substrate. It is in fact a form of cloning (sensu lato).
Mycelium can be kept in deep frozen condition for extended periods of time if it is frozen at extremely low temperatures. It is unknown to science for how long mycelium can survive in such frozen conditions, but there have been experiments over periods extending 15 years which produced still active mycelium, even after cycles of freezing and defreezing.
Freezing requires -75°C to -80°C and can be done with liquid nitrogen or with electric cooling systems. Spawn producers that do not use this method need to buy back their original strains once in a while in order to avoid degeneration.
3. Strain refreshment
Scientific research and experience has shown that it is wise to duplicate the mycelium every couple of years in order to keep strains from degenerating. One will simply gather a small part of a fruit body and grow mycelium from this. This will then become the new parental strain from which the fresh mother cultures will be derived.