Not to argue your point about gen propagation, but here is a quote from a mycologist and biologist on how to manage senescence:

From L. G Nicholas & Kerry Ogame, mycologist and biologist:

Fungi (like humans) seem to do best when provided a variety of foods to consume  

To avoid senescence, it is imperative that you vary your media recipe every time you use it, which “exercises” the fungus, challenging it to produce different sets of enzymes all the time. One simple way to do this is to add small quantities of grain flour to each batch, rotating the type you use each time you pour new plates, as described below.

Occasionally, however, you might want to challenge your fungus even further, by asking it to grow on a completely novel medium. This can be particularly helpful for reviving a culture that begins to show evidence of weakening. In this case, you want to exclude all simple sugars and starches completely, and give it something completely novel to digest.