What is purpose of propagating mycelium in a potato dextrose agar medium?

Asked February 2, 2015, 1:34 PM EST

Why start mycelium (for Shiitake mushrooms) in a potato dextrose agar medium, then introducing it into a secondary substrate (e.g. Wheat), when mycelium can be propagated in sterilized grains such as wheat to begin with? This extra step simply appears to be unnecessary to me and the belief it would increase the chances of contamination. Reference: https://www.youtube.com/watch?v=QIZQ39wYkI0

Peoria County Illinois

1 Response

If you are referring to establishing a new mycellial clone from a fruiting body (sporocarp), avoidance of contamination is essential. PDA is an encrich medium consisting primarily of glucose (dextrose). A small inner (sterile) piece of the mushroom, transferred to PDA initiates growth more rapidly than it would on a more complex substrate like grain. Once it begins to grow on the PDA it can be easily observed for contamination, which might not be so obvious on sterile grain. Furthermore, lack of contamination can be assured by several (3) subcultures on PDA before transfer to grain, whereas multiple subcultures onto grain would take longer.