Potato Dextrose Agar (PDA)

In the early stages of working with mushrooms, the environment needs to be as sterile as possible. In the early stages of growth, mushrooms cannot compete with the growth of molds and bacteria and will be over run.

Preparing your Potato Dextrose Agar (PDA)

For every 1 Liter of Agar Final Mixed Solution you will need the following.

  • 20 grams Bacteriological Agar
  • 200g Potatoe infusion
  • 4 g of Yeast Extract
  • 20 g Dextrose
  • 1 Liter of Distilled Water
  • Autoclave or Pressure Vessel

Method:

  1. Place your pre cleaned flask on a kitchen scale. Make sure your scale now reads Zero. Add your dry ingredients first.
  2. Now add potatoe infusion until the scale reads 250 grams.
  3. Pick up the flask and swirl the solution until no dry matter can be seen and most of the agar has been dissolved.
  4. Return the flask to your scale and add water until your reach 500 grams. Again swirl the solution.
  5. Return the flask and add water until you read 1000 grams. Again swirl the solution.
  6. Cut a piece of tin foil – 300 mm by 80 mm. Roll up a piece of kitchen towel into a tight roll.Now, half way sticking over the mouth of the Erlenmeyer flask, wrap your tin foil in a tube around the glass. Place the rolled up kitchen towel in the tube and fold over the mouth of the flask to hold the paper. (This acts as a filter when autoclaving your solution. As pressure drops in your pressure vessel, the flask will balance air pressure and suck in air, for this reason we need a filter.)
  7. Pressures sterilize the Agar solution for 45 minutes.
  8. Open the pressure vessel, once cooled, in front of a flow hood or in a cleaned environment (glove-box).
  9. Pour your agar into petri dishes (90mm) or small glass jars for use, do this rhythmically and do not linger. From 1 liter of Agar you can make 35 – 40 dishes.
  10. After pouring and cooling your agar dishes, keep them in a big zip lock bag, to ensure they do not contaminate. You can keep these in the fridge for 28 days.

Prepare potato infusion: 

Wash two medium sized potatos (200g) and cut them into 2.5cm cubes and place in a clean pot and add 1.25 liters of CLEAN water. Bring to boil and keep the simmering temperature for 10 – 15 minutes. At this time remove the pot from the stove and allow to cool down for 5 minutes. Strain the water away from the potatos (use a fine sieve or french press) and use this water to prepare your potato infusion.

(PDA) Agar is made and then poured into petri dishes and then sterilized. The petri dishes are then moved into a clean room that contains a glove box. Cultures are taken from the mushroom and placed onto the agar in the petri dish.

Sampling a mushroom: 

With clean fingers, in a clean space or glove box, split the mushroom down the middle. You will notice clean white mycelium on the inside of the mushroom that has never been exposed to air or the environment. Using a cleaned scalpel cut a piece of this mycelium and place in your readied container.

When significant growth has occurred on the agar, the agar is cut and placed in either grain to make grain spawn, nutrified liquid to make liquid culture or expanded onto more petri dishes.

Cloning Mushroom Tissue

 

Liquid culture and grain spawn can either be expanded or used to inoculate a substrate such as coffee or sawdust.

The substrate is then incubated usually in the dark under controlled climatic conditions. This can be done in a home made incubator or a room that has climate control.

Once the substrate has been fully colonised and consolidated it is moved into fruiting conditions. The fruiting conditions make the mushroom mycelium think it is under stress and dying so it sends its reproductive organs out to reproduce we call this it’s called fruit.

 

 


 

Making Potato Dextrose Agar Petri Dishes for Mushroom Cultivation

Learn to grow mushrooms! Being able to do agar work is an essential skill for the cultivator. It allows you to propagate cultures, maintain a culture library and store cultures for the long term.

 

 

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