Agar and Mycology – What is it for?

Introduction

agar without nutrientsAgar is used a lot in mycology (growing mushrooms) and has multiple uses. In case you don’t know, agar (some times sold as ‘agar-agar’)is a jelly-like substance made from algae (seaweed) that is commonly in vegetarian foods, amongst other things. It can also be used as a thickener or stabilizer in sweet or savoury food. So you might wonder what it has to do with mycology!

Well, the simple answer is that it’s actually indispensible once you get serious about growing mushrooms. To explain why, let’s look at how people generally start off in mycology.

How we get started

We’re always told we shouldn’t generalise, yet it’s the best way to explain things to most people. So, and in general and ignoring the reasons why, people usually start off growing mushrooms by buying a simple ‘grow your own’ kit with everything included or, in the case of people growing things like cubensis mushrooms, by getting their hands on an ‘all in one’ grow bag along with a syringe of liquid culture or spores to inoculate it with. If you’re lucky, all wil go as planned and you’ll have a lovely crop of mushrooms to harvest. So you’ll do it again.

Eventually, because it always will, something goes wrong and you end up with a green mould farm, a bad smell and an absence of mushrooms. At that point you’ll go online to see what might have caused the problem and will come across people on social media who’ll tell you it must be the fault of your suppliers who sold you contaminated products. They’re usually completely wrong. It is very rare for any business that supplies growing media for mushrooms to supply defective product. It’s their job not to – it would be like a bicycle manufacturer supplying you with a bike that has square wheels – and wouldn’t survive more than a few weeks if they did.

Reality knocks on the door

You might also come across people who’ll tell you that you need to look carefully at your sterile working techniques, talk about still-air boxes and flow hoods and incubation conditions. They might also talk about agar testing for mycology. Listen to these people.

How is agar used in mycology?

Firstly, in terms of preparation, agar is mixed with a nutrient such as malt extract, yeast extract, dextrose etc, added to distilled water, then sterilised and poured into petri dishes to cool and set. Once the agar cools, it sets into a yellow/brownish jelly. Agar can also be made without added nutrients to allow rescue of mycelium where heavy contamination is expected (starving potential contaminants can help). Some people add food colourings to agar to make it look prettier but that’s just for barbie fans, so let’s move on.

Once the agar dishes are prepared and ready to go, small samples of liquid culture or spore solutions can be dripped into the dish, which is then sealed and left to incubate. Very soon, stuff starts to grow on the agar. Hopefully, you’ll see white mycelium start to colonise the agar, and if you see anything else or other colours, you’ll start to recognise the various forms of contamination that plague mushroom growers. If you see nice healthy mycelium, you can happily use your liquid culture or spore syringe.

Most regular growers use agar in mycology to test liquid cultures and spore syringes for contamination. If you look at a syringe of liquid it’s almost impossible to tell if it is safe to use, or if something has crossed over and contaminated the contents. Spore syringes are notorious for carrying contamination, and not simply because the supplier is incompetent. When spores are scraped from a print to make your syringe it’s impossible to be 100% sure that there were no competing spores or bacteria on the print. Most spore syringes are sold ‘clean’, but a fair percentage are not. That’s why growers are always told not to use spore syringes unless really necessary, or unless agar tested first.

Other uses of agar in mycology

Contamination on agar

What you don’t want to see!

If you know someone with OCD cleanliness tendencies you can have a little fun with them. Gift them half a dozen agar dishes, telling them to leave them open for 10 minutes, one in each room in their house, then put the lid on and leave them in a warm shaded place for a week or two. What grows will be enough to give them a purple fit.

Joking aside, testing for purity is the first reason to use agar but it’s far from being the only one. It’s just the first step of many. To give you an idea, here are some of the things you can use agar for:

  • Create guaranteed clean liquid cultures
  • Guarantee a spore syringe is clean before use
  • Clone and refine clean mycelium grown during the above tests to enhance its quality
  • Rescue and clone clean mycelium from any tests that showed contamination
  • Harvest and clean up genetic material from mushrooms you’ve picked from outside
  • Use spore swabs to create mycelium from low-spore species
  • Clone mycelium from fresh (purchased/picked/grown) mushrooms
  • Use colonised agar to start a fresh liquid culture
  • Use colonised agar to inoculate sterilised rye and create grain spawn

Agar and Mycology are a perfect combination – agar allows you to test for contamination, allows you to clone, grow and develop clean, high quality mycelium and can be used to create clean grain spawn at the same time. However, remember that you are no less liable to create your own contamination when using agar than in any other aspect of mycology, so strict adherence to sterile working practices and incubation environments are especially important – there’s no value in testing on agar if you breathe all over it or allow competing spores or bacteria to join the party!