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I recently started growing some Geotrichum Candidum (GC) on Sabouraud dextrose agar (SDA) beds. The SDA was poured into sterilized petri dishes. After setting the plates in a cooler (20 C) for a day, I then inoculated the plates with a tiny smidge of GC. The GC is growing happily in that environment.

However, today on day 3, I noticed a crack across the SDA like shown in the picture below.

What does this mean? Did I prepare the plate wrong? Or is my GC just a bit naughty and somehow burrowing into the SDA?

Please note I am not a trained biologist, I've learned the skills I require for my activity from online resources and advice.

a crack in sabouraud

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    $\begingroup$ It could just be the agar drying out. $\endgroup$
    – canadianer
    Commented Jul 21, 2021 at 0:20
  • $\begingroup$ My initial thought. The cooler is at 80 % relative humidity though. Isn't that enough? $\endgroup$
    – neydroydrec
    Commented Jul 21, 2021 at 0:45
  • $\begingroup$ I suppose evaporation can occur at any relative humidity less than 100%. Is the agar shrinking in terms of thickness and/or peeling away from the side of the plate? These are also signs of desiccation. $\endgroup$
    – canadianer
    Commented Jul 21, 2021 at 0:59
  • $\begingroup$ I see no signs of desiccation on the surface nor on the edges of the agar. $\endgroup$
    – neydroydrec
    Commented Jul 21, 2021 at 1:04
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    $\begingroup$ @neydroydrec If that turns out to solve your problem, can you please add it as an answer to your own question? Then it will help the next person with a mysterious crack in their agar. $\endgroup$
    – jakebeal
    Commented Jul 22, 2021 at 1:25

1 Answer 1

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I cannot be entirely sure about the cause as I have not been able to reproduce this situation subsequently, but based on the comparison of what I did before and do now, it seems the cause was the wrong dosage of agar per water, i.e. an excess of agar. Hoping this may help others.

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