Since we began propagating orchids in vitro, we noticed that some generas (e.g. Bulbophyllum) suddenly die after a couple of months in their flasks. The reason for this sudden death was the absence of gas exchange. Seedling produce e.g. ethylene while they are growing which sometimes will kill them if we do not remove it. To solve this problem we have to give our flasks the chance to exchange air. In the past we drilled a hole in the lid of the flasks and put a cotton plug in it to keep contaminations (fungi, bacteria, ...) out. The disadvantages with using cotton wool is possible contamination risk.
dying seedlings (without venting)
On the internet we found a supplier (Tissue Quick Plant Laboratories TQPL) which sells adhesive filter discs for venting flasks. TQPL offers two different types of filter discs: Adhesive Microfiltration Discs (AMDs) and Flasking Patches (FPs).
AMDs and FPs consists of a filter discs with an adhesive ring and can be applied easily.
How do filter discs work ?
The basic function of filter discs is the same as in HEPA (High Efficiency Particulates Air) filters. The filter discs has a high number of very small holes which are big enough to let the air pass through but they are small enough to hold contaminations (fungi, bacteria, ...) off.
What are the differences between AMDs and FPs ?
The differences are found in the way they are produced. FPs are produced by streching a standard PTFE (polytetrafluoroethylene) membranes to reach the desired thickness and this allows the formation of a range of hole sizes (all of which are small enough to stop contamination) according to the degree of stretch. AMDs are made of microporous PTFE which does not rely on this stretching process but starts with granules of PTFE all of the same size and is constructed from these resulting in even sized holes being formed. For more detailed informations please visit the website of Tissue Quick Plant Laboratories TQPL.
How to use filter discs
Drill a hole of about 1 mm in the lid of your flask and debur it carefully.
Peel off the AMD or FP from the backing sheet (similar to self seal labels) and apply over the hole.
Dispense the media into your culture vessels and screw the lids loosely on the flasks. Donīt screw down the lid too strongly because the preasure increases in the flasks while you are sterilizing it and that can blow off the filter disc. After screwing down the lid loosely, cover the flask with aluminium foil and sterilize it for 30 minutes and 150 ºC in your oven. Let the flasks cool down in the closed baking oven.
After cooling down the flasks screw down the lids (donīt remove the aluminium foil) and store them in your growing rack till you need them. The picture below shows a Cynorchis growing in a vented flask.
