Biology of orchid seed germination

Orchid seeds are very small (like dust) and do not contain any food reserves which feed the embryo in his first steps of life like other plants do (e.g. apple, beans). Because of this fact, orchids produce a high number of seeds (up to 1 millon in each capsule).

mature Phaius tankervilleae capsule

In nature the embryos swell a little bit but they will not form a seedling unless they are infected by a symbiotic fungus (mycorrhizal fungus) which supplies them with sugar and nutrients. As soon as the symbiosis is established each embryo becomes a little "ball" which is called protocorm. These protocorms turn green after a while and the first leaf and roots appear. From this stage the seedlings can live without the symbiotic fungus because the photosynthesis is active.

Encyclia vespa protocorms	Cyrtopodium punctatum protocorms

We have germinated seeds of Epidendrum radicans which build green protocorms after 2 weeks. Cyrtopodium punctatum protocorm took for the same stage more than 2 months.

Cyrtopodium punctatum protocorms with first leaves	Epidendrum radicans protocorms with first leaves

Symbiotic germination in the pot of the parents

This is a very old technique which was used before in vitro culture was discovered. Here we use the symbiotic fungus which is growing on/in the roots of the adult orchid (which produce the capsule). The seeds are sown very close to the roots and are kept moist to start germination.
The number of seedlings is limited because many protocorms and seedlings get killed by pests and aggressive fungi.

Symbiotic germination (in vitro)

At this technique we have to isolate the symbiotic fungus from a root of the orchid where the capsule was produce. The fungus has to be established on a nutrient-poor media (e.g. oat meal agar). Next we have to sterilize the orchid seeds and saw them on the media which contains the isloated fungus. The seeds will germinate and produce seedlings if the isolated fungus is compatible with the seeds. If not, no germination will take place.
With this methode it is possible to rise much more plants from the same quantity of seeds as we can do with "Symbiotic germination in the pot of the parents".

Asymbiotic germination (in vitro)

To avoid the high effort, which is needed to isolate and test the fungus, we can "simply" ignore the fungus and add all necessary nutrients (which are provided by the fungus) to the media. The only thing we have to do is to cook the media and saw the seeds under sterile conditions on this media. For more details please read asymbiotic seed germination.