Many studies indicate that the germination of orchids needs assistance from mycorrhiza. However, in-vitro germination is very common for orchids (especially epiphytic orchids) cultivation. I wonder whether orchids need a fungal partner to germinate or to grow soon after germination?
Yes if you do aseptic culture then the growth is much slower in comparison media with some fungal associates....
The dependence on fungi for germination is varibale in different plant species: for instance, epiphytic orchids can germinate and develop without fungi (but in the presence of exogenous C). In general, the presence of the fungus is required in the first stages post-germination because of the very few reserves stored in the orchid seeds (which are very small).
To some orchids species, mycorriza association is more determinant on acclimatization and initial growth phase than to germination phase, meanly in assymbiotic conditions.
Mycorhiza symbiosis is effective to induce germination of terrestrial orchids and some epiphytic orchids. I have experience to inoculate the fungus before and after seed germination of terrestrial and epiphytic orchids. The result showed that the fungus effectively induced germination of terrestrial orchids, but not epiphytic orchids. Instead of mycorhiza, the use of tomato extract was also effective to promote seed germination of orchids. The growth rate of the orchid protocorms become faster when 100 mg/L tomato extract was added into the culture medium. It might be due to the content of lycopene and vitamins,etc in tomato extract. But, longer treatment with tomate extract was not good, it wiill inhibit the orchid growth, It means tomato extract can only be used as trigger for germination and promotion of initial growth phase. After 3 weeks we transferred the protocorms onto tomato extract-free medium, so the orchids grow faster than that of the control (non treated ones)..
Most of my experience has been with native Australian terrestrial species, these orchids can be germinated aseptically in vitro in a complete medium, but the process is generally significantly longer that symbiotic germination. In nature it is unlikely that this ever occurs, orchid seed contains very little endosperm and germinating seed and seedlings are dependent on their mycorrhiza for C nutrition.
Once germinated aseptically the plants then need to have the symbiosis established prior to potting out or need to be planted into an inoculated medium. Failure to do so results in rapid and complete loss of seedlings or plants.
Orchid mycorrhizas are different from other types of mycorrhizas in the nature of the nutrient exchange. After establishment of a mycorrhiza, organic carbon and minerals are passed from the fungus to the seed. Because asymbiotic germination requires sugars, amino acids and vitamins, it is assumed that these are also obtained from the fungus. The fungus continues to supply the protocorm with all its organic energy until such times as the plant starts to photosynthesise. Even then, it appears that the fungus does not gain significant supplies of carbon from the photosynthetic partner.
Orchid symbionts can include fungi from Rhizoctonia sensu stricto that are pathogens on other plants.
Thank you for all the helpful answers! I and my colleagues try to germinate several Cypripedium species for rehabilitation. We only successfully germinate C. debile once, but never did for other 3 species. I agree most epiphytic orchids are easy to germinate in vitro. After reading your answers, It seems we have to find the specific mycorrhiza to help them germinate then.
Hola Rebecca:
Look this work: Re-establishment of the lady’s slipper orchid
(Cypripedium calceolus L.) in Britain
file:///D:/Marcela%20S%C3%A1nchez/Downloads/Journal%252BNo%252B4%20(1).pdf
This group of mycorrhiza have a unique role in the life cycle of Orchidaceae family plants. In species without chlorophyll, plant during the whole term of life, to meet the needs of carbon is related to its fungal partner.
Its Obligatory symbiotic relationships with orchids in both early and later stages of the development.
We believe that to some species fungal presence is determinant meanly in the acclimatization phase, but not in the germination phase. However fungal presence in the germination phase accelerates this process for many species, but it is not determinant to obtain high germination percentage in the Brazilian native orchids.
Hello Rebecca !! Maybe I'm a little late with the answer, but not quice quit because I found it very interesting question why I have voted as such, especially for those who are starting in this field. Undoubtedly I agree with different opinions indicating that the required symbiotic association after germination, otherwise no seed cultivation could be carried out in the laboratory. It would be good that you comment on the conclusion to the answers after they have given specialists, which would be a great contribution for those who have little experience in the area arrived. regards
Hi Rodolfo, Thank you for the suggestion. As many specialists indicated in this thread, we did find it seems case by case. For example, we successively germinated both the Cyprepedium debile and C. macranthum. The former could be cultivated in vitro whereas the latter could not. We guess it probably involves some symbiotic fungal.
Rebecca, it's interesting that they found those results! I wish that when they publish the results make me a copy. Some time ago I put a question, which leave the link at the end of this message, which Zygopetalum maxilare develops naturally only in Alsophila setosa. We are beginning work to try to grow this species under other conditions, but we always had the doubt if the need was host germination or growth. In vitro culture it grows, so we understand that the host is essential for growth. Our interest in advancing this study is that both species are in decline. regards
(https://www.researchgate.net/post/Why_does_the_Zygopetalum_maxilare_develop_on_Alsophila_setosa_and_not_on_the_other_plants)
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