07 03/07/2017

Conservation scholar: interaction between orchids and fungi

  • At The Zoo
  • Plants and gardens

Conservation Scholar, Oliver Hughes, has spent five years working on orchids for his MPhil and PhD. He tells us more about the fascinating interaction between orchids and fungi and how he has been working on improving the propagation of different orchid species.

Often colourful and exotic, orchids are well-known around the world and many species of them are sold as ornamental plants. However, their survival in the wild relies on a very specific interaction with fungi. On the contrary to most plants, orchid seeds do not contain any cotyledon or carbohydrate reserves to germinate. In order to germinate, the seed needs to come into contact with a fungus that will then penetrate into the seed coat infecting the cells of the embryo. This natural propagation method is defined as symbiotic.

Oliver tells us more, below:

“It starts digesting some of the fungal coils within the cells, called pelotons, and the plant then uses that energy to grow and germinate until it develops to the point it makes a green shoot. At that point, until they make a green shoot, it’s fully parasitic on the actual fungus and only when the plant produces a green leaf, does it starts producing sugar which will then feed back to the fungus. That’s when it becomes a mutual symbiosis where neither one loses out. 

Orchid
Anacamptis morio, green-winger orchid seedlings on symbiotic media with B1 fungus, two months from sowing. Seedlings have developed green leaves and in some cases roots.

"Recreating this process to propagate orchids is a difficult task because different orchid species have symbiotic relationships with different fungi and that’s why commercial propagation techniques usually rely on asymbiotic methods. Working to develop these methods further could allow for the production of larger numbers of more robust orchid plants that are associating with appropriate mycorrhizal fungi. These plants could then be passed to relevant nature conservancy agencies for reintroduction into suitable habitats, helping not only to restore rare plant species but also mycorrhizal fungi, and in doing so, ensuring that future orchid populations are self-sustaining.”

For his PhD, Oliver decided to test both asymbiotic and symbiotic methods on two categories of orchids: terrestrial species, mostly found in the UK and Eurasia; and pleurothallid orchids, a sub-tribe of mostly epiphytic species distributed along Central and South America and the Caribbean.

Oliver continues:

“In the case of Eurasian terrestrial orchids and pleurothallid orchids, we tried to isolate fungi from the roots of the orchids themselves. Usually, the best way to get the most effective fungi (the ones actually involved in germinating the seeds) is to find a protocorm. This mass of cells able to differentiate in different parts of the plants is responsible for the formation of shoots and roots and can be only few millimetres long making it difficult to spot. A fungus isolated from the orchid at that stage is likely to be one involved in the germination and growth of the plant making this stage of development quite crucial for my research. 

Orchid anlax
Protocorm of Anacamptis laxiflora, the Jersey or lax-flowered orchid sown on symbiotic media with B1 fungus at three months from sowing. The protocorm is showing a photosynthetic leaf shoot and rhizoids.

“It’s a matter of trying lots of different fungi and picking out those ones that are good fungi and will actually develop full plantlets that you can then plant out and utilise as a plant to reintroduce into the wild. In order to compare both methods, I trialled a lot of different fungi isolated from the orchids present in Chester Zoo’s collection and also trialled different asymbiotic media on seeds collected in the zoo.

“Overall I think I tried to pollinate over a 100 or 200 species altogether but we only got maybe 10 or 20 species that were actually successfully pollinated. The experiments were taking place over long periods of time from sowing the seeds until germination, six to 12 weeks later, and then measuring the orchids’ growth a month, three months, six months and sometimes years later. 

“Often I’ll set a lot of experiments at once. Then I could measure them at specific time points throughout the following six months essentially. One set of experiments was conducted on Orchis, a genus of European and Mediterranean distributed terrestrial orchids and consisted of 10 different orchid species with 14 different treatments each having 15 petri dishes replicates to allow for statistical analyses. Another set of experiments was also conducted on 15 species of Pleurothallid orchids.

Masdevallia veitchii orchid
Masdevallia veitchii. Credit: Steve Manning.

“My findings reveal that both methods are effective on terrestrial orchids. However, identifying and matching the appropriate fungus to each orchid has proven to be more effective, resulting in higher germination rate, quicker development rate and also higher survival when planted into a greenhouse environment. 

“We did one experiment with the Anacamptis (Orchis) laxiflora. We planted asymbiotic seedlings and all of them died, however, about 90% of the symbiotic seedlings survived in comparison and they were also a lot bigger and more able to survive in conditions outside. For the Pleurothallid orchids, none of the strains of fungi tested developed full plantlets. However, symbiotic germination using two fungal strains isolated from the orchids Masdevallia menatoi and Dracula felix produced higher germination rates (40 to 60%) than the asymbiotic method (10 to 20%).

“This is not unusual as many fungi can induce germination in orchids. There can often be a narrowing in the number of fungi which can induce further plant development so I would presume in this case we didn't find the magic one or few that would induce plantlet formation.

Protocorms orchid
Early stage photosynthetic protocorms of Masdevallia menatoi, Menato's Masdevallia on asymbiotic media at 2 months from sowing. Protocorms are starting to display rhizoids

“Despite lots of trials and errors and a few failures, the research project also had significant highlights. A few rare species were propagated for the North Wales Wildlife Trust and also for Natural England. We propagated frog orchids (Coeloglossum viride) successfully with both asymbiotic and symbiotic methods and also green-winged orchids (Anacamptis morio) which are not particularly rare but have been exterminated in certain habitats so they are a good species to work with especially in the north of England.

Trisetella hoeijeri CREDIT Steve Manning
Trisetella hoeijeri orchid. Photo credit: Steve Manning

“Looking into the future, the best way to isolate the right fungi for propagation would be to isolate them from orchid protocorms and seedlings where they are growing in the wild. That would allow scientists to get a full range of what these fungi might be. The interaction between the orchid and the fungus is not necessarily a two ways beneficial interaction, if you change the conditions the fungus can often kill the orchids. It’s almost in a state of symbiosis/parasitic relationship depending on the conditions so that’s why you need to get the conditions quite right and specific to what the orchids would have experience in its natural habitat.”

Orchids
Plants of Anacamptis laxiflora, The Jersey or Lax-flowered Orchid sown with B1 fungus in cultivation in a temperate greenhouse at 26 months from sowing (eighth months growing outside of flask).

Oliver's PhD research is run in partnership with Manchester Metropolitan University, to find out more about Oliver's work head over to his lab page here.