An assessment of the fungal specificity of the orchid sub-tribe Pterostylis

Seed Germination Experiment

Almost all orchids are depending on mycorrhizal fungi during their full life. Especially by their germination, the mycorrhizal is needed.  The seeds of the orchids are very small and only got a little stock of nutrients, therefore they require fungus to transport the necessary nutrients from the soil to the seed.

This experiment shows the relation between the orchid Pterostylis and different types of mycorrhizal fungi, which occur in east and west Australia. For this experiment they took seeds from an orchid and put them in a Petri dish with a medium, to avoid the natural variability, they took the seeds only from one orchid. Afterwards they added a specific mycorrhizal fungus to the Petri dish and could see with which fungus the orchid makes a symbiosis. Without a suitable fungus, the seed wouldn’t grow that much, because the orchid couldn’t get the nutrients out of the medium.

The result shows that the growth indices of the fungal treatments were significantly higher than the growth indices from the control. It also shows the variation in growth within the fungal treatments themselves.  Not only closely related species of mykorrhiza can have similar impacts of the germination, also less related clades can be similar. The results confirmed that the orchid Pterostylis can germinate with several mycorrhizal fungus successfully. The seed germination rate form east and west Australian fungus was not significant, so it doesn’t matter from which locality the fungus comes from. There must be other environmental influences which affect the orchid growth rate in this region.

 

 

Molecular Experiment

With the new molecular technique it is possible to produce fragments of DNA. With the agarose gel electrophoresis it is possible to see the lengths of the base pairs in a photo. In the fragments are different intron types and each of the intron type is adapted to only one clade (exception one clade, which contained with three intron types). With this information it can be easier to determine the clade of the fungus without doing a costly DNA sequencing.