5.5.26    Ilyonectria radicicola fungus germinates hardy orchid seeds

I have been busy over the last 2 years or so working on (amongst other things!) a project to isolate a new orchid fungus from natural soil. My findings so far have just been published in the Journal of the Hardy Orchid Society, Vol. 23, No. 2 (121), Spring 2026, pp54-61.

A fuller account can be found in that article. The gist of it is that I incubated small samples of natural soil from an orchid area in a West Sussex garden with seeds of the Early purple orchid (Orchis mascula). After 4 months there was germination into a small cluster of protocorms. These were seen to be associated with a fungal mycelium.

I was able to transfer the protocorms into a medium I devised called Sterilised Artificial Soil (SAS). This consists of shredded cardboard, composted bark, wildflower grass seed and some of the natural soil, all being mixed together and sterilised by autoclaving. The fungus grows well in this medium. Protocorms transferred into fresh SAS grow and give rise to further germination when more orchid seed is added in.

To date, I have had four UK hardy orchid species germinate with the fungus: Early purple (Orchis mascula), Greater butterfly (Platanthera chlorantha), Lesser butterfly (Platanthera bifolia), and Twayblade (Neottia ovata).

I also grew the fungus out of a protocorm and across a gap into an agar-oats nutrient medium in a Petri dish. This gave a pure culture which was sent to the laboratories of CABI (Commonwealth Agricultural Bureaux International) for identification by DNA analysis.

They found it to be in the Ilyonectria radicicola species complex. They are soil-borne pathogens causing root rots, rusty root, and black foot disease in commercially important plants such as grapevines, ginseng, Narcissus and others. There is a reference to an Ilyonectria causing germination in a tropical epiphytic orchid but I haven’t found any mention of it in relation to hardy terrestrial orchids. It is in the Ascomycota division of fungi which is interesting because most recognised orchid fungi such as Ceratobasidium and Tulasnella are in the Basidiomycota.

The isolated fungus has not germinated orchid seeds when simply grown on agar-oats medium. It seems to need to grow in the environment of the SAS medium to be able to cause germination. This contains a small amount of the native soil, which may supply an unknown factor that is otherwise missing. I like to think of this as the “Secret Sauce” factor.

Work continues!

Anthony.heys@sky.com