[compost_tea] Re: Greenhouse

From: Tom Jaszewski <tom_at_livesoil.com>
Date: Thu, 30 Dec 2004 01:55:18 -0000

1. Orchid mycorrhizas
Some types of orchid are non-photosynthetic; others only produce
chlorophyll when they have grown past the seedling stage. In all
cases, the plant depends on sugars derived from a fungal partner for
at least part of its life. The minute orchid seeds, with negligible
nutrient reserves, will not germinate unless a fungus infects them,
although the seeds can germinate aseptically if supplied with
the 'fungal sugar' trehalose.

These mycorrhizas are unusual because, in effect, the plant
parasitises the fungus that invades it. The fungi in these
associations resemble the common plant pathogen Rhizoctonia solani,
but recent taxonomic studies have assigned them to several related
genera. They are mainly saprotrophic - they grow by degrading organic
matter in soil - but they might obtain trace elements or some other
factor from the plant.

An interesting variation on this theme is shown by some orchids and
other non-photosynthetic plants (Monotropa species) that have wood-
rotting species of Armillaria as their mycorrhizal symbionts. In some
of these cases the fungus can even be a pathogen of tree roots, so
that the non-photosynthetic plant gains its nutrients by indirect
parasitism of a living tree (see Armillaria).







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Received on Thu Dec 30 2004 - 00:36:20 EST

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