Fungi and allelopathic plants

One of the problems faced by many people planting polycultures is the fact that many plants exude compounds that inhibit the germination of competitor plants, of which the most annoying from our perspective is probably juglone (exuded by the roots of, among others, walnuts, which is where my thinking on this post started).

My existing reading suggests that fungi can be pretty good at metabolising a range of toxic substances, and it occurs to me that that there may be some species out there that will break down these substances. Does anyone know anything about this?

Holy grail: an edible mycorrhiza that will break down or protect other plants from juglone, along with the means of inoculation.

Anybody?

Any information on fungi and other allelopathic substances might also be useful to someone. The more I think about these problems from an ecosystem perspective the more I suspect there's a solution somewhere, and fungi seem like a worthwhile area to follow up.

Good thinking - I could user that to as I have a young Juglans regia in my garden that was gifted to me.

Don't know about fungi that might detoxify juglone, but there are bacteria that have been found to be up to the task. I'm thinking that much of the microbial biocontrol for crop protection literature and efforts have focused on bacteria, one reason being the ease with which they can be produced in batch culture as well as formulated for a seed/root application. So one approach, if trying to establish seeds/seedlings of other species near the rhizosphere of black walnut would be to find a rhizosphere-competent bacterium for that plant species that also is known to be able to detoxify juglone. Can't imagine a commercial product having those qualities, but tunneling through some research contacts may yield something to try, especially as it would be unlikely to require regulatory oversight.

Fluorescent Pseudomonad ID'd for degrading juglone: http://amo.colorado.edu/schmidt1988.pdf

(Fluorescent Pseudomonads have a deep history in research on the biocontrol of plant pathogens.)

For a good review on juglone, see: http://jem.forrex.org/index.php/jem/article/viewFile/119/473

(Let me know if links are dead or protected.) It's probable, given the chemical nature of juglone, that walnut tree variants that do not produce juglone might be found, but given the high toxicity of juglone to insects, I suspect it would be deficient in one of its main defenses against insect predation.

Good question. Non mushroom forming mycorrhizal fungi know as asrbuscular mycorrhizal fungi (AM) are known to transport juglone throughout their mycelial networks, helping reduce its concentration.

Peter

That's really interesting. I wonder if mycorrhizal fungi contribute to something that's always been a bit of a puzzle to me. In Gaea's Garden, Toby talks about apple trees being planted near black walnuts in a guild, although many other sources say apples are negatively effected by juglone. Apparently this is related to the mulberry planted in between the apple and the black walnut acting as a buffer - maybe it's related to mycorrhizal fungi that favor mulberry roots that help create that buffer.

Just a speculation.