Re: [compost_tea] Exudates (was: Re: Brassicas and vam fungi)

From: <soilfoodweb_at_aol.com>
Date: Tue, 2 Nov 2004 10:28:19 EST

Thomas -

It sounds like you have concluded that brassica, in general, and
VAM-requiring plants can be grown together. That is not the conclusion that would be
taken from the papers you pointed out. You have not demonstrated that anyone is
suggesting that brassica and mycorrhizal plants can be GROWN TOGETHER.

Now, it is useful that you point out the one paper that says a certain
cabbage species can be mycorrhizal. Thank you for bringing that paper to the
attention of the group.

Your first abstract said,
"The results suggest that the inhibitory effect of root extracts of non-host
plants (Crucifereae) on spore germination can not be attrributed solely to
presence of volatile substances and extended to other non-host plants."

This does not suggest that non-host plants plants can be companions of host
plants. It clearly says there are other mechanisms involved in the inhibition
of VAM by brassica than just the volatile glucosinolates. As I recall, it is
glycosinolates, not glucosinolates that are the inhibitory compounds. I need
to check if it is glyco, or gluco. It would be different structures depending
on the y or the u. Hum, must track this down.......
------------------------------------------------
The same abstract was repeated twice - the one about cabbage becoming
mycorrhizal, so only the one paper supporting the only that this one cabbage can be
mycorrhizal.

Do you know who it is that suggested to these people to do this research? I
suspect the reason they looked at this is because of a discussion I had with
researchers in South Africa the first time I went there (back in 1998 or
thereabouts), and pointed out that we see mycorrhizal colonization on roots of
brassica on occassion, and that the relationship does not seem to be detrimental at
all, but beneficial.

What we still can't really state clearly, even based on their work, is
whether VAM colonization is beneficial by itself, or whether the roots were ALSO
colonized by OTHER fungi that we know enhance anti-oxidative enzymes, which
strongly influence disease suppression. VAM colonization often enhances
colonization by other beneficial organisms. So, was it VAM actually doing the work, or
VAM mediating the benefit from other organisms?

Will benefit last through the whole life of the plant, and what happens when
the plants are grown in the real world? The Allens work suggests that VAM
plants force mycorrhizal colonization on brassica, and thus suck nutrients from
the brassica, helping out the true mycorrhizal plant, while draining the
brassica to death. Plant vampires?

So, just because a brassica can become mycorrhizal, and we see mycorrhizal
colonization, doesn't mean there will be benefit.

The majority of the data in the scientific literature suggests that brassica,
in general, are not mycorrhizal. A few papers (see work by the Allens, and
Brent Reeves) suggest that mycorrhizal colonization is actively detrimental. A
few papers are now suggesting that maybe some brassica can be mycorrhizal.
We need to learn which plants, and under what conditions.

Way too early to say that brassica and VAM plants can be grown together.

And please note, that Dr. Nelson says -
Differential efficiency in mycorrhizal colonization and the specificity of
fungal symbiont to stimulate the growth and nutrient uptake of the host were
observed.

So, which species of brassica MIGHT be benefitted?

More work required.
----------------------
>From a practical point of view, the take-home message is still that most
brassica are not mycorrhizal, and don't become mycorrhizal, and possibly are
actively harmed by being colonized.

As I have pointed out before, SOME brassica CAN BE mycorrhizal in certain
conditions. We have a great deal to learn.

BUT, when in doubt, it is not wise to plant brassica and higher plants in the
same place at the same time, nor to follow a brassica crop with a crop of
something else.

Get rid of the VAM-inhibiting materials, whether in the roots, or in the
soil, by using compost or compost tea to use those food resources, whether they
are chemicals or the root tissue as foods.

Then apply the mycorrhizal fungi, so you know the vegies or row crop or broad
acre plants can become mycorrhizal if they need to become mycorrhizal.

Elaine R. Ingham
Soil Foodweb Inc., Corvallis, Oregon
Soil Foodweb Inc., Port Jefferson, New York
Soil Foodweb Institute, Lismore Australia
Soil Foodweb Institute Cambridge, New Zealand
Laboratorios de Soil Foodweb, Culiacan, Mexico
Soil Foodweb Inc., Jerome, Idaho
Soil Foodweb Inc., South Africa







Received on Tue Nov 02 2004 - 13:14:59 EST

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