[APWG] Ecosystem dynamics and function Allelopathy and sterile hybrids etc. Re: Allelopathic chemicals, Dr. Stebbins, and warning about test plots

[Wayne Tyson]

Craig and Forum:

While I do not always keep strictly up to date on the literature, and would 
no doubt benefit from a refresher, I was hoping for a more focused reference 
to the particular species you mentioned, and the exact allelopathic 
mechanisms involved, the trail of evidence, and a sense of any peer 
comments.

As we all are acutely aware, such things are notoriously difficult to pin 
down with respect to the specific chemistry and its action, so I was hoping 
someone would enlighten me about the particular case of the domestic/feral 
rye, as starting with square one is something I doubt I could finish in my 
lifetime.

I have, like everyone else, observed the apparent effects of phenomena that 
"must be" in the realm of allelopathy, but teasing out the specifics has 
historically been difficult to do. I am certainly willing to invoke 
inference and "common sense," but always welcome proof that those vital 
functions have not once again led me astray from reality. At the very least, 
I would like to eliminate things like vigor, hybrid vigor, density, 
structure, phenological differences, and other factors that influence 
"competition."

Thank you Craig, for the Stebbins references. You are quite right about how 
to check for sterile seeds, although those with apparently good endosperm 
formation (fertile) can have viability problems unrelated to "crossing." 
Populations of Leymus (Elymus) species (E. triticoides) may exhibit 
different degrees of hybridization within and across geographic regions, 
primarily due to two factors: soil fertility (history of disturbance) and 
range overlap of one or more other species (If I recall correctly, Stebbins 
cited both of these in his 1950's era paper[s], specifically in the case of 
E. triticoides and E. condensatus as well as E. glaucus). I have seen large 
clones of both hybrids, which are very vigorous and apparently are limited 
to asexual propagation via rhizomes. Fertile E. triticoides in the same 
region was apparently confined to small, relatively undisturbed refugia, 
smaller in stature and stand density/size, and not as vigorous.

Craig, your information about the need for controls and that a single 
experiment does not necessarily tell the tale, is very solid. However, tests 
in different soils or potting media are limited in the information they can 
supply, while within that scope can be very useful, depending upon the 
information sought. They are poor predictors of how methods will work in the 
field, for example. To test potential field performance of various 
modalities, a lot of repetitions are, as you point out, necessary; in the 
best of worlds, they would go on for years, with both permanent ones and new 
ones added each year. Pretty soon, the test plots become restoration sites. 
Seedling survivorship can be very low in the field, for example, and 
artificially high in the greenhouse; the converse can also be the case.

WT

----- Original Message ----- 
From: "Craig Dremann - Redwood City Seed Company" <Craig at astreet.com>
To: <apwg at lists.plantconservation.org>
Sent: Saturday, August 15, 2009 9:11 AM
Subject: [APWG] Allelopathic chemicals, Dr. Stebbins,and warning about test 
plots


Dear Wayne and All,

Thanks for your emails.

If you check Google Scholar, there are a lot of articles about plant
allelopathy. For example, a good one is The allelopathic phenomenon, a
dynamic process. By Francisco A. Macías, Alberto Oliveros-Bastidas, David
Marín, Diego Castellano and José M.G. Molinillo

http://www.regional.org.au/au/allelopathy/2005/1/2/2647_maciasfa.htm?print=1

This article has details about the natural herbicide-like chemicals
involved, phenols and benzoxazin.

Regarding Dr. Stebbins, there is a list of his papers in chronological
order that I posted on the web when I was co-authoring some native grass
technical papers with him, before he passed away in 2000.  You can see the
list at http://www.ecoseeds.com/stebbins.html

Yes, Dr. Stebbins did find that some populations of native grasses do
produce sterile seeds, especially within some groups.  Elymus, Sitanion,
Bluebunch wheatgrass are populations in the West where that can be found,
but probably only one out of every 100 populations of plants.

It is easy to check for sterile seeds, if you just take your fingernail
and if you do not feel anything hard, the seed did not form.

One of the most interesting papers, that Dr. Stebbins and I published in
1998, is that there are 100 more species of native grasses to be
identified and named here in California.  The 300 current described
California native species were named by physical features in the 1800s
before taxonomists knew about genetics and chromosomes.  Now we need to
tease out of those 300 species of grasses, 100 more, based on chromosome
counts, because they are separate species.

A WARNING about small scale test plots.  While you are sowing your native
seeds in amongst the weeds, at the same time, you absolutely need to set
up two EX-SITU TEST POTS.

What you do is get two 8 inch diameter plastic pot and scrape off the top
inch of soil from the weed site, and fill up one of your pots to within
3/4 of an inch of the top.  In a second pot, you fill it with a commercial
potting mix, I personally like Miracle Grow Organic Choice or their Orchid
potting mix.

Then, at the same time that you sow the native seeds, you also sow some of
the native seeds into your two plastic pots, and take those pots back to
your home or office to keep an eye on.  Give them the same conditions as
your test plot site.

You are doing this to check for soil problems.  If the native seeds grow
in the commercial potting soil, and do not thrive in the weed-soil, then
you may have soil problems.

I was teaching classes to the California Dept. of Transportation
(Caltrans) and the Delaware DOT in 2000 about replacing the roadside weeds
with local natives, and the results of planting in Ex-situ Test Pots was
one of the exercises, that you can see at
http://www.ecoseeds.com/good.example.html

You can see all the Natives for Roadsides DOT training exercises at
http://www.ecoseeds.com/natives.html

And never, ever be the least bit discouraged if your test plots fail the
first time.  Or the second time, or even the third time.  It took UC Davis
three tries and $450,000 to get their native test plots to work and not
get completely eaten alive by the weeds, that you can see at
http://www.ecoseeds.com/road.test.html

Sincerely,  Craig Dremann (650) 325-7333



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