The hunt for allelopathic plants

Thomas Bjorkman tnb1 at cornell.edu
Wed Sep 22 11:52:27 EST 1999


It seems to me that a drawback to this approach is that it may not
demonstrate allelopathy. The particulars of how you do it will be very
important.

One false result would be if you used extract of sugar beet (i.e.
sucrose). Fungal and bacterial pathogens would multiply quickly and reduce
germination. The pathogens are already on the seeds, so sterlilization is
unlikely to be very effective. What you wuold be demonstrating here is
that simple sugars favor pathogens, and that seed rot reduces germination.


The second false result is that many allelopathic agents don't act on
germination. 

For instance, the compound responsible for the classic rye allelopathy
(dibenzoxazolinone) acts on the root meritem. Rye extracts have dramatic
effects on root growth, but little or none on germination. In this case
you would fail to demonstrate allelopathy that was really there.

You can also get a false positive by using root growth, however. If your
extract is high in carbon, microorganisms will take up the carbon faster
thean will the seedling. At the same time, they will take up nitrogen so
they can make protein with the carbon. As a result, the seedling becomes
nitrogen starved. Indeed it can lose a substantial amount of its nitrogen
reserves by leaching. Avoiding this form of growth inhibition is a major
management criterion in agricultural systems using cover crop plowdowns.
Perhaps, if the system is sterilized really well, this could be avoided,
but it is not easy.


In article <7s8sj9$cso$1 at news.henryford.cc.mi.us>, "J. Kelly"
<hfcckelly at hotmail.com> wrote:

> I remember doing a lab in Plant Ecology at where we tested the effects of
> leaf  rinses and leaf extracts on the germination of Jack pine seeds (pinus
> banksiana).  We collected jack pine cones, placed them in an oven at low
> heat to get them to open (they are serotinous cones), and shook out the
> seeds.  We placed the seeds on a layer of washed beach sand in sterile petri
> dishes.  Then we moisted the seeds with a number of different solutions.  We
> homogenized the leaves of wild black cherry (Prunus serotina), reindeer moss,
> and jack pine.  We aslo placed the leaves of these 3 plants in large plastic
> funnels and sprayed water over them to mimic the effect of rain washing
> chemicals off the leaves.  As I remember it worked quite well. Our
> instructor had an article on this, which I believe was from Ecology. You
> might try a an online literature search.
> Good Luck, Judy Kelly, Biology Dept.  Henry Ford college
>
-- 
Thomas Björkman    
Dept. of Horticultural Sciences   
Cornell University



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