It would work if a related plant were sprayed with a mildew from a closely
related species. Most fungi don't cause disease on most plants. In fact, most
fungi don't react to most plants at all (and vice versa). In order for the
mildew to cause a reaction (induced systemic resistance, or systemic acquired
resistance) on a plant, it must recognize "something" on the leaf surface
(usually a protein, or cuticular component) and germinate, then the plant would
react to the mildew. There are (as Dale points out) certain chemicals that
cause plants to turn on these universal defenses (Actiguard, by Novartis, is
one. Salicylic acid is another component, phosphoric acid is a third). Also,
physical damage to plant can induce some plant protective compounds. Mildews
are just too specific.
The important thing to remember is that most plant pathogens don't cause plant
disease on most plants. Disease is always the exception. Reactions to
pathogens go from none to resistant reactions to susceptible reactions
(disease). These, while definable, are arbitrary labels, and a continuum
exists.
There is also a range of disease causing organisms. Mildews and rusts are known
as biotrophs. They require a living host to provide nutrients, and cannot be
grown on artificial media. Mildews usually (and there are always exceptions)
have a race-cultivar type of interaction. That is, a race of one species of
mildew will grow on a specific cultivar of host, and not another cultivar of the
same host species. (this is a generalization, since there are all sorts of this
type of interaction, including species-species, species-genus, etc.) Rusts are
usually the same way. Sclerotium rolfsii, on the other hand is a necrotroph,
deriving it's nutrient from the dead host cells. Sclerotium rolfsii has more
than 500 host species. These are extremes for generalizations. The world isn't
so simple.
One genus (Phytophthora) has several species that can attack a large number of
plant species (P. cinnamomi, P. parasitica, P. cactorum, and P. nicotianae) and
one species that attacks only two species (P. infestans, causes late blight of
potato and tomato).
Wow, that was a lot longer than I thought it was. For those that are still
reading, I apologise for the impromptu lecture on plant pathology, and thank you
for your attention. I'll step down from my soapbox now. . .Russ
"Wilson, Dale" wrote:
> Russ,
>
> Frits wrote:
> >> Then spray the cultivated plants with this and wait for the natural
> >> reaction from the plants or from other fungi that protect the plants
> >> by destroing the mildew.
>
> You wrote:
> > this would be a good idea. No harm will come to your crop,
> > and the sensitive weed may succumb to mildew. . .Russ
>
> That is not what Frits was getting at. He wants to induce resistance to
> pathogenic strains of mildew by spraying with nonpathogenic strains. That
> is a neat idea, maybe it can work. There are chemicals that induce systemic
> resistance when sprayed on plants. This is a hot topic in the ag chemical
> industry, and we are trying out an inducer to control rust and other
> diseases in corn seed production. Jasmonate and salicylic acid are
> inducers, and I have heard (but not tried) that aspirin does interesting
> things on plants (including killing at sufficient dose).
>
> Dale
-- Russ Bulluck Ph.D. Candidate Department of Plant Pathology North Carolina State University PO Box 7616 Raleigh, NC 27695-7616http://www.cals.ncsu.edu/plantpath/Personnel/Students/webpage.htm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The soil population is so complex that it manifestly cannot be dealt with as a whole with any detail by any one person, and at the same time it plays so important a part in the soil economy that it must be studied. --Sir E. John Russell The Micro-organisms of the Soil, 1923 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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