> I wondered about the potential for increased utilization of
> endophytic and epiphytic microbe/plant relationships to manage
> phytophagous insects.
I used to collect literature on this subject, and I think it is possibly
useful, perhaps for more than herbivore control. Here is the abstract of a
paper I found a while back:
"The filamentous fungal ascomycete Colletotrichum magna causes
anthrancnose in cucurbit plants. Isolation of a nonpathogenic
mutant of this species (path-1) resulted in maintained wild-ty
levels of in vitro sporulation, spore adhesion, appressorial
formation, and infection. Path-1 grew throughout host tissues
as an endophyte and retained the wild-type host range, which
indicates that the genetics involved in pathogenicity and host
specificity are distinct. Prior infection with path-1 protected
plants from disease caused by Colletotrichum and Fusarium.
Genetic analysis of a cross between path-1 and wild-type strains
indicated mutation of a single locus." (Freeman, S;Rodriguez, R, J
1993. Genetic Conversion of a Fungal Plant Pathogen to a
Nonpathogenic, Endophytic Mutualist. Science 260:75-78)
I'll bet that under breeding and selection, some of the changes that occur
in crop varieties result from changes in the endophyte. Since most
endophytes are passed through the seed, genetic changes or selection among
strains could masquerade as genetic change in the plant. Fusarium
moniliforme, for example, is practically an endophyte in corn. The
relationship is highly evolved, and from an evolutionary perspective, F.
moniliforme and related species might be on the road to becoming
full-fledged endophytes. There is tremendous diversity in this portion of
the Fusaria. My impression from cutting up a lot of corn stalks is that
good corn varieties are able to keep the fungus under control and mostly
confined to the lower few internodes until late in the life cycle of the
plant. Maybe seed-transmitted hypovirulent strains exclude more harmful
strains from the cornstalk niche?
> What would be the benefits of having an endotoxin synthesized
> by an endophytic organism rather than by the plant itself ?
You could produce improved strains of endophytes and market them as seed
> What would be the benefits of having an endotoxin synthesized by
> an adapted epiphytic microbe rather than the host plant ?
Obviously it would facilitate use, since you would only need to treat the
seed with the agent rather than breed the trait into the variety.
This was done about ten years ago using a bacterial endophyte from
bermudagrass as a vector for Bt in corn:
"The field efficacy of the endophytic bacterium Clavibacter xyli subsp.
cynodontis (Cxc) expressing the cry-IA(c) insecticidal protein gene of
Bacillus thuringiensis (Bt) was evaluated against European corn borer
(Ostrinia nubilalis) (ECB) in field corn during 1990 in Maryland and during
1991-1993 in Nebraska. The engineered strains, referred to as Cxc/Bt, were
introduced into corn seedlings using a wound inoculation technique or into
corn seed via pressure infiltration technique. Two Cxc/Bt strains (MDR1.586,
MDR1.1413) were evaluated in the pedigree LH119 x LH82. Plants were
artificially infested near pollen shed with neonate EGB larvae and later
dissected to determine the amount of ECB tunneling. In 1993, plots were
machine-harvested to obtain yield data. Both Cxc/Bt strains significantly
reduced ECB damage compared with plants colonised by wild-type Cxc and/or
uncolonized control plants. In 1990, stain MDR1.586 reduced the number of
tunnels by 64.0%. Field efficacy of strain MDR1.586 was further demonstrated
in 1991 and 1992 as treated plants exhibited 57.1 and 65.0% fewer tunnels,
respectively. Strain MDR1.1413 reduced the number of tunnels by 79.0% in
1992 and by 68.7% in 1993. Despite the significant control of ECB by strain
MDR1.1413 in 1993, grain yield from Cxc/Bt-inoculated plants was not
significantly different from the uninoculated control." (AU: Tomasino,-S.F.;
Leister,-R.T.; Dimock,-M.B.; Beach,-R.M.; Kelly,-J.L.
TI: Field performance of Clavibacter xyli subsp. cynodontis expressing the
insecticidal protein gene cryIA(c) of Bacillus thuringiensis against
European corn borer in field corn.
SO: Biol-control. Orlando, Fla. : Academic Press, Inc. Sept 1995. v. 5 (3)
I suspect this approach didn't work as well as Bt in the plant genome.
PS: People with tall fescue pasture need to be aware of the danger from
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