Agriculture Reference
In-Depth Information
Nevertheless,.it.is.unclear.how.recombination.would.be.more.likely.to.occur.between.
a. viral. transgene. mRNA. and. an. infecting. virus. than. between. two. viruses. that. are.
coinfecting.the.same.host.(a.common.situation).
2,33-35
.It.is.likewise.unclear.how.recom-
bination.is.any.more.likely.to.occur.in.the.transgenic.case.than.in.the.case.of.cross-
protection,. an.accepted. method. used. in.controlling.viral. diseases..Cross-protection.
relies.on.the.use.of.mild.virus.strains.to.protect.plants.from.economic.damage.caused.
by.closely.related.severe.virus.strains.
36,37
.Therefore,.RNA.molecules.of.distinct.viral.
strains.have.ample.opportunities.to.recombine.in.cross-protected.plants..Though.not.
shown.to.have.emerged.in.cross-protected.plants,.recombinant.viral.strains.resulting.
from. recombination. between.
Arabis mosaic virus
. (ArMV). and.
Grapevine fanleaf
virus
.(GFLV).have.been.observed.
38
.The.use.of.recombinant.mild.strains.of.ArMV.
and.GFLV.to.cross-protect.against.GFLV.is.an.accepted.experimental.control.method.
for.GFLV
39
.despite.their.deliberate.dissemination.in.the.environment.
G
ene
f
low
to
f
ree
-l
IvInG
r
elatIveS
Another.concern,.not.unique.to.virus-resistant.transgenic.crops,.is.the.risk.of.transgene.
low.
2,12,13
.Transgene.movement.from.a.transgenic.crop.species.to.a.free-living.relative,.
through.pollen.low,.can.be.a.signiicant.concern..If.transgenes.provide.a.selective.advan-
tage,.it.is.conceivable.that.hybrids.between.transgenic.and.free-living.compatible.species.
might.acquire.a.itness.beneit.and.eventually.a.competitive.edge.over.free-living.plants.
40
.
In. an. extreme. scenario,. a. transgenic. hybrid. may. outcompete. free-living. plants. and.
thereby.lead.to.an.elimination.of.entire.species,.land.races,.or.varieties.of.non-transgenic.
plants..In.the.case.of.virus-resistant.transgenic.plants,.it.is.postulated.that.a.hybrid.pos-
sessing.a.transgene.conferring.virus.resistance.might.outcompete.compatible.free-living.
plants.and.become.established.in.the.natural.environment..Though.this.is.unlikely.to.be.
due.to.an.increase.in.weediness.potential.of.the.transgenic.crop.itself,.such.a.scenario.
may.have.far-reaching.environmental.consequences.in.the.case.of.free-living.species.
2
The. likelihood. of. outcrossing. between. transgenic. crop. plants. and. free-living.
relatives.depends.on.numerous.factors,.including.pollen.phenology,.pollen.compat-
ibility,.and.spatial.proximity.
40
.Each.of.these.factors.could.vary.signiicantly.between.
any.two.given.transgenic.crop.species.and.environments..Therefore,.evaluations.of.
the.likelihood. of.gene. low.(and.its.effects).must. be.carried. out.on.a.case-by-case.
basis..Even.if.gene.low.from.a.virus-resistant.transgenic.crop.to.free-living.relatives.
could.readily.occur,.it.is.not.obvious.what.effect.this.would.have..Gene.low.from.
domesticated.crop.species.developed.through.traditional.breeding.practices.has.also.
been.shown.to.occur,
40-44
.but.in.the.case.of.traditional.breeding,.problems.arising.
from. gene. low. to. free-living. relatives. have. not. been. seen,. and. it. is. unclear. how.
the.effect.of.transgenic.virus.resistance.genes.would.be.substantially.different.from.
those.of.resistance.genes.derived.from.traditional.breeding.
e
ffectS
on
n
ontarGet
o
rGanISmS
An.additional.concern.regarding.transgenic.horticultural.crops.is.their.potential.to.
have. negative. effects. on. nontarget. organisms,
2,45
. for. example,. organisms. that. are.
not. intentionally. targeted. by. the. disease. or. pest. management. strategy.. Effects. on.
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