Agriculture Reference
In-Depth Information
host.cell.during.the.irst.stages.of.canker.formation.
131,132
.The.cytoplasm-expressed.
antibody.fragment.should.bind.to.PthA.upon.delivery.into.the.host.cell.and.prevent.
its.nuclear.localization..This.strategy.did.not.produce.fully.resistant.plants.but.was.
eficient.in.slowing.the.disease.process,.resulting.in.a.2000-fold.reduction.in.the.
number.of.
X. citri
.cells.released.after.one.cycle.of.infection..Complete.immunity.
is.considered.possible.by.improving.the.stability.and.expression.level.of.the.recom-
binant.antibody.
133
Fungal Resistance
Venturia inaequalis
Apple.scab,.caused.by.the.fungal.pathogen.
Venturia inaequalis
,.is.a.serious.dis-
ease.in.almost.all.apple.cultivars.grown.commercially.around.the.world.and.causes.
signiicant. losses. worldwide.. A. scab. resistance. locus,.
Vf
,. has. been. identiied. in.
the.crabapple.species.
Malus loribunda
.
134
.The.
Vf
.locus.confers.resistance.to.ive.
races. of.
V. inaequalis
135
. but. not. to. races. 6. and. 7,. identiied. in. Europe.
105,136,137
.
A number.of.other.scab.resistance.genes.have.been.mapped.onto.the.apple.genome,.
but.only.the.
Vf
.locus.has.been.analyzed.in.detail..
Vf
.is.a.complex.locus.contain-
ing. four. paralogs,.
Vfa1
,.
Vfa2
,.
Vfa3
,. and
Vfa4
.
138,139
. HcrVf2,. a. homolog. to. the.
Cladosporium fulvum
.resistance.gene.of.tomato,.was.transformed.into.the.'Gala'.
cultivar. of. apple,. conferring. scab. resistance.
140
. In. addition,. the.
Vfa1
,.
Vfa2
,. and.
Vfa4
.genes.were.introduced.into.a.plant.cloning.vector,.pCAMBIA2301,.and.used.
for.
Agrobacterium
-mediated.transformation.of.'Galaxy'.and.'McIntosh'.apple.cul-
tivars.. Transformed. lines. expressing.
Vfa1
. and.
Vfa2
. exhibited. partial. resistance.
to.apple.scab,.while.transformed.lines.expressing.
Vfa4
.were.found.to.be.suscep-
tible.to.apple.scab.
141
.The.stilbene.synthase.(
Vst
)gene.from.
Vitis vinifera
.L..is.also.
being.used.to.transform.apple.with.apple.scab.resistance.
142
.Alternative.approaches.
to. engineer. resistance. include. expression. of. an. antimicrobial. peptide,
143,144
. chi-
tinases,
96,145,146
. exochitinases,
147-149
. and. endochitinases.
147,150,151
. Transgenic. apple.
plants. expressing. high. levels. of. endochitinase. are. resistant. to.
V. inaequalis
,. but.
are. also. stunted.
150
. One. promising. strategy. for. breeding. durable. scab. resistance.
is.to.combine.several.functionally.different.resistance.genes.into.a.single.cultivar.
(pyramiding.of.resistance.genes).
105,152,153
Botrytis cinerea
Gray.mold,.caused.by.
Botrytis cinerea
,.attacks.the.shoots,.leaves,.lowers,.and.fruits.
of.grape,.tomato,.and.strawberry,.as.well.as.other.crops..It.is.one.of.the.most.destruc-
tive.fruit.diseases,.resulting.in.signiicant.economic.losses.pre-.and.postharvest..The.
most.common.strategy.to.control.
B. cinerea
.is.the.regular.application.of.fungicides.
throughout. lowering.. However,. new. strategies. utilizing. PGIPs,. cell. wall. proteins.
that.can.inhibit.fungal.polygalacturonases,.have.been.shown.to.be.effective.in.con-
trolling.
B. cinerea
.
154
.Transgenic.expression.of.pear.PGIP.in.tomato
155
.and.grape
117
.
limits.fungal.colonization.by.inhibiting.fungal.polygalacturonases,.reducing.suscep-
tibility.to.
B. cinerea
..Strategies. based.upon.altering.the.expression.of.native.plant.
cell. wall-modifying. enzymes. have. also. proved. effective. in. controlling. gray. mold..
For. example,. suppression. of. the. endo-beta-1,4-glucanases. Cel1. and. Cel2. reduces.
gray. mold. in. tomato.
156
. Likewise,. simultaneous. suppression. of. genes. encoding.
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