Transgenic Fruit and Nut Tree Crops Review - Transgenic Horticultural Crops: Challenges and Opportunities - page 9

Plum Pox Virus
Sharka,.or.plum.pox,.caused.by.the. plum pox virus .(PPV,.genus.Potyvirus),.is.one.
of. the. most. serious. diseases. for. Prunus . stone. fruit. and. nut. species.. This. virus.
has.caused.serious.economic.losses.to.the.stone.fruit.industry.in.Europe, 71,72 .and.
may.eventually.spread.widely.throughout.North.America.and.South.America. 73-75 .
Prune dwarf virus .(PDV),. prunus necrotic ringspot virus .(PNRSV),.and. tomato
ringspot virus .(ToRSV).are.other.viruses.widespread.in.production.areas.world-
wide. that. are. very. destructive. for. peach,. plum,. cherry,. and. apricot. production..
Viruses. endemic. to. North. America,. including. peach mosaic virus . (PMV). and.
American plum line pattern virus . (APLPV),. are. also. known. to. cause. important.
diseases.of.stone.fruit. 76,77
PPV.mainly.infects.plum,.apricot,.and.peach.trees. 72,78,79 .Sharka.disease.symptoms.
range.from.weak.necrosis.on.leaf.blades.and.stems,.to.death.of.young.shoots..PPV.is.
transmitted.by.aphids.in.a.nonpersistent.manner,.its.main.vectors.being. Myzus persicae .
and. Aphis spiraecola . 80-83 .Due.to.the.severe.economic.losses.in.crop.production.for.
the. stone. fruit. industry,. efforts. have. focused. on. the. development. of. PPV-resistant.
Prunus . cultivars. either. by. conventional. breeding. or. by. biotechnology. approaches..
PPV-resistant. plant. selection. by. traditional. breeding. has. not. been. successful,. but.
the. use. of. biotechnology. approaches. to. obtain. resistant. plants. looks. promising..
Pathogen-derived.resistance.to.PPV.has.been.achieved.by.the.introduction.of.either.
wild.type.or.mutated.structural.and.nonstructural. genes.into.host.plants. 38 .A.gene.
silencing. approach 46 . was. used. to. obtain. transgenic. European. plums. carrying. the.
CP.gene.of.PPV..The.diversity.and.dynamics.of.PPV.and.aphid.population.in.trans-
genic. European. plums. has. also. been. evaluated. in. the. ield. during. 7. years. under.
Mediterranean.conditions. 84 .After.7.years.of.experimental.trials,.the.transgenic.line.
C5.(cv..Honey.Sweet).was.reported.to.be.free.from.PPV. 84-86 .The.resistance.mecha-
nism.of.line.C5.was.conirmed.to.be.based.on.PTGS. 46,87
Because.PPV.is.only.one.of.the.multiple.viruses.affecting. Prunus .stone.fruit.pro-
duction,.it.is.highly.desirable.to.engineer.multivirus.resistance.in.plums..Accordingly,.
PTGS-based.approaches.have.been.used.to.provide.multiple.resistances.to.important.
viruses. affecting. Prunus . stone.fruit. and. nut. species.. A. single.chimeric.transgene,.
PTRAP6 ,.was.created.by.the.fusion.of.400-500.bp.long.fragments.from.six.major.
Prunus . fruit. viruses. (APLPV,. PMV,. PPV,. PDV,. PNRSV,. and. ToRSV).. Nicotiana
benthamiana .plants.transformed. with. PTRAP6 .displayed.resistance.to. PDV,.PPV,.
and.ToRSV. 88
Bacterial Resistance
Erwinia amylovora
Fire. blight,. caused. by. the. Gram-negative. bacterium. Erwinia amylovora ,. is. an.
incredibly. destructive. bacterial. disease. of. pear,. apple,. and. other. members. of. the.
Rosaceae . family,. as. well. as. grape..Most. commercially. available. apple. scion. cul-
tivars.and.rootstocks.are.particularly.sensitive.to. E. amylovora ..Resistance.to.ire.
blight. in. apple. and. pear. has. been. engineered. using. several. transgenic. strategies..
Expression. of. the.lytic. peptide.attacin.E. in.transgenic.apples. and.pears.provided.
good. resistance. to. the. pathogenic. bacterium. 89-96 . Other. genes. used. to. improve.