Transgenic Fruit Crops in Europe - Transgenic Horticultural Crops: Challenges and Opportunities - page 135

900.m 2 . (B/IT/98/26).. The. GM. kiwifruit. plants. expressed. either. the. rol . genes. of.
Agrobacterium rhizogenes .or.an.osmotin.gene.expected.to.confer.resistance.to.fun-
gal. pathogens.. The. ield. trials. were. focused. on. the. effect. of. transferred. genes. to.
fungal.diseases'.resistance.or.to.the.rooting.ability.of.the.transformed.plants..The.
commercial.use.of.GM.kiwifruits.in.Europe.is.not.to.be.expected.in.the.near.future.
p ear
In. Europe,. only. one. summary. notiication. was. found. for. a. pear. rootstock.. The.
intended.ield.trial.(B/SE/04/1227).was.carried.out.in.Sweden..The.GM.plants.con-
taining.the. rolB .gene.of. Agrobacterium rhizogenes .were.planted.at.the.same.place.
as.the.transgenic.apples.
The.GM.pear.plants.have.an.improved.rooting.ability..The.purposes.of.the.ield.
trial.were.the.evaluation.of.the.effects.of.the.transgenic.rootstocks.on.growth,.lower-
ing,.fruit.set.and.fruit.quality.of.grafted.cultivars,.the.stability.of.the.modiied.trait.
(rooting.ability),.and.the.rooting.ability.of.the.transgenic.rootstocks.themselves.by.
stooling..GM.pears.are.still.quite.a.long.way.from.commercial.use.
p lum
The.most.important.agronomic.trait.in.plum.is.virus.resistance,.especially.to. Plum
pox virus .( PPV ),.the.etiological.agent.of.sharka.disease,.which.is.one.of.the.most.
devastating. pathogens.. Sharka. disease. can. cause. extensive. economic. losses. 29,30 .
Furthermore,.the.virus.has.quarantine.status.in.many.countries. 31 .In.Europe,.there.
are.about.100.million.stone.fruit.trees.currently.infected.with.the.virus. 32 .Breeders.
are. always. anxious. to. develop. resistant. cultivars,. but. breeding. of. sharka-resistant.
plums.is.dificult.. PPV .resistance.is.often.polygenic.and.in.addition.may.be.strain.
speciic.. The. long. juvenile. period. of. seedlings. hampers. the. success. of. traditional.
breeding. programs. considerably.. Genetic. engineering. offers. an. exciting. tool. to.
overcome. some. of. the. existing. problems.. Several. recent. studies. have. focused. on.
overexpression. of. coat. proteins. of. the. PPV . 33,34 . The. transgenic. line. C5. (named.
'HoneySweet').was.selected.because.of.its.high.level.of.resistance..This.line.con-
tains.a.multicopy.insert.of.the. cpPPV .gene.that.acts.as.a.single.locus..The.expres-
sion.level.of.this.gene.is.reduced.in.HoneySweet,.a.result.of.posttranscriptional.gene.
silencing. (PTGS). (reviewed. in. Scorza. and. Ravelonandro 31 ).. Based. on. inoculation.
studies,.it.was.found.that.HoneySweet.is.highly.resistant.to.the.major.serotypes.of.
PPV ..The.stability.and.durability.of.the.PTGS-based. PPV .resistance.of.HoneySweet.
was.tested.in.ield.trials.in.different.countries.for.a.number.of.years. 35-37 .Since.the.
early.1990s,.ield.trials.with.HoneySweet.have.been.performed.in.Europe.and.the.
United. States.. In. Europe,. a. total. of. ive. summary. notiications. can. be. found. for.
GM. plums. (http://bgmo.jrc.ec.europa.eu/deliberate/dbplants.asp).. Field. trials. with.
HoneySweet.were.performed.in.Spain.(two),.in.Poland.(one),.in.the.Czech.Republic.
(one),.and.in.Romania.(one).
Based. on. the. results. obtained. with. HoneySweet,. a. petition. for. deregulation.
was.approved.in.the.United.States.in.June.2007. 38 .The.Animal.and.Plant.Health.
Inspection. Service. (APHIS). of. the. U.S.. Department. of. Agriculture. (USDA).