| Sumario: | Introduction. In order to apply a marker-assisted selection to the breeding
programs, a review related to the application of the molecular marker technique, used to
study the citrus genetic resources and the resistance to citrus tristeza virus (CTV), was
undertaken. Citrus genetic resources. The citrus germplasm bank at Ivia (Valencia,
Spain) was studied. Six isoenzymatic systems were assayed. A broad spectrum of heterozygosity
values was found in the collection. Two principal groups of Citrus species are
clearly defined: the orange-mandarin group and the lime-lemon-citron-pummelo group.
Genetie differences between species and genera are in general high, which suggest that
adaptation has played an important role during the evolution of the orange subfamily.
CTV resistance. There is an urgent need to diversify the genetic basis of CTV-resistant
rootstocks by developing breeding programs from only CTV-resistant genotypes. Conseq
uently, the first step was to find molecular markers which allow to discard CTVsusceptible
genotypes with a minimum error from large progenies. At least two loci, Ctr
and Ctm, control CTV resistance in Poncirus trifoliata. Utilization of citrus genetic
resources for searching new CTV resistance genotypes. To find out new CTV-resistant
genotypes two searching strategies explained in this paper were evaluated, but only
one has been truly successfu l. Perspectives and further remarks . The rapid advances
of biotechnology give citrus breeders no choice other than to design more efficient
breeding programs. (
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