PCR Primers for Marker Assisted Backcrossing to Introduce a CTV Resistance Gene from Poncirus trifoliata (L.) Raf. into Citrus

Citrus tristeza virus (CTV) is an acute pathogen that causes serious damage to the citrus industry. Poncirus trifoliata (L.) Raf., a sexually compatible species with Citrus, has resistance against a broad range of CTV strains. Breeding programs have been conducted to introduce the CTV resistance gene from P.trifoliata to Citrus, but no commercial cultivar has yet been developed. In this study, we developed four selection markers linked to CTV resistance to enable marker assisted selection to efficiently introduce CTV resistance into Citrus. The four CTV resistance-linked markers were composed of a co-dominant single nucleotide polymorphism (SNP) marker and three dominant sequence tagged site (STS) markers. All four markers were fitted to the progeny and were linked to CTV resistance, with only 2.8% exceptions. We also developed 46 P.trifoliata allele identification markers from alleles of 35 Citrus species. Among the 46 markers, nine were located in linkage group 2, on which the CTV resistance locus is located. We located the other 31 markers on the rest of the linkage groups so that these markers could be used to distinguish P.trifoliata genome regions remaining in the hybrid progenies. The set of PCR primers developed in this study will be useful for marker assisted backcrossing to introduce the P.trifoliata CTV resistance gene into Citrus.

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