Gametic configuration and inheritance of SSR markers in tetraploid interspecific and intergeneric ci

Citrus somatic hybridization has become an integral part of citrus improvement programs worldwide. More than100 somatic hybrids have been created by Cirad. Intra and interspecific somatic hybrids will be used mostly forthe triploid scion breeding. Intergeneric somatic hybrids can have a direct application as rootstocks or be usedas parents for sexual ‘tetrazyg’ breeding. To optimize the design of such breeding schemes, it is essential to haveknowledge of the inheritance mode in such allotetraploid hybrids. The aim of the present study was to investigatethe inheritance (disomic, tetrasomic or intermediate) in a citrus interspecific hybrid (Citrus reticulata x Citrus limon)and an intergeneric somatic hybrid (C. reticulata x Poncirus trifoliata). Two triploid populations were generatedusing the somatic hybrids as pollinators in crosses with the diploid ‘Chandler’ pummelo. The triploid progenieswere genotyped with SSRs to infer the allelic constitution of the somatic hybrid gametes. A likelihood-basedapproach was used to estimate for each locus the proportion of disomic versus tetrasomic segregations. For thetwo somatic hybrids, intermediate inheritance was observed with a major tendency for tetrasomic segregationin the interspecific hybrid, but a tendency for disomic inheritance in the intergeneric hybrid. The implications ofthe observed inheritance mode for citrus breeding are discussed with special focus on heterozygosity restitution.