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Nucellar Embryony in Citrus Rootstock Breeding






In citrus, nucellar embryony is generally essential in citrus rootstocks because it

 

 
 

Fig. 5.1. Multiple seedlings emerging from a citrus seed.


 

© CAB International 2007. Citrus Genetics, Breeding and Biotechnology (ed. I.A. Khan) 141


 

 

allows nurseries to propagate trees on highly heterozygous, but genetically uni- form seedling populations. This reduces variation in rootstock and scion perform- ance in comparison with that which would occur if rootstock seedlings resulted from sexual reproduction. Nucellar embryony allows citrus rootstock breeders to produce F1 hybrids that are highly heterozygous, but produce seedlings that are genetically uni- form and identical to the mother tree. If nucellar embryony were not present, citrus breeders and nurseries could take several different approaches to produce genetically uniform rootstocks. Rootstocks could be vegetatively propagated as rooted cuttings or propagated using in vitro culture meth- ods. Another alternative would be to use seedling populations of genotypes that are homozygous for all important traits. Although these strategies are used in other tree crops and have been attempted in citrus, none has been commercially suc- cessful, perhaps because they are more dif- fi cult or costly to implement than growing nucellar seedling populations of citrus root- stocks. Therefore, nucellar embryony is considered an essential trait in citrus root- stocks. The rootstock breeder must there- fore choose parents that produce progeny having the trait, and must select progeny that produce a high proportion of nucellar seedlings and few sexual seedlings.

 

 


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