Symmetric and Asymmetric Somatic Hybridization in Citrus: review
Claudine M. de Bona, Dayse C. de Carvalho, David M. Stelly, J. Creighton Miller Jr. & Eliezer S. Louzada
Somatic hybridization by nuclear or cytoplasmic fusions leads to three distinct possible outcomes -- [a] “symmetric” hybrid: fusion of whole nuclei, [b] “asymmetric” hybrid: fusion of parental nuclei, one or both deficient for one or more chromosome(s), and [c] “cybrid”: fusion without a nuclear contribution by one parent, i.e., an extremely asymmetric hybrid. Somatic hybridization in citrus has been a powerful tool for the production of novel allotetraploid somatic genotypes that combine desirable characteristics of two parents. These hybrids open new opportunities for sexual hybridization at the tetraploid level, and for interploid crosses for the production of potentially seedless triploids, among other uses. Somatic symmetric hybrids have great potential for rootstock improvement and are excellent as breeding parents, but they may have limited direct application as scion cultivars because they typically contain the entire genomes of both fusion parents, and are likely to exhibit the desirable and undesirable traits of both parents. Asymmetric hybridization is very promising as it allows partial genome transfer and may be better tolerated than a whole-genome transfer. A brief review about symmetric and asymmetric somatic hybridization and cybridization in citrus is presented. Somatic hybridization seems to be a great tool for citrus breeding. However, the release of new improved cultivars produced by this technology is what is going to prove its effectiveness.