Citrus somatic hybridization and cybridization via protoplast fusion has be
come an integral part of citrus variety improvement programs worldwide. Cit
rus somatic hybrid plants have been regenerated from more than 200 parental
combinations, and several cybrid combinations have also been produced. App
lications of somatic hybridization to citrus scion improvement include the
production of quality tetraploid breeding parents that can be used in inter
ploid crosses to generate seedless triploids, and the direct production of
triploids by haploid + diploid fusion. Applications of somatic hybridizatio
n to citrus rootstock improvement include the production of allotetraploid
hybrids that combine complementary diploid rootstocks, and to combine citru
s with sexually incompatible or difficult to hybridize genera that possess
traits of interest for germplasm expansion. A few somatic hybrid tetraploid
breeding parents have flowered, are fertile, and are being used as pollen
parents to generate triploids. Several allotetraploid somatic hybrid rootst
ocks are performing well in commercial field trials, and show great promise
for tree size control. Seed trees of most of these somatic hybrid rootstoc
ks are producing adequate nucellar seed for standard propagation. Somatic h
ybridization is expected to have a positive impact on citrus cultivar impro
vement efforts.