Citrus scion and rootstock improvement via somatic hybridization

The technique of protoplast fusion has been used to produce numerous somatic hybrids that have potential in citrus scion and rootstock imrovement, including interspecific hybrids, and intergeneric hybrids between both sexually compatible and incompatible parents. The general method used to generate somatic hybrids is polyethylene glycol (PEG)-induced chemical fusion of competent protoplasts isolated from nucellus- derived friable embryogenic callus or suspension cultures of one parent with protoplasts of a second parent isolated from seedling leaves. Somatic hybridity is verified by chromosome number determination in combination with electrophoretic analyses of either isozymes or DNA banding patterns. Strategic for the application of somatic hybridization to citrus rootstock improvement include the production of allotetraploid hybrids that combine complementary rootstock genotypes and wide hybridization of with species from related genera that possess traits of interest. The strategy for scion improvement is the production of interspecific somatic hybrids that combine complementary parents for use in interploid crosses to generate seedless triploid zygotic progeny. This review will describe the somatic hybrids produced to date and discuss their potential value to citrus scion and rootstock improvement. Preliminary observations on somatic hybrid fertility and field performance will also be presented.