Somatic hybridization via protoplast fusion has become a
relevant biotechnology that facilitates ploidy manipulation
in efforts to develop improved plant cultivars. Initial successes
have been primarily to access disease resistance
genes from related wild species that are difficult or impossible
to hybridize by conventional breeding methods.
Although not apparent at the onset, the most important
application of the technique may be the production of novel
breeding parents for use in unique conventional breeding
strategies. In the CREC citrus breeding program, somatic
hybridization is having a profound impact on fresh citrus
cultivar development through production of superior tetraploid
breeding parents via symmetric fusion of elite diploid
cultivars, followed by interploid crosses to generate seedless
triploids for mandarin, grapefruit/pummelo and acid lemon/
lime improvement. Due to the heterozygous nature of allotetraploids
obtained via somatic fusion, greater genetic
and phenotypic diversity can be found from interploid
conventional crosses using the somatic hybrid allotetraploid
as compared to an autotetraploid parent. The evaluation of
numerous interploid crossing combinations can lead to the
identification of superior allotetraploid parents that should
contribute to rapid progress in the development of improved
seedless fresh fruit citrus cultivars.
For rootstock improvement, feedback from the field
evaluation of somatic hybrid rootstocks has identified
superior parents for use in a unique tetraploid rootstockbreeding
program that maximizes genetic diversity in tetraploid
zygotic progeny. Evolving screening methodologies
are facilitating efficient identification of superior hybrids
for ongoing greenhouse and field evaluations. Currently
available EST-SSR genotyping techniques are being utilized
to determine unambiguously seedling type (nucellar or
zygotic origin), and whether candidate rootstocks are
amenable to traditional nursery propagation method. Continued
research should result in the release of improved,
widely adapted ‘‘tetrazyg’’ rootstocks that exhibit all
required disease tolerance/resistance and tree size control.
In this regard, the approaches outlined here could be
adapted to other commodities with similar breeding objectives,
especially avocado, grape, and some tropical fruit
species, as well as other commodities that utilize rootstocks.
Acknowledgments Much of the research reported herein was supported
by grants from the Florida Citrus Production Research Advisory
Council, NVDMC (The New Varieties Development and
Management Corporation through the Florida Dept. of Citrus) USDA/
CSREES, and by the Florida Agricultural Experiment Station