Exploitation of protoplast-to-plant system
Citrus
Limitations of citrus breeding:
Polyembryony, pollen–ovule sterility, sexual and graft incompatibilities, and
extended juvenility.
Applications of Somatic hybridization in citrus
A. Ploidy manipulation in scion improvement
i. Somatic Hybridization is used for seedless citrus production

To generate triploids via:
o Fusion of complementary elite diploid scions into allotetraploid somatic
hybrids. Flowering somatic hybrids are being used as breeding parents in
interploid crosses with selected complementary diploid parents to generate
triploid progeny. (Tetraploids grow slowly, bear less fruits than diploids of the
same spp.)
o the direct production of triploids by haploid + diploid fusion

Cybridization:
Transfer of cytoplasmic male sterility from Satsuma orange to other elite
seedy scions via cybridizaion
ii. Improvement for Quality traits
Easy-peeling, good external/ internal color, good flavor, a range of maturity
dates, and good shipping ability/shelf-life.
For acid lemon/lime improvement: primary breeding objectives include
improved cold-hardiness and disease resistance (citrus canker, citrus tristeza
virus, and witches broom), and potential new industrial oils.
B. Rootstock improvement:
The primary objective of rootstock breeding program is packaging the necessary
biotic and abiotic resistances together with wide soil adaptation, productivity, and
the ability to control tree size.
Hence, SH is exploited for:
i.
Breeding rootstocks at the tetraploid level
a. Production of ‘tetrazygs’
Conventional crossing of somatic hybrids at tetraploid level to produce ‘Tetrazyg’
(allotetraploid sexual hybrids). This is a good example of combining biotechnology with
traditional breeding methods.
Examples:
1.
C. sinensis (Caipira sweet orange) + C. Limonia (Rangpur lime)
(2n=4x=36) SHs are potential rootstocks for the citrus industry in Southeast Brazil because
they may combine drought tolerance and growth vigour of lime with blight tolerance of
Caipira sweet orange
C. sinensis +C. volkameriana,
C. reticulate + C. Jambhiri
C. aurantium with C. Limonia
with potential tolerance to blight and tristeza virus

Genetic and genomic studies, and consequent breeding potential, of citrus somatic
hybrids:
a. RAPDs, SSR, AFLP to diversity estimation
b. CAPS analysis for organelle genome analysis
Success Stories in Citrus : A key and generally unusual feature of Citrus compared to other
genera is the ease with which interspecific and intergeneric somatic hybrids can be
produced, with wild relatives of cultivated Citrus representing an untapped gene pool
reservoir to generate novel somatic hybrid and cybrid plants.
I.
CREC, UFl, USA reported 9 new somatic hybrids and 5 autotetraploids produced by
protoplast fusion, with focus on the zipper-skin trait (Grosser et al. 2010).
II.
More than 100 such somatic hybrid rootstock combinations have been produced,
propagated by rooted cuttings, and many have been entered into commercial field
trials
III.
The program was initiated at the CREC in 1999, and so far more than 600 genetically
diverse ‘‘tetrazyg’’ hybrids have been selected for further evaluation.