There have been few studies of meiotic behavior of
citrus somatic hybrids. Fatta Del Bosco et al. (1999)
compared meiosis of diploid Valencia sweet orange
(C. sinensis L. Osbeck) and Femminello lemon (C. limon),
with their somatic hybrid. They concluded that intergenomic
pairing was taking place, based on the increased
frequency of multivalents observed at diakinesis. Also, the
frequency of univalents (as many as 10 univalents per cell
in the hybrid) was found to be intermediate in the hybrid
relative to the parents; as a consequence of pairing
behavior, chromosomally unbalanced gametes were produced
along with a high frequency of polyads. Despite the
variable chromosomal content, pollen germination and
viability were equal or even greater in the somatic hybrid
compared with the diploid donors, so such pollen could be
used to create triploid hybrids. The unbalanced number of
chromosomes in pollen gave rise to backcross offspring
that were concluded to be possibly aneuploid, triploid, and
tetraploid based on measurements of DNA content by flow
cytometry. Although the authors concluded that the sweet
orange and lemon chromosomes were pairing and therefore
presumably undergoing recombination, no information was
provided from either molecular or phenotypic characterizations
to demonstrate this as fact.
More recently, Chen et al. (2008) studied meiosis and
microsporogensis in two additional citrus somatic hybrids,
Hamlin sweet orange ? Rough Lemon (Citrus jambhiri
Lush) (HR) and Key lime (Citrus aurantifolia (Christm.)
Swing.) ? Valencia sweet orange (KV), and their diploid
donor parents. Similar to the results reported by Fatta Del
Bosco et al. (1999), these somatic hybrids also had
increased frequencies of multivalent pairing and univalents,
much lower frequencies of tetrad production, but
sufficient levels of pollen viability and germination to
enable their utilization in hybridizations. These authors,
however, also noted unpublished data from meiotic analysis
of a somatic hybrid of C. reticulata cv. Cleopatra and
Poncirus trifoliata cv. Argentine, the latter being a sexually
compatible genus related to Citrus; in this case, pairing was
characterized by a high frequency of bivalents, perhaps a
There have been few studies of meiotic behavior ofcitrus somatic hybrids. Fatta Del Bosco et al. (1999)compared meiosis of diploid Valencia sweet orange(C. sinensis L. Osbeck) and Femminello lemon (C. limon),with their somatic hybrid. They concluded that intergenomicpairing was taking place, based on the increasedfrequency of multivalents observed at diakinesis. Also, thefrequency of univalents (as many as 10 univalents per cellin the hybrid) was found to be intermediate in the hybridrelative to the parents; as a consequence of pairingbehavior, chromosomally unbalanced gametes were producedalong with a high frequency of polyads. Despite thevariable chromosomal content, pollen germination andviability were equal or even greater in the somatic hybridcompared with the diploid donors, so such pollen could beused to create triploid hybrids. The unbalanced number ofchromosomes in pollen gave rise to backcross offspringthat were concluded to be possibly aneuploid, triploid, andtetraploid based on measurements of DNA content by flowcytometry. Although the authors concluded that the sweetorange and lemon chromosomes were pairing and thereforepresumably undergoing recombination, no information wasprovided from either molecular or phenotypic characterizationsto demonstrate this as fact.More recently, Chen et al. (2008) studied meiosis andmicrosporogensis in two additional citrus somatic hybrids,Hamlin sweet orange ? Rough Lemon (Citrus jambhiriLush) (HR) and Key lime (Citrus aurantifolia (Christm.)Swing.) ? Valencia sweet orange (KV), and their diploiddonor parents. Similar to the results reported by Fatta DelBosco et al. (1999), these somatic hybrids also hadincreased frequencies of multivalent pairing and univalents,much lower frequencies of tetrad production, butsufficient levels of pollen viability and germination toenable their utilization in hybridizations. These authors,however, also noted unpublished data from meiotic analysisof a somatic hybrid of C. reticulata cv. Cleopatra andPoncirus trifoliata cv. Argentine, the latter being a sexuallycompatible genus related to Citrus; in this case, pairing wascharacterized by a high frequency of bivalents, perhaps a
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