Volume 30 Number 1 Article 23 Pages: 23-23
Year 1976 Month 1
Title: Cytological Diploidization of the Cultivated Octoploid Strawberry - Fragaria xananassa Duch.
Authors: D. Byrne and G. Jelenkovic
Citation
Abstract:
Fragaria xananassa Duch. (2N =
8x = 56) is a hybrid species derived
from a cross between two other octoploid
species, F. virginiana L. and F.
chiloensis Duch.
Evolutionary studies
have shown that these octoploids
evolved by processes of both autopolyploidy
and allopolyploidy from
three ancestral diploid species.
The
genomic constitution of the octoploid
strawberries is thought to be a AAA-
'A'BBBB (Senanayake and Bringhurst,
1967). Since there are four B genomes,
multivalent formation would
be expected during meiosis.
There have been conflicting reports
concerning the meiotic chromosomal
behavior of F. xananassa Duch.
Ichijima
(1926), Longley (1926) and
Powers (1944) have reported regular
bivalent formation during meiosis
whereas Mok and Evans (1971) frequently
observed multivalent configurations
during diakinsis.
In our investigation, seven genotypes
of the cultivated strawberries
and nineteen plants from several S1
progenies were studied meiotically.
No genuine multivalents were found
and all the genotypes had bivalent
pairing during meiosis.
One plant had
bivalent pairing during zygotene and
pachytene and during diplotene almost
complete to complete desynapsis
occurred.
It was therefore concluded
that F. xananassa Duch. is diploidized.
In order to determine whether the
genomes from the ancestral diploids
have retained some of their homology
for each other, several pentaploids
(2N = 5x = 35) derived from crosses
between F. xananassa Duch. and F.
nubicola Lindl. (2N = 2x = 14) were
studied.
The fact that more than
seven bivalents and multivalents were
observed during meiosis indicates that
there is autosyndetic pairing between
the chromosomes contributed by F.
xananassa Duch.
Since homology does
exist between these genomes, a genetic
control mechanism over diploidization
in the octoploid is indicated.
This would mean that F. nubicola
Lindl. has a gene(s) which suppresses',
the octoploid's genetic control of chromosomal
pairing.
Such systems have
been observed in some wheat hybrids.
A critical test of this would be the
meiotic study of a polyhaploid derived
from F. xananassa Duch.
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