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The meiotic analysis of the hybrid
T. timopheevii var. zhukovskyi x Secale
cereale1)
P.J. SALLEE and G. KIMBER
Department of Agronomy, University of Missouri columbia,
Missouri 65201 U.S.A.
The species Triticum timopheevii var.
zhukovskyi is unique amongst the polyploid wheats in
that it is an autoallohexaploid. The genomic analysis of
this relatively newly identified species was undertaken by
UPADHYA and SWAMINATHAN (1963 and 1965). They concluded that
it had arisen as a result of hybridization and amphiploidy
between T. monococcum and T. timopheevii. This
conclusion is supported both by the sympatric distribution
of these two species and the morphology of
zhukovskyi. Thus, genomically, it would be AAAABB (or
AAAAGG). The hybrid T. timopheevii var.
zhukovskyi x T. monococcum has not been made,
and thus the conclusions are based on the indirect evidence
of comparisons of the meiosis of hybrids T.
timopheevii x T. monococcum, T.
timopheevii var. zhukovskyi x T.
timopheevii and T. aestivum x T.
timopheevii var. zhukovskyi. The evidence showing
that the A and not the B genome is duplicated rests mainly
on comparisons of satellite morphology by UPADHYA and
SWAMINATHAN (1963). Hybrids that will allow the resolution
of this situation have been made by the present authors and
will be reported upon later.
Fig.1. First meiotic
metaphase. Left: T. timopheevii var.
zhukovskyi x Secale cereale, 11I
+7II+1III Right: T. timopheevii
var zhukovskyi,
2I+17II+1IV
Clear recognition of the presence of a duplicated genome in
zhukovskyi is difficult because the formation of
quadrivalents does not reach expectation (UPADHYA and
SWAMINATHAN, 1963). In induced autotetraploids in the genus
the frequency of multivalents also does not reach the
theoretical expectation (KIMBER and LARSON, 1973) with
approximately 50% of the possible multivalents being
observed. Further, polyhaploids of zhukovskyi, which
would allow the easy recognition of a duplicated genome, are
unknown. However, it is possible to make a hybrid situation
which, in some ways, simulates a haploid. By crossing T.
timopheevii var. zhukovskyi with an unrelated
species, the genomes of zhukovskyi are rendered
effectively hemizygous and any duplicated genome should be
recognized by bivalent formation. At first metaphase of
meiosis in the hybrid T. timopheevii var.
zhukovskyi x Secale cereale (Table
1), the number of paired chromosomes per cell
approximated to 14 (the equivalent of seven bivalents). In
fact, in only one cell were there more than 14 univalents,
and in both cells with only four bivalents two multivalents
were also recorded. Clearly the chromosome pairing in this
hybrid is consistent with the hypothesis of a duplicated
genome in T. timopheevii var. zhukovskyi.
Interestingly the presence of trivalents and quadrivalents
must indicate translocations between chromosomes of the
genome that is duplicated in the hybrid and that which is
hemizygous.
The meiosis of T. timopheevii var. zhukovskyi
is tabulated in Table 2.
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