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Results
In PMCs from Frondoso, 21-bivalent configurations were observed,
however, some had a ring or a chain quadrivalent (Fig.1).
Meiotic configurations, differing from a 21-bivalent configuration,
were observed in at least one cell of eight of the 10 Frondoso plants
analyzed (Table1).
In addition to bivalents, univalents and/or quadrivalents were
observed in 37.5% of the cells. A quadrivalent was observed in at
least one cell in seven of the 10 plants analyzed and a quadrivalent
was observed to be present in 6% of the cells analyzed. Twenty-five
percent of the quadrivalents were observed as chains and 75% as
rings. Three of the plants were monosomic and two of these, had a
ring and/or chain quadrivalent along with a univalent in some cells
(Table1).
Discussion
The presence of quadrivalents in Frondoso, at a frequency of 6%,
is comparable to the 10.7% frequency reported by Primard et al.
(1991) for Atlas 66. Love (1951) observed abnormal meiosis in
Frontana, a Brazilian cultivar with the same pedigree as Frondoso,
and Vega and Lacadena (1982) detected quadrivalents in hybrids
produced from crossing Chinese Spring to Mentana, a parent of
Frondoso.
It is possible that Frondoso is a genetically unstable cultivar of
the type described by Suarez et al. (1988). They observed that some
Argentinean wheat cultivars showed aneuploidy at a frequency as hieh
as 27%. Ring and chain quadrivalents were common in these cultivars
and it was suggested that aneuploids arose from an abnormal
regrouping of chromosomes at telophase 1 of meiosis. In addition,
depending on the orientation of a quadrivalent and the occurrence of
crossovers during meiosis, duplicate-deficient gametes, indicated by
a reduction in pollen fertility, can be produced in plants with a
quadrivalent configuration (Burnham 1956). In the present study, no
quantitative data was gathered on the pollen fertility of Frondoso;
however, a number of spikes on various plants were observed to be
infertile, possibly as a result of pollen sterility.
Because Frondoso is a parent of Atlas 66 and quadrivalents were
observed to occur at a comparable frequency in both cultivars, it is
possible that Atlas 66 inherited its translocation from Frondoso.
Test crosses are being made to Frondoso to determine if quadrivalents
result from a translocation involving the same chromosome arms as in
Atlas 66.
References
Baier AC,
Zeller FJ and Fischbeck G (1974) Identification of three chromosomal
interchanges in common wheat, Triticum aestivum L. Can J Genet
Cytol 16: 349-354.
Burnham CR (1956) Chromosomal interchanges in plants. Bot Rev 22:
419-552.
Darlington CD and LaCour LF (1950) The handling of chromosomes. 2nd
ed., Alien and Unwin Pub. (London, UK).
Heyne EG (1958) Registration of improved wheat varieties, XXI. Agron
J 50: 396-399.
Kimber G and Sears ER (1968) Nomenclature for the description of
aneuploids in the Triticinae. Proc 3rd Int Wheat Genet Symp
(Canberra, Australia) pp 468-473.
Lange W, Linde-Laursen 1, Larsen J, Ljungberg A and Ellerstrom S
(1987) Cytogenetic analysis of structural rearrangements in three
varieties of common wheat, Triticum aestivum. Theor Appl Genet
73: 635-645.
Love RM (1951) Varietal differences in meiotic chromosome behavior of
Brazilian wheats. Agron J 43: 72-76.
Primard SJ, Morris R and Papa CM (1991) Cytogenetic studies on a
heterozygous reciprocal translocation in the wheat (Triticum
aestivum) cultivar Atlas 66. Genome 34: 313-316.
Suarez EY, Buck H, Garcia M and lerace G (1988) Pheno-karyotypic
instability in wheat. Proc 7th Int Wheat Genet Symp (Cambridge, UK)
PP 1185- 1193.
Vega C and Lacadena JR (1982) Cytogenetic structure of common wheat
cultivars from or introduced into Spain. Theor Appl Genet 61:
129-133.
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