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Wheat-barley recombinant chromosomes involving barley chromosome arms
3HL or 6HL have been produced by Islam and Shepherd (1992a). In their
procedure, wheat plants which were double monosomic for 5B and either
3A or 6A were pollinated with the corresponding ditelosomic
wheat-barley substitution lines, i.e., 3HL(3A) or 6HL(6A) (Islam and
Shepherd 1992b), and plants with 19"+5B'+t'3HL or t'6HL were selected
cytologically. To induce homoeologous recombination, these plants
were further crossed with Sears' ph1b mutant, and triple
monosomic stocks, i.e., 19"+5B'ph1b+t'3HL+3A'or
19"+5B'ph1b+t'6HL+6A', were selected. Wheat-barley recombinant
chromosomes were isolated from the selfed progeny using isozyme
markers to screen for dissociation of the barley markers.
The major problem for producing wheat-alien recombinants is the
expected low pairing frequency between wheat and alien chromosomes.
Islam and Shepherd ( 1988, 1992a) reported that barley chromosomes
paired with frequencies of 0.3% and 2.6% in the triple monosomic
stocks, 19"+5B'ph1b+t'3HL+3A' and 19"+5B'ph1b+t'6HL
+6A', respectively. Koebner and Shepherd (1986) have utilized both
the phlb mutant and 5B nullisomy to induce homoeologous
recombination between wheat and rye chromosomes. They obtained a
higher level of homoeologous pairing (three-fold increase of
recombination rate) between wheat and rye chromosomes by using 5B
nullisomy rather than using the ph1b mutant. This finding
suggests that 5B nullisomy may induce increased pairing between wheat
and barley homoeologous chromosomes.
Because of the expected low pairing frequency between wheat and
barley chromosomes, an effective selection system for identifying
recombinants is necessary. Isozyme markers,which were used by Islam
and Shepherd (1992a), are not widely applicable for identification of
recombinants because the number of markers is limited. Numerous
molecular markers detecting polymorphism between wheat and alien
species have been developed in the past few years. For example, Blake
et al. (1996) developed 135 barley chromosome-specific STS-PCR
markers, 19 of which are 5H- specific. The selection efficiency is
expected to be greatly enhanced by the use of these STS-PCR
markers.
References
Blake TK, Kadyrzhanova D, Shepherd KW, Islam AKMR, Langridge PL,
McDonald CL, Erpelding J, Larson S, Blake NK and Talbert LE ( 1996)
STS-PCR markers appropriate for wheat-barley introgression. Theor
Appl Genet 93: 826- 832.
Islam AKMR and Shepherd KW (1988) Induced pairing between wheat and
barley chromosomes. Proc 7th Int Wheat Genet Symp, Cambridge,
309-314.
Islam AKMR and Shepherd KW (1992a) Production of wheat-barley
recombinant chromosomes through induced homoeologous pairing. 1.
Isolation of recombinants involving barley arms 3HL and 6HL. Theor
Appl Genet 83: 489-494.
Islam AKMR and Shepherd KW (1992b) Substituting ability of individual
barley chromosomes for wheat chromosomes. 1. Substitutions involving
barley chromosomes 1, 3 and 6. Plant Breed 109: 141-150.
Islam AKMR, Shepherd KW and Sparrow DHB (1981) Isolation and
characterization of euplasmic wheatbarley chromosome addition lines.
Heredity 46: 161-174.
Koba T, Takumi S and Shimada T (1997) Isolation, identification and
characterization of disomic and translocated barley chromosome
addition lines of common wheat. Euphytica (in press)
Koebner RMD and Shepherd KW (1986) Controlled introgression to wheat
of genes from rye chromosome arm IRS by induction of allosyndesis. 1.
Isolation of recombinants. Theor Appl Genet 73: 197-208.
Murai K (1995) Development of barley chromosome-specific RAPD markers
for identification of barley chromosomes added to the wheat genome.
Bull RIAR, lshikawa Agr Coll 4: 31-37.
Murai K, Koba T and Shimada T (1997) Effects of barley chromosome on
heading characters in wheat-barley chromosome addition lines.
Euphytica (in press)
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