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Among, the six chromosome
substitution lines, all of the lines showed significant reduction in
their crossabilities with Ae. squarrosa from that of Chinese
Spring under field condition at the 5% or 1 % levels. Chromosome 5B's
of both Hope and Cheyenne showed the greatest reduction among the
homoeologous chromosomes. Chromosome 5D's also induced lower
crossabilities than those of chromosome 5A's of Hope and Cheyenne,
although no significant differences were observed among the six
substitution lines after t-tests. These facts show that
genetic factors controlling the crossability of wheat with Ae.
squarrosa locate on all of the homoeologous group 5
chromosomes.
As to the crossabilities with rye, chromosome 5B's of Hope and
Cheyenne showed greater reduction than chromosome 5A's which also
showed significant differences from Chinese Spring. Chromosome 5D's
of Hope and Cheyenne did not show any reduction in the crossability
with rye as reported in the previous works (Snape et al. 1979, Falk
and Kasha 1983), instead, 5D of Cheyenne showed higher crossability
than that of Chinese Spring. The inefficiency of chromosome 5D's of
Hope and Cheyenne on the reduction of the crossability of common
wheat with rye was different from their responses with Ae.
squarrosa.
Discussion
Genetic analyses on the crossabilities of common wheat with alein
species have been done with respect to those with rye, Secale
cereale (Lein 1943, Riley and Chapman 1967) and Hordeum
bulbosum (Snape et al. 1979, Falk and Kasha 1981,1983, Sitch and
Snape 1989). In both cases, Kr1 and Kr2 alleles,
located on chromosomes 5B and 5A, respectively, were shown to have
major roles on the crossability of wheat. However, since Krowlow
(1970) reported that chromosome 5D carried crossability gene Kr3,
it has not been clearly shown that chromosome 5D had any effects
on the crossabilities with rye or H. bulbosum, except that
Fedak and Jui (1982) showed all of the homocologous group 5
chromosomes, including 5D, had responsibility for the crossability of
wheat with a cultivated barley Betzes, although they used wheat lines
as male parents. In the present study, it was demonstrated that not
only chromosomes 5B and 5A, but also chromosome 5D had responsibility
in the crossability of wheat with Ae. squarrosa. Therefore, it
is probable that the genetic factors controlling the crossability
with Ae. squarrosa located on the chromosomes 5A, 5B and 5D
correspond to Kr2, Kr1 and Kr3,
respectively.
Since Ae. squarrosa is the D genome donor of common wheat, it
seems strange that the crossability of common wheat
with Ae. squarrosa is suppressed by the genetic factor(s)
located on the chromosome of the D genome itself. Riley and Chapman
(1967) described the evolutional significance of the Kr1 and
Kr2 alleles with respect to the relationship between wheat and
rye that the dominant inhibitors of crossability arose by mutation
and conferred evolutional and agricultural advantage upon wheat by
preventing the production of sterile wheat-rye hybrids. Probably as
in the case of Kr1and Kr2, dominant mutation would be
occurred at a locus on chromosome 513 after the establishment of
hexaploid wheat by hybridization between tetraploid wheat and Ae.
squarrosa. Variation in the crossabilities of common wheat
cultivars with Ae. squarrosa may be due to the combinations of
the dominant cross inhibiting factors located on the homoeologous
group 5 chromosomes.
Since the genetic factor(s) located on chromosome 5D was found to be
effective only for the inhibition of hybridization with Ae.
squarrosa, not with rye, the factor(s) might be specific to
prevent the production of wheat -Ae. squarrosa hybrid. More
precise genetic characterization of the factors on the crossability
with Ae. squarrosa will be necessary.
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