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Results and
discussion
Pollination of 143 emasculated Chinese Spring florets by
D.
villosum
yielded 1 seed, a ca. 0.7%
seed set in 1993,
whereas of 102 florets pollinated, 3 seeds were obtained, seed set
was 2.9% in 1994. The t-test indicates there is no significant
difference in two years, which inferred the crossing rates were
identical in this study.
The results of cross were listed in Table
1, including the
pollinated florets and percentages of seed set. The percentage of
seed set varies between 0.0% and 22.6%. With regard to the female
parents of monosomics, two distinct classes were found when
D. villosum
was used as pollinator. In the combinations with homoeologous
group 5 of monosomics (5A, 5B and 5D) 17.1%,
22.6% and 10.8% of
seed set were obtained, which demonstrated significantly higher seed
set than that in cross with normal Chinese Spring by t-test, whereas
in those with other homoeologous groups of monosomics, the
percentages of seed set were below 10%, which did not exhibit
remarkable differences in comparison to that with normal Chinese
Spring. These results suggested the import ant role of maternal
genotypes in wheat-D. villosum hybridization. We have known
that three kr genes, which located on chromosomes 5A, 5B and
5D, respectively, control crossability between Chinese Spring wheat
and rye species. The crossabilities of Chinese Spring with other wild
species controlled by the kr genes have been reported in
Elymus giganteus (Mujeeb-Kazi et al. 1983), Hordeum vulgare
(Fedak and Jui 1982), and Hordeum bulbosum (Falk and Kasha
1981). Dai et al. (1988) investigated the relationship between the
crossability of common wheat cultivars with D. villosum and
rye, Secale cereale, by using common wheat cultivars having
high and low crossable rates with rye, and found that the
crossabilities of common wheat cultivars with D. villosum and
rye are controlled by the same genetic system. Koba and Shimada
(1998) reported the similar result using Aegilops squarrosa
and Secale cereale. These findings support the traditional
concept that the crossability between Chinese Spring wheat with wild
species was suppressed by Kr genes, while was promoted by the
recessive loci. Halloran (1966) reported a 1.2% seed set in his work
using the monosomic 5B of Chinese Spring as female parent crossed
with D.
villosum,
while using Chinese Spring as female parent, no seed was
obtained. He has suggested that there might be a gene(s) on
chromosome 5B of Chinese Spring which prevented successful cross in
disomic condition, but in monosomic state, was ineffective. In the
present study, it was found a high percentage of seed set in the
cross between monosomic lines of 5A, 5B and 5D and D.
villosum. With the results in the present study, we suggested
that the three pairs of kr genes for crossability would be the
recessive mutants of Kr gene, which expressed as reducing the
effect on preventing cross between wheat and its wild species.
Different kr gene would exhibit different degree of effect an
reducing to prevent wide cross. The kr1 gene is the strongest
mutant to reduce the effect of preventing wide cross and kr3
is the weakest one. The results would have demonstrated the dosage
effect of hr genes on preventing wide cross. The lack of kr
genes in monosomics resulted in a higher seed set in their
crosses with D. villosum.
Many obtained hybrid seeds failed to germinate on moist paper in
petri dishes in the laboratory due mainly to their extremely
shrivelling endosperm. Chen et al. (1982) and Dai et al. (1988) found
that the percentages of wed set in crossing T. tauschii as
female parent, with D. villosum were considerably high (up to
80%), but the hybrid seeds almost did not germinate due to the lack
of endosperm. T.
tauschii is the donor species of D genome in hexaploid
wheat. These facts may provide an evidence that a gene(s), carried on
a certain D genome chromosome in T. tauschii and hexaploid
wheat, refrains from development of endosperm in the process of seed
formation after hybridization.
Table
1 shows the
seedling frequencies per 100 florets pollinated is relatively low.
For obtaining more hybrid plants, it is necessary to employ the
cultural embryo rescue technique in the cross as von Bothmer and
Claesson (1990) did in their work.
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