(go to
KOMUGI Home) (go
to WIS List) (go
to NO.84 Contents)
Results
Production
The tetrageneric hybrid F1's were produced from crosses between
trigeneric hybrids and doubled diploids or amphidiploids by means of
in vitro culture of immature embryo. No high incompatibility was
observed. The results of tetrageneric hybrids crossed between
trigeneric hybrids (Triticale x Haynatriticum) and Agrotriticum, and
their embryo cultures are shown in Table 1.
Tetrageneric hybrid seeds were obtained easily, but most of the
endosperms were poorly developed or absent. After the embryos had
been rescued, ten and two tetrageneric hybrid plantlets were obtained
from two cross combinations. Meanwhile, there was a significant
difference in percentage of regenerated plantlets when Agrotriticums
in different ploidy were used as the male parent.
Morphology
Seedlings of the tetrageneric hybrid F1's were
transplanted to pots. Some hybrid plants were vigorous in vegetative
appearance. The average number of spikes per plant was 11, varying
from 4 to 23. All of the hybrid plants were immune to BYDV, powdery
mildew and rusts. The leaves of the hybrid seedlings were wide and
long, resembling those of common wheat. Their spikes varied widely in
morphology, showing some phenotypes that could not be found in their
parents. Some characters were peculiar to Haynaldia villosa,
such as the midrib bristles on outer glume (Fig.
1), fragile internode of rachis. For characters such as
resistance to BYDV, the hybrid plants were similar to their parents
of Agrotriticum. The hairy neck appeared in the hybrid plants is a
marked character to Secale cereale. The hybrid plants
maintained these special characters inherited from the four genera,
which were helpful to distinguish the true hybrids from the
false.
Fertility
The hybrids were infertile or low-fertile types. The tetrageneric
hybrids could produce seeds when selfed or backcrossed with wheat.
Seed setting percentage averaged 1.2% when self-crossed. Some plants
of hybrid F1 had no pollen or a few fertile pollens in the anther.
Only 0.5% of the pollens could be stained by the solution of
I2- KI in the cross combination of ((TS6xO x TH6xL) x
TA6xA2) (Table 2). However, its
seed setting rate was significantly improved when backcrossed with a
parent of Triticum species such as durum wheat, which could
reach at 36.6%.
Cytological examination on somatic cells
Observation on the somatic cells of tetrageneric hybrid
F1's showed that most plants had 39 chromosomes in the
cross combination of ((TS6xO x TH6xL) x TA6xA2) varied
from 37 to 40. The chromosome numbers were 47 and 50 in two plants of
((TS6x1330 x TH6xH) x TA8x16-3) (Table 2).
These materials and their derivatives are being analysed by using DNA
markers of their chromosomes and GISH methods (Tomita et al. 1993,
1994; Ma et al. 1994).
Derivatives of the tetrageneric hybrids
All selfed and backcrossed seeds were placed on moist filter paper at
room temperature. Most of the seeds did not germinate. The
F2 plants segregated obviously in morphology. The seeds
were similar to wheat in morphology. In F3 generation of
((TS6xO x TH6xL) x TA6xA2), 3 out of 15 seedlings were
chlorines. This character was inherited from the parent of
Agrotriticum. These seedlings died 40 days later after germination.
Twenty-one derivatives of F3 generation have been obtained
from the tetrageneric hybrids (Fig. 2). Some
plants were morphologically similar to wheat and had good fertility.
The seed set percentage was 32.7% on average, varying from 8.7% to
64.9%.
Discussion
Tetrageneric hybrids and their derivatives have been successfully
obtained by means of immature embryo rescue when Agrotriticum,
Haynatriticum and Triticale were used as bridge parents to overcome
the incompatibility and the infertility of direct crossing between
wild relative species of wheat. These materials are of particular
interest to demonstrate the genomic rearrangement during wide
crossing using molecular cytogenetic methods such as C-banding and in
situ hybridization. They can also be used as initial materials to
transfer multi-disease resistance into wheat through backcrossing and
chromosome engineering.
This study demonstrated that the male parents with different ploidy
can significantly affect the production of immature embryos and
regenerating ability of seedlings through embryo culture. When all
the parents used in ((TS6xO x TH6xL) x TA6xA2) were
hexaploids, the production of immature embryos reached at 10%,
obviously higher than that of 1.1% in ((TS6x1330 x TH6xH) x
TA8x16-3). The regenerating ability of seedlings through embryo
culture had similar result. Besides, reciprocal crosses, the parental
combination and culture media also had some effects on regenerating
ability of callus. For example, we found that hexaploid Triticale
often causes incompatibility of crosses or sterility of hybrid seeds
when used as a male parent.
The chromosomes of tetrageneric hybrids and their derivatives
originated from R, V, E andwheat genomes. These materials with the
same central genomes AA and BB can develop new types of multi-disease
resistance when self-crossed and backcrossed, such as multi-genera's
addition lines and multi-genera's translocation lines
(Fernandez-Escobar and Martin, 1988). So far, many selfed derivatives
have been obtained from the tetrageneric hybrids.
<--Back | -->Next
(go to
KOMUGI Home) (go
to WIS List) (go
to NO.84 Contents)