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Materials and methods
The experimental materials used in the study are described in
Table 1. Two inbred lines of rye and two
accessions of Ae. variabilis were used as male testers, and
CS was used as male control in the crosses. Spikes of CS and the two
amphiploids, CS/L.elongatum and CS/T. bessarabicum
(MuJeeb-Kazi and Hettel 1995) were emasculated and bagged to avoid
pollination with other plants. After 2-3 days, the stigmas of
emasculated florets were pollinated with fresh pollen of rye or
Ae. variabilis, then bagged again. The crosses were made
using two outermost florets of the middle spikelets in each spike in
the field condition. To evaluate the self-pollination seeds set
rates, the emasculated florets of CS and the two amphiploids were
pollinated with their fresh pollen respectively. Thirty days after
pollination, the number of florets with and without seeds were
recorded for each spike. The data are expressed as the percentage of
successful crosses over the total number of florets pollinated. CS
was used as control to detect the expression and suppression of the
recessive crossability genes of CS in amphiploids. The significance
of differences between the crossability percentages were detected by
Student's statistical t-test.
Results and discussion
The crossabilities of amphiploids CS /L. elongatum and CS
/T. bessarabicum with rye and Ae. variabilis
are compared with that of control, CS, in Table
2.
Crossability percentages of CS with Qinling rye and Jingzhou rye were
72.5% and 70.6% respectively, and were similar to the results
reported by Luo et al. (1992, 1993a, b). However, the crossabilities
of amphiploids CS/L. elongatum and CS/T. bessarabium
with rye were significantly lower than that of CS (Table
2). As seen in Table 2, crossability
percentages of CS/ L. elongatum with Qinling rye and Jingzhou
rye were 34.7% and 33.1%, and those of CS / T. bessarabicum
were 53.3% and 54.6%, respectively. There were two possible reasons
for explaining the lower crossability percentages between the two
amphiploids and rye. The one, the gamete fertility of the two
amphiploids may be lower than that of CS due to meiotic
chromosome pairing abnormalities. The other, there may be genetic
factors inhibiting the success of crosses of the two amphiploids and
rye. The self- pollination seed set rates of the amphiploids and the
crossability percentages of amphiploids with CS were similar to that
of CS (Table 2). This result indicated that
the gamete fertility of the two amphiploids were normal. Therefore,
the present experimental results could be explained that the
crossability of CS with rye was partly inhibited by a suppressor or
suppressors in the genomes of L. elongatum and T.
bessarabicum under amphiploid backgrounds. In fact, Liu et al.
(1998) had revealed that chromosome 4Ee of L. elongatum
suppressed crossability of wheat with rye by using chromosome
substitution or addition lines. However, the present results revealed
that suppressor(s) on the Eb genome of T.
bessarabicum also involved in the crossability of wheat with rye.
On the other hand, the average crossability percentages between
CS/L. elongatum and CS/T. bessarabicum with rye were
significantly different (t=4.55). This results also indicated that,
the suppressor(s) on Ee genome of L. elongatum was
(or were) stronger than that on Eb genome of T.
bessarabicum.
Similar results were also observed when amphiploids crossed with
Ae. variabilis. The crossability percentages of CS with
Ae. variabilis-1 and Ae. variabilis-2
were very high, and were 80.2% and 81.7% respectively. But the
two amphiploids had significantly lower crossability (Table
2). These results indicated that the crossability of CS with
Ae. variabilis was mostly inhibited by suppressor(s) on the
Ee genome of L. elongatum and the
Eb genome of T. bessarabicum in their
amphiploids.
A consistent difference in crossability percentages between
amphiploids crossed with rye and Ae. variabilis was also
observed. As seen in Table 2,
crossabilities of amphiploids with rye were 33.1-54.6%, but those of
amphiploids with Ae. variabilis were only 0-12.1%. The
average crossability percentages of amphiploids with rye was
significantly higher than that of amphiploids with Ae.
variabilis (t=13.65). This results indicated that the effect
of suppressor(s) inhibiting the success of crosses of amphiploids
with Ae. variabilis were stronger than that in the
crosses of the amphiploids with rye.
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