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Material and methods
Six wheat-Aegilops ovata hybrid lines derived from
the BC3F3-population of the Triticum
aestivum Chinese Spring x Aegilops ovata amphiploid
(Ganeva et al. 1992) were studied. Both parents were also included.
The excess Cu tolerance was assessed at seedling stage at two
concentrations of Cu ions in CuSO4 solution
(CuSO4.8H2O): 10-6 M and
10-5 M. Plant growth was estimated by measuring the length
and fresh weight of roots, shoots and the whole plant. To measure
tolerance the tolerance index (TI) was calculated as a ratio: growth
in metal solution / growth in control solution (water) (Macnair
1993). Chromosome counts and arm ratio measurements were made in root
tip cells on N-banded chromosome spreads. N-banding was conducted
according to Gill et al. (1991).
Results and discussion
The roots length reduction in Aegilops ovata was
significantly less than in Chinese Spring at both low and high Cu
concentrations (Fig.
1). There was no
significant difference between the two parental genotypes regarding
the shoots growth at concentration of 10-6 M. At the
higher concentration the performance of Chinese Spring was
better.
The performance of two of lines, ADL-18 and ADL-33, was better at
both concentrations of Cu ions in comparison with the, parents and
the rest of lines. They combined the better roots growth of the wild
species with the better shoots growth of 'Chinese Spring' at stress
conditions (Fig.
1).
The chromosome N-banding analysis showed that both tolerant lines,
ADL-18 (2n=40+4t) and ADL-33 (2n=40+3t) carry one and the same pair
of submetacentric (arm ratio 2.45) Aegilops ovata chromosomes
substituted for wheat D-genome chromosomes (Fig.
2). The N-banded
karyotype of the parental Aegilops ovata accession is given
for comparison (Fig.
3). The rest of
lines do not carry this alien chromosome. The telocentrics are
supposed to be the short and the long arm of wheat chromosome 4A,
which is missing in the complement of both lines. The comparison with
the C-banded (Friebe et al. 1995) and N-banded (our unpublished
results) chromosomes of the U- genome donor, Aegilops
umbellulata, suggests that the alien chromosome pair is 3U
(Fig.
3). Studies on
the genetical control of mineral stress tolerance indicated the major
effect of homoeologous groups 5 and 2 chromosomes in the members of
Triticeae (Manyowa and Miller 1991). The role of group 3 chromosomes
has also been reported. Aluminum tolerance has been transferred into
bread wheat through chromosome 3N of Aegilops uniaristata
(Miller et al. 1992). Modifying genes for excess boron tolerance were
found on chromosome 3R in rye, 3S in Aegilops sharonensis and
3E in Agropyron elongatum (Manyowa 1989, cited in Manyowa and
Miller 1991). We suppose that the Aegilops ovata chromosome 3U
contribute to the excess Cu tolerance through its effect on the
growth of roots. In wheat, the effect of group 3 chromosomes on root
development has been established (Sears .1954). Both ADL-18 and
ADL-33 lines had slower root growth in control solution compared with
the rest of lines and the parents (data not shown). This opinion is
also in agreement with the observation that in most cases tolerant
ecotypes have slower growth than the typical non-tolerant ones
(Macnair 1993).
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