Chromosome morphology
The mean arm-ratio values for most chromosomes (data not shown) in
all morphotypes were similar to those of SC, and lay within the range
reported previously for tetraploid wheats (Langdeva et al. 1995) and
the AB genome chromosomes of hexaploid wheat (Endo and Gill 1984).
However, 7B (within median type) showed varying arm- ratio values
ranging from 1.14 in B-3-11 and A-1-116 to 1.57 in DZ-04-118 and
B-3-33. Compared to 7B of SC, only the mean arm ratio values of B3-11
and A-1-116 (no chromosomal rearrangement was expected) were
significantly different (Table 1).
C-banding
For all chromosomes, within-genotype C-band polymorphism was almost
absent. The possibility that differences in banding procedures could
account for the variation was ruled out since we have recovered
almost all the landmark bands for the AB-genome chromosomes of
Chinese Spring (Gill et al. 1991) in at least one landrace
morphotype. Furthermore, the banding patterns of SC were nearly the
same as that reported by Simeone et al. (1988) who used a different
technique.
C-banded chromosomes of each landrace morphotype, together with
SC, are depicted in Fig. 1 and Fig.
2. C-banding polymorphism was observed for all chromosomes with
possible exceptions of 1A and 4A. For each chromosome, polymorphism
was mostly due to the presence/absence of bands and differing band
positions. Satellite regions of chromosomes 1B and 6B also showed
variation. Within the landraces, no two morphotypes were identical
for all chromosomes, including those from the same population (B-3-11
and B-3-33). In addition, C-band polymorphism was not associated with
spike morphology. The notable findings from the present study are
summarized as follows:, (1) None of the morphotypes showed a similar
C-banding pattern to SC for chromosome arms 3BL, 5AL and 5BL, (2)
Banding patterns not included in the polymorphic types of the AB
genomes of hexaploid wheat varieties (Friebe and Gill 1994) were
observed on chromosomes 2AS, 6AL, 7A, 3BL, 5BL, 7BS and, possibly,
1B. (3) Compared to previous other studies, the prominent band near
the proximal region of 2AS in K-1-1, B-3-33 and DZ-04-118 (less
clear) and, the band positions on 7AL and 5BL in B-3-33 were unusual.
Only B-3-11 showed three band positions on 5BL, but this was
previously observed in one other landrace morphotype (Belay and
Merker 1998). (4) Chromosome 7B of B-3-11, which was easily confused
with 4B, was conspicuously different from the others because the
interstitial bands on the short arm were absent and band 7BL2.5 was
rarely observed (Fig. 3). Further, 7A of
this morphotype was rather similar to 7At of T.
timopheevi Zhuk. (Badaeva, Filatenko et al. 1994), although the
interstitial band on 7AS was previously observed in the wild
tetraploid wheat progenitor, T. dicoccoides Korn. by
N-banding (Landgeva et al. 1995).
Detection of translocation breakpoints
Generally, the chances of localizing translocation breakpoints by
C-banding alone proved difficult, presumably because of the lack of
enough bands accompanied by conserved centromeric positions. However,
DZ-04-118 might have carried a 2B/4B translocation with the
breakpoints located in the distal regions of 2BS and 4BS (Fig.
2). This was considered equivocal because similar bands were
observed on 4BS of A-1-116, which was not expected to carry a
translocation. That means, if the subtelomeric bands on 4BS are
variant forms, then 2BS in DZ-04-118 may be carrying a terminal
deletion.
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