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Materials and methods
Nine cultivars viz., Jauhar, M-143, Pavon, Sindh-81, Sarsabz,
Mexipak, Sonalika, ZA-77 and Chinese Spring of Triticum
aestivum L. (2n = 6x = 42; AABBDD) were used in the present
study. Chinese Spring was included as a check cultivar to make
meaningful comparisons.
Seeds were germinated in the petri dishes, lined with moist filter
paper, and kept in the dark at room temperature for about 72 hours.
Root tips were harvested and transferred to another petri dish for
the pretreatment, also kept in dark for 2.5 hours as described by
Jahan and Vahidy (1989). The pretreatment solution used was a mixture
of 10 mg colchicine, 5 mg 8-Hydroxy-quinoline and 5 drops of DMSO in
20 ml of distilled water. The root tips were fixed in 0.2%
acetocarmine and stored for two days in the refrigerator at 4C. The
use of 0.2% acetocarmine helped in getting good spread of the
chromosomes for N-banding. The cover glasses were removed by liquid
nitrogen before further processing. The slides were treated for 10-15
minutes in 45% acetic acid at 60C, air-dried and kept at room
temperature for 2-3 days. Treatment of the slides in 2M phosphate
buffer was similar to that descrided by Jahan et al. (1990). Slides
were then washed 3-4 times in deionized water and stained in a liquid
Giemsa solution, using 10 ml of prepared Giemsa (Fluka No. 48900) in
195 ml of 1/15 M Sorenson's phosphate buffer at pH 6.8 for about 45
minutes at room temperature. The slides were rinsed briefly in 1/15 M
Sorenson buffer, air-dried for 2-3 days and mounted in the Canada
balsam. From permanent slides at least five cells were selected for
photomicrography and karyotyping. The identification of chromosomes
was based upon diagnostic banding patterns as elucidated by Endo and
Gill (1984) and Gill et al. (1991).
Results and discussion
Sixteen out of twenty one chromosomes exhibited distinct
N-banding patterns. No bands were observed in chromosomes 1A, 3D, 4D,
5D and 6D. N-banding polymorphism was observed mainly in the B-genome
chromosomes in all cultivars. The chromosomes 3A, 1B, 5B, 1D and 7D
exhibited maximum banding pattern consistency. The overall banding
pattern among cultivars was similar to that of Chinese Spring, though
some differences described in Table
1 were
observed.
The chromosome 2A consistently had faint proximal 2AL1.3 and terminal
2AL1.5 bands in the long arm and a prominent proximal 2AS1.3 band in
the short arm. The chromosomes 2A and 3A can often be confused with
each other and could be misidentified as both have a similar sized
bands in the proximal region of the short arm (Endo and Gill 1984).
The terminal band 2AL1.5 of Chinese Spring was not observed in
Jauhar, Sindh-81 and Sarsabz cultivars. Proximal band 4AL1.3 was not
observed in Jauhar, M-143, Pavon and Sarsabz. The terminal band
4AL2.7 was not observed in any cultivar except Sonalika and Chinese
Spring (Table
1). The proximal
band 5AL1.3 was darker in M-143 as compared to the other
cultivars.
A reciprocal translocation was observed in M-143 cultivar. Instead of
normal 5A and 4B chromosomes 5AL/4BL and 5AS/4BS translocated
chromosomes were observed (Fig.
1). Gill and
Kimber (1977) observed a translocation in 4A (later renamed as 4B)
and the 6B chromosomes of cultivar Thatcher. The characteristic twin
bands, 6AL1.3 and 6AL1.5 were not observed in Pavon and Sindh-81
(Table
1). Endo and Gill
(1984) also did not observe these bands in pure lines and
substitution lines of four wheat cultivars. The terminal band 7AS1.5
was missing in Sarsabz and ZA-77, while the terminal band 7AL1.7 was
not observed in Jauhar.
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