Introduction
Wide hybridization was accomplished by crossing durum wheat,
Triticum turgidum L var.durum cv. 'Nodak'
(2n=4x=28) with intermediate wheatgrass, Agropyron
intermedium (Host) P.B.
[Thinopyrum intermedium (Hoot) Barkworth and
Dewey] (2n=6x=42) (Smith, 1942). The hybrid doubled naturally by
unreduced gametes and was received as a partial amphiploid with
chromosome numbers of 2n=58-74 (Schulz-Schaeffer 1970). Selection for
chromosome stability was carried out over several generations. An
x-ray irradiated octoploid derivative of this partial amphiploid was
released in 1987 as MT-2 (Schulz-Schaeffer and H 1987). It was
characterized by Giemsa-C-banding (Schulz-Schaeffer and Friebe 1992).
MT-2 was backcrossed to durum wheat (cv. Wells, C.I. 13333)
(Schulz-Schaeffer and McNeal 1977) and selfed for 6 generations after
backcrossing. Selfing resulted in the elimination of someAgropyron
univalents and in others becoming bivalents (Schulz-Schaeffer and
Haller 1988). This material was released as MT-4
(Schulz-Schaeffer 1989). MT-4 had 2n=32-44 chromosomes,
accounting for 16-21 bivalents and 0-9 univalents (Avg.18.5 I + 3.5
II). This wide variation in total chromosome number and in
degree of chromosome pairing originated from the following breeding
approach. After backcrossing MT-2 to durum wheat, all Agropyron
chromosomes were univalents. In subsequent selfing generations
only some chromosomes reestablished pairing relationships, others
stayed unpaired, and some were eliminated. Meiotic stabilization of
MT-4 by continued selfing, selection for plants with 7
Agropyron chromosome pairs, and selection by
single-seed-descent breeding (Brim 1966) was accomplished. The result
was a stable line MT-4-1-1. The purpose of this paper is to
characterize the chromosome constitution of MT-4-1-1 by
Leishman-C-banding analysis which will allow more directed chromosome
engineering of this material.
Materials and Methods
Seeds of MT-4-1-1 were placed on moist blotter paper for
germination at 23oC. Root tips at lengths of 1.5 to 2.5 cm
were collected and pretreated at WC for 24 hrs. Root tips were
further pretreated in O0C 45% acetic acid and after excising of the
root cap, the meristematic tissue was squeezed out of the epidermal
tube. After squashing in 45% acetic acid, the preparations were
checked under phase contrast. Cover glasses were frozen on dry ice
for 5 minutes and removed with a razor blade. Slides were immediately
placed into 99% ethanol for overnight. Leishman-C-banding was carried
out according to the method by Gill et al. (1991) except that liquid
BDH Wright's Leishman stain (eosin methylene blue, 0.2% w/v solution
in methanol) was used instead of Giemsa stain.