Materials and methods
A (vent ) durum line having a T2BL.2S translocation chromosome consisting of long arm of chromosome 2B (2BL) of durum and the short arm of chromosome 2S (2S) of Ae. speltoides, a (lo) 28-chromosome durum line having scsti from T. timopheevi, and (un ) 29chromosomes having a un telo were available at North Dakota State University, Fargo, ND. These lines were used as female parents. The 1D(1A) and 1D(1B) disomic-substitution (DS) lines of Langdon durum were available from Joppa (1988).
The(vent ) 28-chromosome T2BL.2S/2B durum, (lo) 28-chromosome scsti durum, and (un ) 29chromosome (2n=29, 14"+t' (un-telo)) durum lines were crossed to the 1D(1A) and 1D(1B) DS lines of Langdon durum (LDN). The resulting 1D+ 1A and 1D+1B double-monosomic (dM) F1s were backcrossed to the corresponding LDN DS lines as the recurrent male parents. The resulting 1D(1A) and 1D(1B) DS lines of LDN durum were maintained by crossing to the corresponding LDN DS lines. The crossed spikes of the alloplasmic 1D(1A) and 1D(1B) DS lines were examined for seed-set. The individual plants of the hybrid progeny were examined for meiotic chromosome number and meiotic chromosome pairing at metaphase I of meiosis in the pollen mother cells (PMC).
Results and Discussion
The backcrosses of (lo) or (un) durum lines to the LDN 1D(1A) and 1D(1B)DS lines as recurrent male parents produced (lo) or (un) 1D(1A) and 1D(1B) DS lines that were male sterile. They had complete seed-set in the crossed spikes, 14 closed pairs (13 pairs of durum chromosomes and 1 pair of 1D chromosomes) in the PMCs and were maintained by crossing to the corresponding LDN DS lines. Apparently, the scsae on chromosome 1D substituted for scsti in the (lo) scsti durum, and for scsun in the (un) scsun durum lines (Table 1).
The backcrosses of (vent) scsspt durum having T2BL.2S translocation chromosome to the LDN 1D(1A) and 1D(1B)DS lines as recurrent male parents also produced male sterile (vent) 1D(1A) and 1D(1B) DS lines that were maintained by crossing to the corresponding LDN 1D(1A) or 1D(1B) DS lines (Table 1). However, compared to (lo) or (un) DS lines, the (vent) DS lines produced only about 50% of the seed set in the crossed spikes.
The meiotic chromosome pairing in the PMCs of plants in the (vent) 1D(1A) and (vent) 1D(1B) DS lines showed that they had 13 closed chromosome pairs and 1 open pair, indicating that the female gametes with T2BL.2S were exclusively transmitted and gametes without this chromosome did not function. However, scsspt did not produce translocations in the presence of scsae on chromosome 1D, even though the scsspt produced chromosomal structural alterations indicated by one or more multivalent configurations in the PMCs of certain plants of the (vent) scsspt durum line (Maan and Kianian 2001). The (vent) 1D(1A) and (vent) 1D(1B) DS lines having scsspt were partially female fertile and produced 50% seed set in the crossed spikes relative to un or lo crosses.
The results indicated that (vent) durum havingT2BL.2S translocation chromosome with 2S from Ae. speltoides produced functional female gametes having T2BL.2S and those without this chromosome did not function. The T2BL.2S chromosome remained fixed in the (vent) 1D(1A) and 1D(1B) DS lines but did not produce chromosomal abnormalities. Possibly, the expression of scsspt was altered in the presence of scsaescsae gene in chromosome 1D pair of the (vent) 1D(1A) and (vent) 1D(1B) DS lines of LDN durum.