Molecular cytogenetic characterization of an alloplasmic durum wheat line with a portion of chromosome 1D of Triticum aestivum carrying the scsae gene

Triticum aestivum (2n = 6x = 42, AABBDD) with Triticum longissimum (2n = 2x = 14; S'S) cytoplasm ((lo) cytoplasm) has normal fertility and plant vigor. However, the nucleus of durum wheat (Triticum turgidum (2n 4x = 28, AABB)) is incompatible with the T longissimum cytoplasm, producing non-viable progeny. This incompatibility is alleviated by scs(ae), a species cytoplasm-specific (scs) gene, on the long arm of chromosome 1D (1DL) of common wheat. The hemizygous (lo) durum scs(ae) line is male sterile and is maintained by crossing to normal durum wheat. After pollination, the seeds produced are either plump and viable (with scs(ae)) or shriveled and inviable (without scs(ae)). Thus, the chromosome with scs(ae) is inherited as a whole without recombination. The objectives of this study were to characterize the chromosome carrying scs(ae) and to determine the process through which this gene was introgressed into the (lo) durum background. Molecular marker analysis with 27 probes and primers mapped to homoeologous group 1 and genomic in situ hybridization using differentially labeled total genomic DNA of durum wheat and Aegilops tauschii suggest the presence of a 1AL segment in place of the distal region of 1DL. Owing to the. absence of any detectable duplications or deletions, homoeologous recombination is the most likely mechanism by which this introgression occurred.