The scs^t gene is closely linked with the centromere on the long-arm of chromosome 1A (1AL) (Anderson and Maan 1995; Maan et al. 1999). A scs^t gene with an effect similar to the one on 1AL is also located on the long-arm of chromosome 1D (1DL telo) from common wheat and a telocentric chromosome from Ae. uniaristata [(un) telo] (Maan 1994, 1995). The 29-chromosome durum plants having an alien telo and (lo) or (un) cytoplasm are male sterile and when crossed to the normal durum produce about 15% plump and viable seeds having the alien telo, while the seeds having euploid embryos are shriveled and inviable. These results show that the alien telocentrics also have a scs^t gene that improves compatibility with the (lo) or (un) cytoplasm and the resulting 29-chromosome plants are male sterile (Maan 1992a, b).

A dominantly inherited vitality (Vi) gene located on the short-arm of chromosome 1B (1BS) has a positive xenia effect on seed plumpness and seed viability, and produces male fertility in the (lo) or (un) durum male-sterile lines having scs^t (Anderson and Maan 1995; Maan 1992a, b). The (lo) or (un) durum plants having scs^tscs^t and ViVi gene pairs produce true breeding fertile progeny and when crossed as a male to the (lo) or (un) scs male- sterile durum lines produce plump-viable seeds and fertile plants with the scs^t and Vi genes (Anderson and Maan 1995; Maan 1992b). However, the affects of scs^t or Vi in the cytoplasmic background of the normal durum wheat have not been reported.

Our objectives were (1) to transfer the scs^t gene from a (lo) durum line to the cytoplasmic background of normal durum wheat, (2) to determine the fertility of the euplasmic durum with a scs^tscs^t gene pair, and (3) to use euplasmic durum line having a scs^t/scs^t gene pair (if fertile) as a recurrent male parent to propagate a (lo) male-sterile durum line.


Materials and methods

The breeding behavior of the genetic stocks used in this study are described below; (1) The (lo) durum line carrying one copy of the scs^t gene is maintained by crossing as the female to control durum. The scs^t gene is maternally transmitted through the plump and viable seeds, while the seeds without scs^t are shriveled and inviable (Maan 1992a, b, 1994, 1995). (2) A true breeding fertile durum line has (lo) cytoplasm and scs^tscs^t and ViVi gene pairs (Anderson and Maan 1995). (3) A 1D (1A) disomic-substitution line of Langdon durum (Jappa 1988) (Note: Langdon double-ditelosomic can also be used, because chromosome 1A with scs^t is exclusively transmitted through heterosexual gametes). (4) The control durum selection 56-1.

We crossed a 1D(1A )disomic-substitution line of Langdon durum as a female parent to the fertile durum line having (lo) cytoplasm and scs^tscs^t and ViVi gene pairs (Fig. 1). The 1A+1D double-monosomic F₁'s were partially fertile. The F₂ individuals were cytologically examined. All disomic F₂ individuals were expected to carry a paternal 1A chromosome pair with scs^tscs^t, while others may or may not have Vi. An F₂ plant with scs^tscs^t (but without Vi) was selected by testcrossing to the (lo) male-sterile line. The F₂-derived progeny was used as a recurrent male parent to maintain male-sterile durum line having (lo) cytoplasm.