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In a similar study (Maan et al. 1999) crosses between a (Ae. longissima )durum line having a scs^t gene from T. timopheevi and a set of 14 double-ditelosomics of Langdon durum (LDN-dDts) produced dMt F₁'s with the expected meiotic chromosome number and pairing (2n=29; 13''+t1t''' ) and neither dMt F₁'s nor the progeny from crosses to normal durum produced PMC's with a multivalent configuration. Therefore, there was no chromosomal structural heterozygosity between LDN-dDts and durum Selection 56-1, while (vent) scs^spt;- durum had one or more translocation chromosomes.

The scs^t and scs^spt genes produced compatibility between the, nuclear genome of durum wheat and the cytoplasm of Ae. longissima (lo) or Ae. ventricosa (vent), respectively. Similarly, scs^ae in 1DL from common wheat produced compatibility with the (lo) and (vent) cytoplasms (Maan 1992b). Therefore, the scs^spt, scs^t, and scs^ae, genes are similar in regards to producing compatibility with the (vent) cytoplasm and the resulting durum lines are male sterile. From crosses with normal durum, the female gametes without scs^t or scs^ae were functional but produced shriveled seeds, while female gametes without scs^spt did not function. Either scs^spt on 2S produced nucleocytoplasmic compatibility as well as gametocidal activity or 2S has two genes; Gc and scs^spt

A common wheat line with a T2B.2S translocation chromosome has a gametocida1 gene in 2S from Ae. speltoides (Tsujimoto and Tsunewaki 1988) but the action of Gc in the alien cytoplasm has not been examined. Telosome 2S also has a scs^spt (Table 2) and female gametes without scs^spt did not function in the (vent) durum. Similarly, durum wheat and common wheat lines having chromosome 4SL from Ae. longissima or Ae. sharonesis have a Gc gene (Maan 1975, 1976), and a T4AL.4SL translocation chromosome, like 2BL.2S, has Gc as well as scs¹ genes that produce compatibility with the cytoplasm from the donor Aegilops species and gametes with T4AL.4SL are exclusively transmitted in the euplasmic as well as alloplasmic durum wheat lines (Maan unpub). The long arm of chromosome 1D (1DL) has a scs^ae gene in a T1AL.1DL or T1BS.1DL chromosome that produces compatibility between the nuclear genome of durum wheat and the Ae. longissima cytoplasm (Maan et al. 1999; Maan unpub). Similarly, a gene(s) in chromosome 1D from Ae. squarrosa produce distorted segregation favoring alien chromosome 1D over native chromosome 1D of common wheat (Dvorak pers comm), indicating, that the alien chromosome 1D had Gc-like activity. Thus, 2S from Ae. speltoids, 4SL from Ae. longissima, and 1D chromosomes from Ae. squarrosa have scs genes that are expressed differently in the different wheat genotypes. Alternatively, two genes, scs and Gc, are located in the three non-homoeologous chromosomes from three diploid species. In addition, certain chromosomes of other Aegilops species have Gc genes with different degrees of reduced Gc-like effects but their interactions with the alien cytoplasms have not been examined.

The action of the scs genes is cytoplasm specific. While Gc appears to be non-cytoplasm specific, even though Gc is more effective m certain alien cytoplasms than others; scs genes produce inter specific nucleocytoplasmic compatibility and female gametes having scs are functional, while female gametes without scs either do not function or when fertilized by male gametes of normal durum (not having scs) produce aborted seeds. Functionality of the male gametes, female gametes, and seeds without scs (or Gc) may represent different degrees of nucleocytoplasmic compatibility, and the female gametes function better because of the maternal effect(s) than male gametes.

According to the scs gene hypothesis (Maan 1995), different forms of native ancestral scs genes produce nucleocytoplasmic compatibility and fertility within species having differentiated nuclear and cytoplasmic genomes. The parental scs genes are expressed as sterility when hemizygous in the inter specific hybrids. Some of the alien scs genes, when experimentally transferred into the nuclear genomes of the tetraploid or hexaploid Triticum species (with or without the alien cytoplasms), also function as Gc genes that in certain inter specific combinations impair DNA repair mechanism and produce chromosomal breakage, numerical and structural chromosomal aberrations, including deletions, male and female sterility, self- or cross-incompatibility, exclusive preferential functioning of the male gametes and female gametes, differential survival of zygotes and/or seeds.

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