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Results

1. Gc gene from Ae. longissima: Chromosomes of the original alloplasmic line, C20, were observed. Three and six of the plants carried 43 and 44 meta or submetacentric chromosomes, respectively. A pair of extra chromosomes was included in all the plants, whose C-banding pattern was similar to that of chromosome 5S1 of Ae. longissima (Friebe 1993, Fig.1a).

Both the plants with 43 and 44 chromosomes were self-pollinated or crossed as males to normal CS, and the karyotypes of the progenies were observed (Table 1). Most of the selfed progeny possessed 44 normal chromosomes, whereas many of the crossed progenies contained broken chromosomes, though the mode of the chromosome numbers was 43. The selfed and crossed progenies had respectively a pair of chromosomes and one chromosome similar to 5S1. This result indicates that this alien chromosome carried a Gc gene and, therefore, was preferentially transmitted to the next generation. The chromosome carrying Gc gene was heterobrachial as seen in root tip mitoses, and formed a univalent with a satellite in the backcrossed plants (Fig. 2a). Some of the plants carried one or two multivalents that must have been products of translocated chromosomes caused by this Gc gene (Fig. 2b). The seed fertility of the crossed plants was very low (10.3 % plus or minus SE 1.3), indicating that the original cytoplasmic substitution line, C20, carried a pair of Ae. longissima chromosomes possessing a Gc gene.

2. Gc gene from Ae. sharonensis: The original amphidiploid between T. dicoccum and Ae. sharonensis (genome AABBS1S1) was crossed with CS. The F1 was recurrently backcrossed with CS. In the BC4F1 generation, 1 noticed segregation of the stem color at three red and three white. Each plant with red or white stems was separately backcrossed with CS. In the next generation (BC5F1), all the progenies from BC4F1's with white stems (cross 1) had white stems, whereas progenies of plants with red stems (cross 2) segregated at three red and six white. Meiotic configuration of plants with red and white stems from these crosses indicated that all the plants from cross 1 carried one extra chromosome only (Fig. 2c), whereas all red and some white plants from cross 2 contained other alien or translocated chromosome(s) with an alien chromosome segment (Fig. 2d). The C-banding pattern of the alien chromosome that was transmitted preferentially, regardless of the stem color, was similar to that of chromosome 4S1 of Ae. longissima (Friebe et al. 1993, Fig. 1b). In plants with 41 or 42 chromosomes, this alien chromosome was substituted for chromosome 4B of common wheat (instead of 4D). Therefore, this chromosome is 4S1 of Ae. sharonensis.


Discussion

There are two types of gametocidal chromosomes in Ae. longissima and Ae. sharonensis (Endo 1985). One belongs to homoeologous group 2 and another 4 of wheat. The Gc genes on group-4 chromosomes are epistatic to the ones on group-2 chromosomes (Endo 1982). There are no reports, so far, that any Gc gene is located on group-5 chromosomes. However, the C-banding pattern, heterobrachial shape. and satellite in the univalent of the present Ae. longissima chromosome are the characteristics of chromosome 5S1 (Friebe et al. 1993). There is no evidence, however. that this alien chromosome is substitutable for group-5 chromosomes of wheat or that it carries genetic markers for group-5 chromosomes. Thus, this chromosome is most probably chromosome 5S1, but it remains a possibility that it is a product of a complicated translocation involving the chromosome 2S1 or 4S1

The Gc gene of the present Ae. sharonensis strain was located on chromosome 4S1. Maan (1975), Endo (1981), and Miller et al. (1982) also reported Gc genes on either chromosome 2S1 or 4S1 of this species. In the course of this study I found that the Ae. sharonensis strain KU5-1 used for the present amphidiploid (AABBS1S1) was the same as the strain for the alloplasmic line from which Endo (1981) had identified his Gc gene. However, Endo's chromosome was 2S1 though the present chromosome was 4S1. Obviously, the Ae. sharonensis strain KU5-1 carries at least two gametocidal genes, one on chromosome 2S1 and one on 4S1.

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