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Material and methods

Seeds of Triticum durum Desf. cultivars Italy363, Kekereiter, Yenminmai and Elytrigia intermedia (Host) Nevski (Thinopyrum intermedium (Host) Barkwath and Dewey) were obtained from Hei Long Jing Academy of Agricultural Sciences, Harbin, China. Tetraploid Elytrigia elongata (Host) Nevski (Thinopyrum intermedium (Host) Barkwath and Dewey) was obtained from Northwest Institute of Botany, ShanXi province and Academia Sinica. The initial hybrids between T.durum and E.intermedia and tetraploid E.elongata were produced by Han et al. (1993) and Han and Li (1993), respectively. The BC₁F₁ plants were obtained by backcrossing of F₁ hybrids with T.durum as male parent. Embryo culture was used to hasten the generation cycle on MS medium. The chromosome numbers were determined from root tip squashes. For meiotic analysis, suitable spikes were fixed in Carnoy's fixative (6:3:1). Pollen mother cells were stained with iron-hematoxylin and squashed in 45% acetic acid.


Results and discussion

1. Production of hexaploid x Trititrigia from Elytrigia intermedia.

The seed sets in the crosses T.durum cv Italy363 x E.intermedia and T.durum cv Kekereiter x E.intermedia were 47.7% and 28.1 %, respectively. Morphology of the F₁ hybrids was intermediate between parents and the hybrids were vigorous but self sterile. BC₁ seed set on the F₁ hybrids using Italy363, Kekereiter, Yenminmai pollen was much lower (0.5% - 2.3%) than the F₁seed set, probably because only unreduced (complete or partial) gametes formed by rare restitution in the F₁ hybrids functioned. Chromosome number of 37 BC₁F₁ plants checked varied from 38 to 49. Twenty-five plants (67.6%) having 2n=49 were likely derived from unreduced gametes of the F₁ hybrids. In the F₁ hybrids, chromosome pairing averaged 21.4_I + 5.6_II + 0.8_III. In the BC₁F₁ plants (2n=49), chromosome pairing averaged 11.2_I + 17.9_II + 0.6_III (Han et al. 1993). The genomic constitution of the F₁ hybrid was ABXE₁E₂ and that of the BC₁F₁ was AABBXE₁E₂. The BC₁F₁ plants showed a low self fertility (6.3%). Progeny of the BC₁F₁ plants were successively selfed to F₅ or F₆ generations. The derivatives showed normal fertility and a high incidence of bivalents in meiosis of progeny of F₆ generation, from which a partial amphiploid was isolated. In the BC₁F₁, the genomes of AABB might have played an important role as pivotal genomes with cushioning action, which in turn produced progeny and hexaploid x Trititrigia were obtained by selection (Fig. 1). The production of the hexaploid x Trititrigia opened a new possibility of gene flowing from E.intermedia to wheat and of developing alien addition and substitution lines for useful characteristics.

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