| Meiotic associations in a Triticum turgidum
L. var. durum Desf. em. Bowden x Agropyron distichum (Thunb.)
Beauv. hybrid R. DE V. PIENAAR Department of Genetics, University of stellenbosch South Africa. The successful crosses of the two hexaploid bread wheat cultivars Chinese Spring and Inia 66 with Agropyron distichum (PIENAAR et al, 1977; PIENAAR, 1979), tempted us to produce a T. turgidum var. durum x A. distichum hybrid. The latter two species are both tetraploid with 2n=28, and their amphiploid should therefore be octoploid with 2n=56. Since the optimal chromosome number of many of the polyploid Triticinae is 2n=42, it was thought that the T. durum x A. distichum octoploid would probably be more vigorous than the decaploid amphiploid obtained from the T. aestivum var. aestivum x A. distichum hybrid (PIENAAR, 1980). During the early summer of 1977 and 1978 some 3744 durum-wheat florets were emasculated and pollinated with A. distichum (Table 1). None of these crosses yielded any filled kernels, but 23 shrivelled and 9 small kernels with undeveloped endo-sperm were obtained. The 9 embryos from the latter kernels were excised 18 days after pollination and cultured on sterile Orchid Agar in McCarthney bottles. Seven of these embryos developed into plantlets on the medium and were transplanted into pots at the three leaf stage. Five of these grew into vigorous F1 hybrids with 2n=28 chromosomes. Both the Calvin and Nordum F1 hybrids with A. distichum are much more vigorous than the F1 hybrid of Inia 66 x A. distichum and like the latter, tend to be perennial. They produce numerous tillers with large errect leaves. The height of the Calvin hybrid is 97 cm, that of the Nordum hybrid 122 cm, compared to the 97 cm of the Inia 66 hybrid. Although Calvin, Nordum and Inia 66 are awned cultivars, their hybrids with A. distichum differ in the expression of the awned character; the spikes of the Calvin and Nordum hybrids have short awns, whereas the Inia 66 hybrid has tip awns only. However, the latter hybrid resembles its Inia 66 parent in having a non-brittle spike with a strong rachis, whereas the durum-hybrids have brittle spikes like A. distichum. The spikes of the Calvin and Nordum F1 hybrids have 21 and 18 spiklets respectively, and the respective spikelets possess 8 and 6-7 florests. The spikes of the Calvin hybrid tend to be branched; the lower spikelets being replaced by branches with up to 7 spikelets. Both F1 hybrids are completely selfsterile like the Inia 66 hybrid. |
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