| Triticale crossability According to SISODIA and MCGINNIS (1970a, b) the germplasm of 6x wheat, both at the nuclear and cytoplasmic level, is important in the improvement of hexaploid Triticale. Eight Triticale introductions from Salinas, Cal., were therefore crossed as pollen parents with 6 vulgare cultivars and 3 sphaerococcum strains. Many crosses did not yield any viable kernels and an average set of only 1 viable kernel per 100 cross-pollinated florets was obtained (Table 2). Dissection of the F1 kernels at 16 days after pollination revealed that the endosperm was a fluid, degenerate mass and that the embryos were underde-veloped-only 1 out of 21 embryo cultures gave rise to a seedling. The methods employed by KRUSE (1967, 1969) to overcome incompatibility reactions did not improve the set of viable kernels. In the reciprocal crosses (Triticale x common wheat) 23% of the cross-pollinated florets yielded viable kernels. All the durum x Triticale crosses made to date yielded only inviable kernels. Irradiation of Triticale pollen and eggs BREWBAKER and EMERY (1962) stated that irradiation of mature pollen had been tested with only a minor measure of success in overcoming interspecific incompatibilities. They reported that NISHIYAMA and IIZUKA obtained a few viable kernels from two interspecific Avena crosses in 1952 when X-irradiated pollen was used. With this result in mind, and also attempting to induce haploidy in common wheat, gamma-irradiated pollen of various species was used to pollinate emasculated wheat spikes. It was found that irradiated Triticale pollen resulted in a much improved set of viable F1 kernels in the common wheat x 6x Triticale crosses (Table 3, Fig.1). When pollination was effected immediately after pollen irradiation by a 60Co source, the best set of viable F1 kernels was obtained at a gamma-ray dose of 1 kR (15 kR/hr)-at this dose nearly 36% of the cross-pollinated florets yielded viable kernels. Pollination 1 and 3 days after pollen irradiation resulted in peak sets of viable F1 kernels at gamma-ray doses of 1.5 kR and 2 kR, respectively (Table 3, Fig.1). Pollination immediately after the pollen received a gamma-ray dose of 3 kR yielded no viable kernels; when the pollination was effected 3 days afterwards, 14.5 per cent of the florets yielded viable kernels. The most fertile F1 hybrids resulted from Triticale pollen which received a gamma-ray dose of 0.1-0.5 kR; they yielded as many kernels (+ or -4) per F1 spike as the F1 resulting from the control crosses of common wheat x Triticale. Triticale pollen which received a gamma-ray dose of more than 1 kR gave rise to sterile F1 plants. In one family of 13 plants, obtained after the Triticale pollen received a gamma-ray dose of 0.05 kR, a single haploid common-wheat plant with 21 somatic chromosomes was found. In the 6x Triticale x common wheat crosses the production of viable F1 kernels was not improved by irradiating the Triticale parent. The egg cells of Triticale can tolerate a much higher dose of irradiation than the pollen (ca. 7 kR vs. ca. 3 kR). |
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