| The effect of the D-genome on kernel set and viability
in wheat x rye crosses R. DE V. PIENAAR and G.F. MARAIS Department of Genetics, University of Stellenbosch, and Department of Agricultural Technical Services, W.R.R., Stellenbosch 7600, South Africa. The viability of the hybrid kernels resulting from crossing diploid and tetraploid wheats with diploid rye (S. cereale) is very poor and generally much lower than those obtained from crossing the hexaploid wheats with rye (OEHLER 1931; KATTERMANN 1941; KROWLOW 1970; LEIGHTY and SANDO 1928; PIENAAR 1973). Although the poor germinability of the hybrid kernels can to a certain extent be overcome by means of embryo culture methods (ROMMEL 1958, 1960; KRUSE 1974), it remains one of the major obstacles for the triticale breeder in the production of new primary triticale lines. KROWLOW (1964, 1970, 1973) found that the viability of the hybrid kernels obtained by crossing T. monococcum and the tetraploid wheats with diploid S.cereale was 0% and 1.04% respectively. However, when he crossed the AAAABB autoallohexaploids (obtained by hybridising the tetraploid wheats T. timopheevi, T. dicoccum, T. turgidum, T. durum and T. carthlicum, with T. monococcum and doubling the chromosome number of the resulting hybrids) with diploid rye, kernels with a viability of 60.99% were produced. This figure agrees well with the 61.83% germinability of the hybrid kernels obtained from crossing the hexaploid bread wheats with rye. KROWLOW (1970) believed that the good germinability of the hybrid kernels produced by the latter cross was due to the hexaploid nature of the wheat parent which resulted from the addition of the D-genome to the primitive cultivated tetraploid wheats during the evolution of the bread wheats. KROWLOW (op. cit.) concluded that the higher viability of the hybrid kernels produced by 6x wheat x 2x rye crosses, compared to 4x wheat x 2x rye crosses does not result from the action of a specific genome, but is due to the increase of the number of wheat genomes relative to the rye genome. KROWLOW (1973) crossed diploid (AA), tetraploid (AAAA and AABB) and hexaploid (AAAABB) wheats with both diploid and tetraploid rye, and obtained evidence which substantiated his belief that the relative amount of wheat and rye genomes in the F1 kernels controls their viability; the best viability was obtained when the wheat parent was hexaploid and the rye diploid. The present study was undertaken to determine the effect of the addition (by hybridisation and amphiploidy) of the D-genome of various Ae. squarrosa varieties to a number of tetraploid wheats on the crossability with rye and the germinability of the resulting kernels. Material and Methods The material listed in Table 1 was used as female parents. All entries except the T. aestivum ssp. vulgare cv. Flameks and the T. aestivum ssp. sphaerococcum line listed, were kindly supplied by Dr. E.R. KERBER, Canada Department of Agriculture, Winnipeg, Manitoba, Canada. The rye cultivars Maroc and Weser, respectively introductions from Europe and the U.S.A., were used as pollen parents. All crosses were made in a growth chamber with a dark/light period of 12/12 hours and dark/light temperature of 10/16C. The kernels were germinated in Petri-dishes 2 to 3 months after the ripe ears were harvested. |
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