Origin of nuclear aberrations and seed shrivelling in triticale: a re-evaluation of the role of C-heterochromatin

The effect of C-heterochromatin on the origin of nuclear aberrations and seed shrivelling was investigated in four triticale lines, each consisting of a pair of genotypes designated A (producing plump, well-filled seeds) and B (with shrivelled seeds). The relative DNA content in the polyploid nuclei of endosperms, 42 h after pollination, was estimated by Feulgen cytophotometry. The observed frequency of polyploid nuclei, 0.85% and 5.69%, respectively, in the two genotypes 1A and 1B caused a reduction in nuclear number of 3.27% and 18.54% at this stage of development. In the B genotype, producing shrivelled grains, polyploidisation started earlier than in the A genotype. An examination of the Giemsa karyotype of the mitotic chromosomes of the rye genome in the four triticale pairs revealed no considerable differences in the banding pattern between the A and B genotypes. Giemsa staining of endosperms, 2-3 days after pollination, clearly showed that bridges without bands, most probably involving wheat chromosomes, were also present. An experiment designed to simulate spindle disturbances in developing endosperms by colchicine treatment revealed that polyploid nuclei can be formed by spindle malfunctions as well.