Cytological Evidence for Fertilization in Hexaploid Wheat × Sorghum Crosses

Abstract

AbstractCrosses were made between the hexaploid wheat ‘Chinese Spring’ (2n = 42) and the diploid grain sorghum ‘S9B’ (2n = 20). Sixty‐nine out of 100 florets fixed 48 h after pollination contained an embryo, an endosperm, or both, a remarkably high frequency in view of the taxonomic distance spanned by the cross. Percentages of single or double fertilization ranged from 50 % to 91 % for individual spikes. The hybrid origin of the embryos was confirmed by examining zygotes from spikes fixed 25 to 27 h after pollination. Seven of the 8 zygotes in which chromosomes were sufficiently contracted to be counted contained 21 large wheat chromosomes and 10 much smaller sorghum chromosomes. The eighth contained 21 chromosomes from wheat and 20 from sorghum. Sorghum chromosomes did not appear to be attached to the spindle in zygote nietaphases and showed no evidence of movement towards the spindle poles in the single zygote anaphase found. Embryos with two or more cells invariably contained one or more micronuclei and metaphases in embryos with three or more cells contained only 21 wheat chromosomes showing that sorghum chromosomes were rapidly eliminated. Endosperm, when present, was always highly abnormal.