Early seed development after crossing of <i>Trifolium ambiguum</i> and <i>T. repens</i>

Abstract Hand pollination of Trifolium ambiguum Bieb. (2n = 4x = 32) with pollen from T. repens L. (2n = 32) resulted in fertilisation and pod enlargement, but no mature viable seed was produced. Hybrid embryos and endosperms were developmentally more advanced than those of T. ambiguum (4x) controls for the first 2 days after pollination. Subsequently hybrid embryo growth slowed, and although an advanced globular or early “heart” stage was attained at 5–6 days after pollination normal differentiation did not proceed beyond this stage and almost all embryos were visibly degenerating by 7–9 days after pollination. Occasional abnormal undifferentiated or partially differentiated embryos were found still showing substantial numbers of cell divisions at 10–13 days after pollination. Hybrid endosperms varied in their development, but never exceeded the 128‐nucleate level. By 5 days after pollination all were degenerating. Endosperm failure appears to be a major cause of seed failure in this cross.

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