Early seed development after crossing of trifolium semipilosum and trifolium repens

White, D.W.R.; Williams, E.

New Zealand Journal of Botany 14(2): 161-168

1976


ISSN/ISBN: 0028-825X
Accession: 005206838

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Abstract
Hand pollination of T. semipilosum Fres. var. semipilosum (2n = 16) with pollen from T. repens L. (2n = 32) resulted in fertilization and pod enlargement, but no mature viable seed was produced. The percentage of ovules fertilized was similar to that obtained in compatible intraspecific hand pollinations of T. semipilosum, indicating that the barrier to hybridization between these 2 spp. operates at the post-fertilization stage. Hybrid embryos developed normally up to 4 days after pollination, but subsequently their growth relative to that of normal T. semipilosum embryos became progressively slower. They did not progress beyond the globular stage, and, although still viable on the 8th day, were visibly degenerating by 10-12 days after pollination. Hybrid endosperm development was greatly retarded and ceased altogether at the 16-32-nucleate stage about 4 days after pollination. Endosperm failure appeared to be a major cause of seed failure in this cross. Embryo growth in the first 4 days was apparently independent of endosperm development. Genotypic variation was observed in the degree and frequency of pod enlargement, suggesting that a wider survey for compatible genotypes of these 2 spp. may prove profitable.