Crossing of species in the genus trifolium i. trifolium repens x trifolium montanum fertilization and development of the embryo and endosperm

Kazimierska, E.M.; Kazimierski, T.

Genetica Polonica 26(3): 327-340


Accession: 005070450

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These studies present a subsequent attempt to explain causes of failure in interspecific crosses within the genus Trifolium. While crossing T. repens with T. montanum species, the fertilization and development of the embryo and endosperm were studied. It has appeared that the studied species show genetic and zygotic compatibility limited by heterogeneity of reproductive cells within an individual. Genetic differentiation of gametes causes that after reciprocal interspecific crossing the percentage of fertilized ovules was lower than that after cross-pollination within a species. Hybrid embryos developed slowly and died 3-5 days after pollination. In the cases, when after zygote division there occurs a cell wall parallel to the longitudinal axis of the embyro sac, the cells of the so formed embryo did not divide any more. Nuclei of hybrid endosperm (tetra- and pentaploid) had on average a larger diameter than tri- and hexaploid endosperm of plants of the parental species. These differences are considered to be an expression of incomplete homology of chromosome complements, fused in a hybrid nucleus, two of which originate from a female partner and others - from the male. Other than in the parental species differences in the size, shape and role of the integumental tapetum cells in ovules with a hybrid embryo were a consequence of a weak and slow development of the hybrid embryo and endosperm. One of the main reasons of the so-far failures in obtaining interspecific hybrids in the genus Trifolium should be incompatibility, intensifying with the passage of time after fertilization. It leads to inhibition of cell division of the embryo, nuclei and endosperm and, in consequence, to atrophy of a hybrid system.