Abstract

In the cross, S. cereale ♀ x S. africanum ♂, near normal seeds were formed. They showed 40% germination. In the reciprocal cross, S. africanum ♀ x S. cereale ♂, the seeds were dry, brittle, extremely shrivelled at maturity and none germinated. Reciprocal differences as sharp as those in crosses between S. cereale and S. africanum were not noted in crosses of S. cereale with S. montanum or with S. vavilovii. Seeds from the cross S. cereale ♀ x S. montanum ♂ showed 81% germination, whereas seeds from the reciprocal cross S. montanum ♀ x S. cereale ♂ showed 77% germination. Seeds from the cross S. cereale ♀ x S. vavilovii ♂ showed 96% germination, and seeds from the reciprocal cross S. vavilovii ♀ x S. cereale ♂ showed 50% germination. The possible causes of seed inviability which were investigated in S. africanum ♀ x S. cereale ♂ crosses were: (1) endosperm-embryo incompatibility, (2) embryo inviability, (3) maternal tissue-endosperm interaction, (4) abnormal endosperm development. To determine whether an endosperm-embryo incompatibility existed, embryos were transplansted from S. cereale to the seeds of S. africanum as well as to seeds of S. cereale, and also to a paste prepared from both S. africanum seeds and S. cereale seeds. Since S. cereale embryos geminated just as well on S. africanum endosperm as on the endosperm of S. cereale, S. africanum endosperm apparently produced no inhibiting effect on the germination of S. cereale embryos. To determine whether the embryos were viable or inviable in the S. africanum ♀ x S. cereale ♂ seeds, hybrid embryos were excised prior to seed maturity and placed on nutrient agar media. Since four out of twenty-three germinated, and one of these even grew to a vigorous plant when transferred to the soil, the cause of seed failure cannot be attributed to genic failure of the hybrid embryo. To determine whether or not there was abnormal maternal tissue-endosperm development or abnormal endosperm development, seeds were fixed and sectioned at various ages following pollination. Since no abnormalities were observed in the maternal tissue of the hybridseed, seed failure probably cannot be attributed to abnormal maternal tissue-endo sperm relations. However, very marked disturbances in endosperm and embryo development were observed with the eventual disintegration of the endosperm. The cause of seed failure in the cross S. africanum ♀ x S. cereale ♂ is apparently due, therefore, to abnormal development of the endosperm resulting in starvation and death of the embryo.

Degree

College and Department

Life Sciences; Plant and Wildlife Sciences

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