Abnormalities of endosperm development inLilium hybrids

Abstract

Of 191 interspecific crosses attempted between 27 different species representing different subgenera ofLilium only 14 gave rise to seeds and only 6 of these were viable. Sterility was associated with various types of abnormality in endosperm development. Many of these irregularities involved chromosome breakage and reunion but others entailed abnormal DNA replication and chromosome coiling. In one cross the individual endosperm nuclei contained four stranded structures, the behaviour of which at division was similar to that of bivalents at meiosis. The embryo-sac ofLilium is of theFritillaria type, containing both haploid and triploid polar nuclei. As a consequence the balance between the number of chromosome sets in the embryo, endosperm and maternal tissue is 2:5:2 and not 2:3:2 as is more commonly found in diploid species. It is suggested that sterility results from genetic imbalance of the endosperm itself rather than interaction of the endosperm with either embryo or maternal tissue.