PLOIDY LEVELS OF DEGENERATED EMBRYOS IN THE CROSSES BETWEEN DIPLOID AND TETRAPLOID CYCLAMEN

Abstract

In reciprocal crosses between diploid and tetraploid cyclamen, almost all zygotic embryos were degenerated. Ploidy levels of the degenerated embryos were, however, obscure. Therefore, embryo rescue by the ovule culture in the crosses were examined. A lot of progenies were obtained in the 2x x 4x crosses, when the ovule culture used medium with coconut water was done 28 days after pollination. Although almost all fruits were dropped 28 days after pollination in the 4x × 2x crosses, some progenies were obtained by the ovule culture at 7-28 days after pollination. Almost all progenies obtained by the ovule culture after the reciprocal crosses between the diploids and tetraploids were triploids, suggesting that many triploid zygotes were formed in the crosses. However, some tetraploid, pentaploid and hexaploid progenies were also obtained. Origin of the pentaploids was suggested the fertilization between a reduced gamete from a diploid plant and an unreduced gamete from a tetraploid plant. These results suggest that many triploid zygotes are formed in the crosses between diploid and tetraploid cyclamen, whereas development of the triploid embryo without the embryo rescue is inhibited. It also shows the possibility that pentaploids and hexaploids as well as triploids and tetraploids can be obtained in the crosses using the ovule culture, depending on the cross combination.