Embryo Development in Crosses between Diploid and Tetraploid Cyclamen (Cyclamen persicum Mill.).

Abstract

Pollen tube growth and the development of zygotic embryos in reciprocal crosses between diploid and tetraploid cyclamen cultivars (Cyclamen persicum) were observed to understand why few seeds formed and no triploid progenies resulted from the crosses.In all cross combinations, many pollen tubes entered the ovules within 4 days after pollination. These results suggest that the difficulty in obtaining seeds in cyclamen crossesbetween diploid and tetraploid was not attributable to the lack of pollen tube growth.The degeneration of zygotic embryoswas observed approximately 5 weeks after pollination (WAP) in 2x × 4x and 4x × 2x crosses. In 2x × 4x, the degeneration of embryos was observed in most of the ovules 9 WAP, although about 20 % of ovules had globularembryos 7 WAP. No globular embryo was observed in 4x × 2x using diploid, 'Pure White' having no giant pollen grains. On the other hand, a few matured embryos, which seemedto exhibit tetraploidy, were observed in 4x × 2x using diploid, 'Pure White' having giant pollen grains. These results suggest that the difficulty in obtaining seeds, triploid seeds in particular, in reciprocal crosses between diploid and tetraploid cyclamen cultivars wasdue to the degeneration of zygotic embryos.The endosperm did not become cellular but was observed to degenerate in most of theovules of 2x × 4x and 4x × 2x crosses. It is, therefore, suggested that the degeneration of zygotic embryos was caused by the defective endosperm or the lack of its development inthe cyclamen crosses between diploid and tetraploid cultivars.