Retarded embryo growth and early degeneration of sporophytic tissue are associated with embryo abortion in the interspecific cross Alstroemeria pelegrina × Alstroemeria aurea

Histological studies on crosses between distantly related Alstroemeria species revealed post-fertilization crossing barriers. Developmental events between normal developing seeds (after self-fertilization) and aborting seeds (after cross-fertilization) during 0–32 days after pollination were compared. In both cases the pollen tube remained as a swollen structure inside the micropyle during eight days, and thereafter degenerated. The first division of the zygote occurred within four days after pollination and resulted in a polar two-celled proembryo with a large basal cell and a small apical cell. The self-fertilized embryos developed a polar structure with suspensor and a globular embryo eight days after pollination according to the monocotyledonous type. The cross-fertilized zygotes showed retardation and deviation in plane of the cell plate in the second and third divisions, resulting respectively in linear three-celled and eight-celled proembryos 4–6 days after pollination. Differentiation in suspensor and globular stage embryos proper was not found in the cross-fertilized ovules but in stead aberrant undifferentiated embryos were observed, which formed two groups of cells in later stages. Endosperm development was quite similar in both cases till 12 days after pollination, when the coenocytic endosperm of the self-fertilized ovules formed cell walls around the nuclei, whereas cell wall formation was completely absent in the cross-fertilized ovules. The chalazal nucellus of the cross-fertilized ovules started to degenerate six days after pollination, and presumably restricted the flow of carbohydrates to the developing embryo and endosperm. Subsequently, a loss of contact between the endospermic transfer wall and the chalazal nucellus occurred after twelve days of development. Finally the cross-fertilized embryos aborted after they had lost their contact with the micropylar side of the former embryo sac. Thus, a number of events occurred from the second division of the hybrid zygote onwards, all leading to the abortion of the embryo 18–22 days after pollination. It seemed that during the early cell divisions of the zygote the fate of the embryo was already determined. Embryo abortion was associated with retarded embryo growth and early degeneration of sporophytic tissue. Key words: Alstroemeria spp., interspecific hybridization, embryogenesis, embryo abortion, endosperm degeneration, chalazal nucellus degeneration.