Factors affecting embryo abortion in Syzygium cuminii (L.) skeels (Myrtaceae)

The possible causes of low seed set in Syzygium cuminii, a woody tree bearing flowers with many ovules but fruits with single seeds, have been investigated. Pollen grain limitation and lack of fertilization do not completely explain the single seededness of fruits indicating the involvement of postfertilization factors. Developing ovules exhibited a clear pattern during the early fruit growth, and only one of the ovules eventually matured into a seed. Aqueous extracts of developing ovules significantly increased the rate of abortion of the other ovules in vitro, but the extent of abortion caused by aqueous extracts of maternal tissues from fertilized flowers did not differ from the control, implying that the developing ovules may produce a factor that causes the abortion of other ovules. Silver thiosulfate, an ethyleneaction inhibitor, significantly reduces the rate of such developing-ovule-mediated abortion in vitro as well as in vivo This study indicates that abortion in S. cuminii is mediated by chemical(s) produced by the developing embryo, a possible reflection of "sibling rivalry" among developing seeds