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 be en 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 ovu les eventually matured into a seed. Aqueous extracts of developing ovu les significantly increased the rate of abortion of the other ovules i n vitro, but the extent of abortion caused by aqueous extracts of mate rnal tissues from fertilized flowers did not differ from the control, implying that the developing ovules may produce a factor that causes t he abortion of other ovules. Silver thiosulfate, an ethylene action in hibitor, significantly reduces the rate of such developing-ovule-media ted abortion in vitro as well as in vivo. This study indicates that ab ortion in S. cuminii is mediated by chemical(s) produced by the develo ping embryo, a possible reflection of ''sibling rivalry'' among develo ping seeds.