Abstract
Ovule and seed abortion in Japanese morning glory (Ipomoea nil (L.) Roth.) was investigated to seek the causes for low seed production. Fruit sets in open-pollinated plants were 31% and 36%; numbers of seeds per mature fruit were 3.9 and 2.7; and percentages of mature seeds in total ovules were 17% and 16% for 'Akatsukinomurasaki' and 'Sunsmile Pink', respectively. Aborted ovules or seeds collected at 30 days after pollination (DAP) were smaller than normally developing seeds, although they were larger than unfertilized ovules at anthesis. Success or failure in fertilization could be determined by the presence of pollen tubes in the sections of ovules or developing seeds sampled at 3 DAP, but even unfertilized ovules without pollen tubes enlarged in developing capsules. In aborted ovules or seeds sampled at 4 DAP or later, the structures in embryo sacs degenerated. Observation of sections of aborted ovules or seeds revealed that 64% and 71% of ovules in 'Sunsmile Blue' and 'Akatsukinokurenai', respectively, were not fertilized, and that 5% and 2% of the fertilized ovules in the respective cultivars aborted. In each cultivar, about 4% ovules with a nucellus lacked the embryo sac. We conclude from our data that the high percentage of abortion that leads to low seed production in Japanese morning glory is attributable to the lack of fertilization and zygote formation.
