Yearly Fluctuation of Abnormal Embryo Sacs Observed in Japanese Persimmon Diospyros kaki cv. Nishimurawase

Abstract

The relationship between seed abortion and abnormal embryo sacs in Japanese persimmon cv. Nishimurawase, during embryo sac formation was histologically investigated for three years. Abnormal embryo sacs were mainly distinguished into three types; 1) degeneration of embryo sac mother cell (EMC) ; 2) degeneration of embryo sac cell; and 3) multiple embryo sacs in an ovule. Occurrence of degeneration of EMC varied from season to season. It was 9% in 1987, 4% in 1988, and 1-2% in 1989. The percentages of degenerated embryo sac cell for the three years ranged from 10 to 13. Occurrence of multiple embryo sacs in an ovule was 16% in 1987, 8% in 1988, and 18% in 1989. These multiple embryo sacs per ovule are not a factor in seed abortion because at least one egg is fertilized and forms a viable seed. Therefore, the embryo sac abnormalities, which lead to seedlessness, are attributed to the degeneration of the EMC and the embryo sac. The occurrence of 11.6% abnormal embryo sac in 1989 was statistically lower than the 21.8 and 17.5% encountered in 1987 and 1988, respectively. These yearly fluctuations were caused primarily by the degeneration of the EMC. One or two embryo sacs within eight ovules in a flower at anthesis lose their ability to set seed in Japanese persimmon 'Nishimurawase'.