A Histological Study of Seedlessness in Seedless Grapes

Abstract

Histological comparisons were made between seedless cultivars 'Monukka' and 'Mukaku Shiro' and the seeded cultivar 'Campbell Early' to clarify the mechanism of seedlessness in grapes.
1. The percentages of pollen which germinated on agar medium were 41.6, 31.3 and 22.2 for 'Monukka', 'Mukaku Shiro' and 'Campbell Early' respectively.
2. When stigmas of 'Campbell Early' were hand-pollinated with pollen of 'Monukka' and 'Mukaku Shiro', the percentages of berry sets were 61.1 and 38.3, respectively. The percentages of seeded berries of 'Campbell Early' were 98.1 for 'Monukka' and 74.5 for 'Mukaku Shiro' as pollen sources.
3. At anthesis, abnormal outer and inner integuments, the absence of embryo sacs, and imperfect or degenerated eggs were observed more frequently in the seedless cultivars than in the seeded cultivar.
4. Fifteen days after anthesis, the percentages of endosperm that had started nuclear division were 95.9 for 'Campbell Early', 47.6 for 'Monukka', and 20.3 for 'Mukaku Shiro'.
5. Cell division in some zygotes of 'Mukaku Shiro' stopped at the globular embryo stage, whereas in 'Monukka' it ceased when the embryos were heart-shaped.
We conclude that seedlessness in 'Monukka' and 'Mukaku Shiro' is caused by the abortion of ovules and embryo sacs at anthesis and is attributed to (a) lack of fertilization of eggs in the ovules : (b) abortion of the zygote : and (c) cessation of embryo development on account of endosperm degeneration.