As a rule, cultivated vines are monoecious (male and female flowers on the same plant), whereas wild vines are dioecious (separate on different plants). The cultivated monoecious vine has hermaphrodite flowers, i.e. the male and female sexual organs are united in one flower. The purely female wild vines have played an important role in the development of grape varieties. They were dependent on cross-fertilisation and at best they were fertilised by another grape variety, which precluded inbreeding problems. When a grape seed germinated into a seedling, a new grape variety was then created through this natural crossing. In the case of self-pollination (self-fertilisation), negative inbreeding effects largely result in rather inferior offspring. Nature has protected itself from this, so to speak, through dioeciousness or self-sterility. This is because fertilisation with foreign genes leads to positive heterosis effects (changes compared to the parents) in the offspring.
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freier Autor und Weinberater (Fine, Vinum u.a.), Bad Krozingen