Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 246

When the sexes occur on different plants (i.e. there are female plants and male plants), the condition is called dioecy. Examples of dioecious crop species include date, hops, asparagus, spinach, holly, and hemp. The separation of the sexes means that by necessity all seed from dioecious species are hybrid in composition. Where the economic product is the seed or fruit, it is imperative to have female and male plants in the field in an appropriate ratio. In dioecious fruit orchards (e.g. date, persimmons), 3–4 males per 100 females may be adequate. In hops, the commercial product is the female inflorescence. Unfertilized flowers have the highest quality. Consequently, it is not desirable to grow pollinators in the same field when growing hops. Dioecious crops propagated by seed may be improved by mass selection or controlled hybridization.