Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 211

Four broad and contrasting pairs of reproductive mechanisms or options occur in plants.

 Hermaphrodity versus unisexualityHermaphrodites have both male and female sexual organs and hence may be capable of self‐fertilization. On the other hand, unisexuals, having one kind of sexual organ, are compelled to cross‐fertilize. Each mode of reproduction has genetic consequences, hermaphrodity promoting a reduction in genetic variability, whereas unisexuality, through cross‐fertilization, promotes genetic variability.

 Self‐pollination versus cross‐pollinationHermaphrodites that are self‐fertile may be self‐pollinated or cross‐pollinated. In terms of pollen donation, a species may be autogamous (pollen comes from the same flower – selfing), or allogamous (pollen comes from a different flower). There are finer differences in these types. For example, there may be differences between the time of pollen shed and stigma receptivity.

 Self‐fertilization versus cross‐fertilizationJust because a flower is successfully pollinated does not necessarily mean fertilization would occur. The mechanism of self‐incompatibility causes some species to reject pollen from their own flowers, thereby promoting outcrossing.

 Sexuality versus asexualitySexually reproducing species are capable of providing seed through sexual means. Asexuality manifests in one of two ways – vegetative reproduction (in which no seed is produced), or agamospermy (in which seed is produced).