Out breeding devices are mechanisms or adaptations that promote cross-pollination in flowering plants, helping to maintain genetic diversity and reduce the likelihood of self-pollination (inbreeding).
1. Dichogamy
Dichogamy is the temporal separation of male and female reproductive phases within a single flower. By having the anthers and stigma mature at different times, dichogamy minimizes the chances of self-pollination.
Protandry
In protandry, the anthers release pollen before the stigma becomes receptive. This prevents pollen from the same flower from fertilizing its stigma. As the stigma matures later, the chances of receiving pollen from other plants increase.
Examples of Protandry
In sunflowers, the outer rings of florets (male parts) mature before the central florets (female parts). This staggered development promotes cross-pollination by increasing the window for other pollinators to bring pollen from different plants.
Protogyny
Protogyny is when the stigma becomes receptive before the anthers release pollen. This leads to the same result as protandry—reducing self-pollination and promoting outbreeding.
Examples
In magnolias, the stigma matures first, allowing other pollen to be received before the flower’s own pollen is released. This sequence helps attract beetles and other pollinators, increasing cross-pollination opportunities.
2. Herkogamy (out breeding devices)
Herkogamy involves the spatial separation of the anthers and stigma, reducing the likelihood of pollen from the same flower reaching its stigma. This can occur in several ways:
Physical Barriers
Plants can develop physical structures or arrangements that separate the male and female reproductive parts. These barriers can be natural walls, long styles, or other mechanisms that prevent pollen from falling directly onto the stigma.
Examples
In hibiscus, the long style and stigma are positioned above the anthers, making it unlikely for self-pollination to occur unless assisted by external factors.
Different Flower Positions
In some cases, flowers on the same plant are positioned differently to minimize self-pollination as a result this arrangement increases the likelihood of cross-pollination through animal or wind pollinators.
Examples
In maize (corn), male flowers (tassels) are located at the top of the plant, while female flowers (ears) are lower down. This separation ensures wind-blown pollen from the tassels is less likely to land on the ears of the same plant.
3. Heterostyly (out breeding devices)
Heterostyly is the presence of different floral morphs within the same species, each with distinct arrangements of reproductive organs. This differentiation encourages cross-pollination, as pollen from one morph is unlikely to fertilize the stigma of the same morph.
Pin and Thrum Morphs
In heterostyly, flowers have two or more distinct morphs. “Pin” morphs typically have long styles and shorter stamens, while “thrum” morphs have shorter styles and longer stamens. This configuration promotes cross-pollination because pollen from one morph is most likely to land on the stigma of the other morph.
Examples
Primula species (primroses) exhibit this heterostyly, with pin and thrum flowers. Pollinators are more likely to transfer pollen between different morphs, thus encouraging cross-pollination.
4. Self-Incompatibility
Self-incompatibility (SI) is a genetic mechanism that prevents self-pollination by inhibiting pollen tube growth or preventing fertilization if pollen comes from the same plant or genetically similar individuals. There are two main types:
Gametophytic SI
In gametophytic self-incompatibility, the haploid genotype of the pollen grain determines compatibility. If it matches the haploid genotype of the stigma, the pollen tube’s growth is inhibited, preventing fertilization.
Examples
Solanaceae family (tomatoes, potatoes, and eggplants) exhibit this type of self-incompatibility. Gametophytic SI allows pollen tubes to grow only if they come from a genetically different source
Sporophytic SI
Sporophytic SI is determined by the diploid genotype of the pollen-producing parent. If this genotype matches the genotype of the stigma, the pollen tube does not grow or the pollen is rejected, preventing fertilization.
Examples
Brassica species (cabbages, broccoli, and mustard) show sporophytic SI and this mechanism ensures that cross-pollination occurs between different plants.
5. Monoecy and Dioecy
They are adaptations that separate male and female reproductive organs, either on the same plant or on different plants
Monoecy
In monoecy, plants have separate male and female flowers on the same plant which reduces self-pollination and promotes cross-pollination, as pollen transfer between different flowers is more likely.
Examples
In maize, male flowers are at the top (tassels), and female flowers are lower down (ears) And , In cucumbers, male flowers and female flowers are on the same plant but in different locations.
Dioecy
In dioecy, male and female flowers are on different plants. This setup mandates cross-pollination, as each plant produces only one type of reproductive organ.
Examples
Date palms and kiwifruit have separate male and female plants which require cross-pollination for reproduction. So these are the some Out breeding devices in plants. More
