Pollination

Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds.^[1] Pollinating agents can be animals such as insects, for example beetles or butterflies; birds, and bats; water; wind; and even plants themselves. Pollinating animals travel from plant to plant carrying pollen on their bodies in a vital interaction that allows the transfer of genetic material critical to the reproductive system of most flowering plants.^[2] When self-pollination occurs within a closed flower. Pollination often occurs within a species. When pollination occurs between species, it can produce hybrid offspring in nature and in plant breeding work.

In angiosperms, after the pollen grain (gametophyte) has landed on the stigma, it germinates and develops a pollen tube which grows down the style until it reaches an ovary. Its two gametes travel down the tube to where the gametophyte(s) containing the female gametes are held within the carpel. After entering an ovule through the micropyle, one male nucleus fuses with the polar bodies to produce the endosperm tissues, while the other fuses with the egg cell to produce the embryo.^[3]^[4] Hence the term: "double fertilisation". This process would result in the production of a seed, made of both nutritious tissues and embryo.

In gymnosperms, the ovule is not contained in a carpel, but exposed on the surface of a dedicated support organ, such as the scale of a cone, so that the penetration of carpel tissue is unnecessary. Details of the process vary according to the division of gymnosperms in question. Two main modes of fertilisation are found in gymnosperms: cycads and Ginkgo have motile sperm that swim directly to the egg inside the ovule, whereas conifers and gnetophytes have sperm that are unable to swim but are conveyed to the egg along a pollen tube.

The study of pollination spans many disciplines, such as botany, horticulture, entomology, and ecology. The pollination process as an interaction between flower and pollen vector was first addressed in the 18th century by Christian Konrad Sprengel. It is important in horticulture and agriculture, because fruiting is dependent on fertilisation: the result of pollination. The study of pollination by insects is known as anthecology. There are also studies in economics that look at the positives and negatives of pollination, focused on bees, and how the process affects the pollinators themselves.

Cross-pollination, also called , occurs when pollen is delivered from the stamen of one flower to the stigma of a flower on another plant of the same species.^[8] Plants adapted for cross-pollination have several mechanisms to prevent self-pollination; the reproductive organs may be arranged in such a way that self-fertilisation is unlikely, or the stamens and carpels may mature at different times.^[8]

allogamy

Self-pollination occurs when pollen from one flower pollinates the same flower or other flowers of the same individual. It is thought to have evolved under conditions when pollinators were not reliable vectors for pollen transport, and is most often seen in short-lived annual species and plants that colonize new locations.^[46] Self-pollination may include autogamy, where pollen is transferred from anther (male part) to the stigma (female part) of the same flower; or geitonogamy, when pollen is transferred from anther of a flower to stigma of another flower on the same plant.^[47] Plants adapted to self-fertilize often have similar stamen and carpel lengths. Plants that can pollinate themselves and produce viable offspring are called self-fertile. Plants that cannot fertilize themselves are called self-sterile, a condition which mandates cross-pollination for the production of offspring.^[47]

[45]

: is self-pollination that occurs before the flower opens. The pollen is released from the anther within the flower or the pollen on the anther grows a tube down the style to the ovules. It is a type of sexual breeding, in contrast to asexual systems such as apomixis. Some cleistogamous flowers never open, in contrast to chasmogamous flowers that open and are then pollinated. Cleistogamous flowers are by necessity found on self-compatible or self-fertile plants.^[48] Although certain orchids and grasses are entirely cleistogamous, other plants resort to this strategy under adverse conditions. Often there may be a mixture of both cleistogamous and chasmogamous flowers, sometimes on different parts of the plant and sometimes in mixed inflorescences. The ground bean produces cleistogamous flowers below ground, and mixed cleistogamous and chasmogamous flowers above.^[49]

Cleistogamy

Pollination can be accomplished by cross-pollination or by self-pollination:

An estimated 48.7% of plant species are either dioecious or self-incompatible obligate out-crossers.^[50] It is also estimated that about 42% of flowering plants have a mixed mating system in nature.^[51] In the most common kind of mixed mating system, individual plants produce a single type of flower and fruits may contain self-pollinated, out-crossed or a mixture of progeny types.

Pollination also requires consideration of pollenizers, the plants that serve as the pollen source for other plants. Some plants are self-compatible (self-fertile) and can pollinate and fertilize themselves. Other plants have chemical or physical barriers to self-pollination.

In agriculture and horticulture pollination management, a good pollenizer is a plant that provides compatible, viable and plentiful pollen and blooms at the same time as the plant that is to be pollinated or has pollen that can be stored and used when needed to pollinate the desired flowers. Hybridization is effective pollination between flowers of different species, or between different breeding lines or populations. see also Heterosis.

Peaches are considered self-fertile because a commercial crop can be produced without cross-pollination, though cross-pollination usually gives a better crop. Apples are considered self-incompatible, because a commercial crop must be cross-pollinated. Many commercial fruit tree varieties are grafted clones, genetically identical. An orchard block of apples of one variety is genetically a single plant. Many growers now consider this a mistake. One means of correcting this mistake is to graft a limb of an appropriate pollenizer (generally a variety of crabapple) every six trees or so.

Canadian Pollination Initiative

Cheating (biology)

Floral color change

Pollinator-mediated selection

Fruit tree pollination

Hand-pollination

Paul Knuth

Hermann Müller (botanist)

Plant reproductive morphology

Pollen DNA barcoding

Polli:Nation

(6 October 2020). Pollination: The Enduring Relationship Between Plant and Pollinator. Princeton University Press. pp. 1–224. ISBN 9780691203751.