Self-pollination

Self-pollination is when pollen from the same plant arrives at the stigma of a flower (in flowering plants) or at the ovule (in gymnosperms). There are two types of self-pollination: in autogamy, pollen is transferred to the stigma of the same flower; in geitonogamy, pollen is transferred from the anther of one flower to the stigma of another flower on the same flowering plant, or from microsporangium to ovule within a single (monoecious) gymnosperm. Some plants have mechanisms that ensure autogamy, such as flowers that do not open (cleistogamy), or stamens that move to come into contact with the stigma. The term selfing that is often used as a synonym, is not limited to self-pollination, but also applies to other types of self-fertilization.

Ophrys apifera flower2
One type of automatic self-pollination occurs in the orchid Ophrys apifera. One of the two pollinia bends itself towards the stigma.

Occurrence

Few plants self-pollinate without the aid of pollen vectors (such as wind or insects). The mechanism is seen most often in some legumes such as peanuts. In another legume, soybeans, the flowers open and remain receptive to insect cross pollination during the day. If this is not accomplished, the flowers self-pollinate as they are closing. Among other plants that can self-pollinate are many kinds of orchids, peas, sunflowers and tridax. Most of the self-pollinating plants have small, relatively inconspicuous flowers that shed pollen directly onto the stigma, sometimes even before the bud opens. Self-pollinated plants expend less energy in the production of pollinator attractants and can grow in areas where the kinds of insects or other animals that might visit them are absent or very scarce—as in the Arctic or at high elevations.

Self-pollination limits the variety of progeny and may depress plant vigor. However, self-pollination can be advantageous, allowing plants to spread beyond the range of suitable pollinators or produce offspring in areas where pollinator populations have been greatly reduced or are naturally variable.[1]

Pollination can also be accomplished by cross-pollination. Cross-pollination is the transfer of pollen, by wind or animals such as insects and birds, from the anther to the stigma of flowers on separate plants.

Types of flowers that self pollinate

Both hermaphrodite and monoecious species have the potential for self-pollination leading to self-fertilization unless there is a mechanism to avoid it. Eighty percent of all flowering plants are hermaphroditic, meaning they contain both sexes in the same flower, while 5 percent of plant species are monoecious. The remaining 15% would therefore be dioecious (each plant unisexual). Plants that self-pollinate include several types of orchids, and sunflowers. Dandelions are also capable of self-pollination as well as cross-pollination.

Advantages of self-pollination

There are several advantages for self-pollinating flowers. Firstly, if a given genotype is well-suited for an environment, self-pollination helps to keep this trait stable in the species. Not being dependent on pollinating agents allows self-pollination to occur when bees and wind are nowhere to be found. Self-pollination can be an advantage when the number of flowers is small or they are widely spaced. During self-pollination, the pollen grains are not transmitted from one flower to another. As a result, the wastage of pollen is less. Also, it does not depend on any external carrier. The plant that develops in that way of pollination cannot make changes in their characters and so the features of a species can be maintained. This way, a species can maintain purity in it.

Disadvantages of self-pollination

The disadvantages of self-pollination come from a lack of variation that allows no adaptation to the changing environment or potential pathogen attack. Self-pollination can lead to inbreeding depression caused by expression of deleterious recessive mutations,[2] or to the reduced health of the species, due to the breeding of related specimens. This is why many flowers that could potentially self-pollinate have a built-in mechanism to avoid it, or make it second choice at best. Genetic defects in self-pollinating plants cannot be eliminated by genetic recombination and offspring can only avoid inheriting the deleterious attributes through a chance mutation arising in a gamete.

Mixed mating

About 42% of flowering plants exhibit a mixed mating system in nature.[3] In the most common kind of system, individual plants produce a single flower type and fruits may contain self-pollinated, out-crossed or a mixture of progeny types. Another mixed mating system is referred to as dimorphic cleistogamy. In this system a single plant produces both open, potentially out-crossed and closed, obligately self-pollinated cleistogamous flowers.[4]

Self-pollinating species

The evolutionary shift from outcrossing to self-fertilization is one of the most common evolutionary transitions in plants. About 10-15% of flowering plants are predominantly self-fertilizing.[5] A few well-studied examples of self-pollinating species are described below.

Paphiopedilum parishii

Self-pollination in the slipper orchid Paphiopedilum parishii occurs when the anther changes from a solid to a liquid state and directly contacts the stigma surface without the aid of any pollinating agent.[6]

Holcoglossum amesianum

The tree-living orchid Holcoglossum amesianum has a type of self-pollination mechanism in which the bisexual flower turns its anther against gravity through 360° in order to insert pollen into its own stigma cavity---without the aid of any pollinating agent or medium. This type of self-pollination appears to be an adaptation to the windless, drought conditions that are present when flowering occurs, at a time when insects are scarce.[7] Without pollinators for outcrossing, the necessity of ensuring reproductive success appears to outweigh potential adverse effects of inbreeding. Such an adaptation may be widespread among species in similar environments.

Caulokaempferia coenobialis

In the Chinese herb Caulokaempferia coenobialis a film of pollen is transported from the anther (pollen sacs) by an oily emulsion that slides sideways along the flower’s style and into the individual’s own stigma.[8] The lateral flow of the film of pollen along the style appears to be due solely to the spreading properties of the oily emulsion and not to gravity. This strategy may have evolved to cope with a scarcity of pollinators in the extremely shady and humid habitats of C. coenobialis.

Capsella rubella

Capsella rubella (Red Shepard’s purse)[9][10] is a self-pollinating species that became self-compatible 50,000 to 100,000 years ago, indicating that self-pollination is an evolutionary adaptation that can persist over many generations. Its out-crossing progenitor was identified as Capsella grandiflora.

Arabidopsis thaliana

Arabidopsis thaliana is a predominantly self-pollinating plant with an out-crossing rate in the wild estimated at less than 0.3%.[11] A study suggested that self-pollination evolved roughly a million years ago or more.[12]

Bulbophyllum bicoloratum

Self-pollination in the Madagascan orchid Bulbophyllum bicoloratum occurs by virtue of a rostellum that may have regained its stigmatic function as part of the distal median stigmatic lobe.[13]

Possible long-term benefit of meiosis

Meiosis followed by self-pollination produces little overall genetic variation. This raises the question of how meiosis in self-pollinating plants is adaptively maintained over extended periods [i.e. for roughly a million years or more, as in the case of A.thaliana[12]] in preference to a less complicated and less costly asexual ameiotic process for producing progeny. An adaptive benefit of meiosis that may explain its long-term maintenance in self-pollinating plants is efficient recombinational repair of DNA damage.[14][15] This benefit can be realized at each generation (even when genetic variation is not produced).

See also

References

  1. ^ Grossenbacher D, Briscoe Runquist R, Goldberg EE, Brandvain Y (2015). "Geographic range size is predicted by plant mating system". Ecol. Lett. 18 (7): 706–13. doi:10.1111/ele.12449. PMID 25980327.
  2. ^ Charlesworth D, Willis JH (2009). "The genetics of inbreeding depression". Nat. Rev. Genet. 10 (11): 783–96. doi:10.1038/nrg2664. PMID 19834483.
  3. ^ Goodwillie C, Kalisz S, Eckert CG (2005) The evolutionary enigma of mixed mating systems in plants: Occurrence, theoretical explanations, and empirical evidence. Annu. Rev. Ecol. Evol. Syst. 36: 47-79. doi:10.1146/annurev.ecolsys.36.091704. 175539
  4. ^ Munguía-Rosas MA, Campos-Navarrete MJ, Parra-Tabla V (2013). "The effect of pollen source vs. flower type on progeny performance and seed predation under contrasting light environments in a cleistogamous herb". PLoS ONE. 8 (11): e80934. doi:10.1371/journal.pone.0080934. PMC 3829907. PMID 24260515.
  5. ^ Wright SI, Kalisz S, Slotte T (June 2013). "Evolutionary consequences of self-fertilization in plants". Proc. Biol. Sci. 280 (1760): 20130133. doi:10.1098/rspb.2013.0133. PMC 3652455. PMID 23595268.
  6. ^ Chen LJ, Liu KW, Xiao XJ, Tsai WC, Hsiao YY, Huang J, Liu ZJ (2012). "The anther steps onto the stigma for self-fertilization in a slipper orchid". PLoS ONE. 7 (5): e37478. doi:10.1371/journal.pone.0037478. PMC 3359306. PMID 22649529.
  7. ^ Liu KW, Liu ZJ, Huang L, Li LQ, Chen LJ, Tang GD (June 2006). "Pollination: self-fertilization strategy in an orchid". Nature. 441 (7096): 945–6. doi:10.1038/441945a. PMID 16791185.
  8. ^ Wang Y, Zhang D, Renner SS, Chen Z (September 2004). "Botany: a new self-pollination mechanism". Nature. 431 (7004): 39–40. doi:10.1038/431039b. PMID 15343325.
  9. ^ Brandvain Y, Slotte T, Hazzouri KM, Wright SI, Coop G (2013). "Genomic identification of founding haplotypes reveals the history of the selfing species Capsella rubella". PLoS Genet. 9 (9): e1003754. doi:10.1371/journal.pgen.1003754. PMC 3772084. PMID 24068948.
  10. ^ Slotte T, Hazzouri KM, Ågren JA, Koenig D, Maumus F, Guo YL, Steige K, Platts AE, Escobar JS, Newman LK, Wang W, Mandáková T, Vello E, Smith LM, Henz SR, Steffen J, Takuno S, Brandvain Y, Coop G, Andolfatto P, Hu TT, Blanchette M, Clark RM, Quesneville H, Nordborg M, Gaut BS, Lysak MA, Jenkins J, Grimwood J, Chapman J, Prochnik S, Shu S, Rokhsar D, Schmutz J, Weigel D, Wright SI (July 2013). "The Capsella rubella genome and the genomic consequences of rapid mating system evolution". Nat. Genet. 45 (7): 831–5. doi:10.1038/ng.2669. PMID 23749190.
  11. ^ Population genetic structure and outcrossing rate of Arabidopsis thaliana (L.) Heynh. Abbott RJ, Gomes MF. Heredity 1989 62:411-418
  12. ^ a b Tang C, Toomajian C, Sherman-Broyles S, Plagnol V, Guo YL, Hu TT, Clark RM, Nasrallah JB, Weigel D, Nordborg M (August 2007). "The evolution of selfing in Arabidopsis thaliana". Science. 317 (5841): 1070–2. doi:10.1126/science.1143153. PMID 17656687.
  13. ^ Gamisch A, Staedler YM, Schönenberger J, Fischer GA, Comes HP (2013). "Histological and Micro-CT Evidence of Stigmatic Rostellum Receptivity Promoting Auto-Pollination in the Madagascan Orchid Bulbophyllum bicoloratum". PLoS ONE. 8 (8): 1–10. doi:10.1371/journal.pone.0072688.
  14. ^ Bernstein H, Hopf FA, Michod RE. (1987). The molecular basis of the evolution of sex. Adv Genet 24:323-70. Review. PMID 3324702
  15. ^ Harris Bernstein, Carol Bernstein and Richard E. Michod (2011). Meiosis as an Evolutionary Adaptation for DNA Repair. Chapter 19 in DNA Repair. Inna Kruman editor. InTech Open Publisher. doi:10.5772/25117 http://www.intechopen.com/books/dna-repair/meiosis-as-an-evolutionary-adaptation-for-dna-repair
Amorphophallus titanum

Amorphophallus titanum, also known as the titan arum, is a flowering plant with the largest unbranched inflorescence in the world. The titan arum's inflorescence is not as large as that of the talipot palm, Corypha umbraculifera, but the inflorescence of the talipot palm is branched rather than unbranched. The species is endemic to Sumatra.

Due to its odor, which is like the smell of a rotting corpse or carcass, the titan arum is characterized as a carrion flower, and is also known as the corpse flower or corpse plant (Indonesian: bunga bangkai—bunga means flower, while bangkai can be translated as corpse, cadaver, or carrion). For the same reason, the title corpse flower is also attributed to the genus Rafflesia.

Arabidopsis thaliana

Arabidopsis thaliana, the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. A. thaliana is considered a weed; it is found by roadsides and in disturbed land.

A winter annual with a relatively short life cycle, A. thaliana is a popular model organism in plant biology and genetics. For a complex multicellular eukaryote, A. thaliana has a relatively small genome of approximately 135 megabase pairs (Mbp). It was the first plant to have its genome sequenced, and is a popular tool for understanding the molecular biology of many plant traits, including flower development and light sensing.

Autogamy

Autogamy, or self-fertilization, refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species of protists have also been observed using autogamy as a means of reproduction. Flowering plants engage in autogamy regularly, while the protists that engage in autogamy only do so in stressful environments.

Bensoniella

Bensoniella is a monotypic genus of plants in the saxifrage family containing the single species Bensoniella oregona (also, B. oregana), which is known by the common name Oregon bensoniella, or simply bensoniella. This plant is endemic to the Klamath Mountains of northern California and southern Oregon. This is a plant of the wet forest understory and meadows above 1000 meters in elevation. It is a perennial herb which grows from a rhizome and bears rounded to heart-shaped lobed leaves with woolly petioles and tall, thin racemes of flowers. Each flower is white with bright yellow-pink anthers. The plant produces capsules of abundant seeds but also reproduces vegetatively. When it does reproduce sexually, it often self-pollinates. Bensoniella is not endangered but it is a species of some concern for several reasons, including lack of genetic diversity in part due to its habit of self-pollination and asexual reproduction, its relatively narrow tolerance of habitats, its small range of distribution, habitat destruction due to logging, grazing, and road-building, and erosion. The plant was first collected in 1916 by John Hunter Thompson.

Clarkia unguiculata

Clarkia unguiculata is a species of wildflower known by the common name elegant clarkia or mountain garland. This plant is endemic to California, where it is found in many woodland habitats. Specifically it is common on the forest floor of many oak woodlands, along with typical understory wildflowers that include Calochortus luteus, Cynoglossum grande and Delphinium variegatum. C. unguiculata presents a spindly, hairless, waxy stem not exceeding a meter in height and bears occasional narrow leaves. The showy flowers have hairy, fused sepals forming a cup beneath the corolla, and four petals each one to 2.5 centimeters long. The paddle-like petals are a shade of pink to reddish to purple and are slender and diamond-shaped or triangular. There are eight long stamens, the outer four of which have large red anthers. The stigma protrudes from the flower and can be quite large. Flowers of the genus Clarkia are primarily pollinated by specialist bees found in their native habitat "Clarkias independently developed self-pollination in 12 lineages."

Cleistogamy

Cleistogamy is a type of automatic self-pollination of certain plants that can propagate by using non-opening, self-pollinating flowers. Especially well known in peanuts, peas, and pansy this behavior is most widespread in the grass family. However, the largest genus of cleistogamous plants is Viola.

The more common opposite of cleistogamy, or "closed marriage", is called chasmogamy, or "open marriage". Virtually all plants that produce cleistogamous flowers also produce chasmogamous ones. The principal advantage of cleistogamy is that it requires fewer plant resources to produce seeds than does chasmogamy, because development of petals, nectar and large amounts of pollen is not required. This efficiency makes cleistogamy particularly useful for seed production on unfavorable sites or adverse conditions. Impatiens capensis, for example, has been observed to produce only cleistogamous flowers after being severely damaged by grazing and to maintain populations on unfavorable sites with only cleistogamous flowers. The obvious disadvantage of cleistogamy is that self-fertilization occurs, which may suppress the creation of genetically superior plants.For genetically modified (GM) rapeseed, researchers hoping to minimise the admixture of GM and non-GM crops are attempting to use cleistogamy to prevent gene flow. However, preliminary results from Co-Extra, a current project within the EU research program, show that although cleistogamy reduces gene flow, it is not at the moment a consistently reliable tool for biocontainment; due to a certain instability of the cleistogamous trait, some flowers may open and release genetically modified pollen.

Fertilisation

Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, insemination, pollination, fecundation, syngamy and impregnation, is the fusion of gametes to initiate the development of a new individual organism or offspring. This cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.

Fruit tree pollination

Pollination of fruit trees is required to produce seeds with surrounding fruit. It is the process of moving pollen from the anther to the stigma, either in the same flower or in another flower. Some tree species, including many fruit trees, do not produce fruit from self-pollination, so pollinizer trees are planted in orchards.

The pollination process requires a carrier for the pollen, which can be animal, wind, or human intervention (by hand-pollination or by using a pollen sprayer). Cross pollination produces seeds with a different genetic makeup from the parent plants; such seeds may be created deliberately as part of a selective breeding program for fruit trees with desired attributes. Trees that are cross-pollinated or pollinated via an insect pollinator produce more fruit than trees with flowers that just self-pollinate. In fruit trees, bees are an essential part of the pollination process for the formation of fruit.Pollination of fruit trees around the world has been highly studied for hundreds of years. There is a lot of information known about fruit tree pollination from temperate climates, but much less is known about fruit tree pollination from tropical climates. Fruits from temperate climates include apples, pears, plums, peaches, cherries, berries, grapes, and nuts which are considered dry fruits. Fruits from tropical climates include bananas, pineapples, papayas, passion fruit, avocado, mango, and members of the genus Citrus.

Geitonogamy

Geitonogamy (from Greek geiton (γείτων) = neighbor + gamein (γαμεῖν) = to marry) is a type of self-pollination. Geitonogamous pollination is sometimes distinguished from the fertilizations that can result from it, geitonogamy. If a plant is self-incompatible, geitonogamy can reduce seed production.Geitonogamy is when pollen is exported using a vector (pollinator or wind) out of one flower but only to another flower on the same plant. It is a form of self-fertilization.

In flowering plants, pollen is transferred from a flower to another flower on the same plant, and in animal pollinated systems this is accomplished by a pollinator visiting multiple flowers on the same plant. Geitonogamy is also possible within species that are wind-pollinated, and may actually be a quite common source of self-fertilized seeds in self-compatible species. It also occurs in monoecious gymnosperms. Although geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant.

Monoecious plants like maize show geitonogamy. Geitonogamy is not possible for strictly dioecious plants.

Hibiscus trionum

Hibiscus trionum, commonly called flower-of-an-hour, bladder hibiscus, bladder ketmia, bladder weed, flower-of-the-hour, modesty, puarangi, shoofly, and venice mallow, is an annual plant native to the Old World tropics and subtropics. It has spread throughout southern Europe both as a weed and cultivated as a garden plant. It has been introduced to the United States as an ornamental where it has become naturalized as a weed of cropland and vacant land, particularly on disturbed ground.

The plant grows to a height of 20–50 centimetres (7.9–19.7 in), sometimes exceeding 80 centimetres (31 in), and has white or yellow flowers with a purple centre. In the deeply pigmented centre of the flower, the surface features striations, which have been the subject of controversy about whether they act as a diffraction grating, creating iridescence.

The pollinated but unripe seedpods look like oriental paper lanterns, less than an inch across, pale green with purple highlights.

The flowers of the Hibiscus trionum can set seed via both outcrossing and self-pollination. During the first few hours after anthesis, the style and stigma are erect and receptive to receive pollen from other plants. In the absence of pollen donation, the style bends and makes contact with the anthers of the same flower, inducing self-pollination. Although outcrossing plants seem to perform better than self-pollinating plants, this form of reproductive assurance might have contributed to the success of H. trionum plants in several environments.

Hybrid rice

Hybrid rice is grown from hybrid rice seed which is produced by growing an inbred rice variety having sterile pollen which is cross pollinated with normal pollen from adjacent rice plants of a different inbred variety. Hybrid rice therefore has two genetically different parents. As with other types of hybrids, hybrid rice typically displays heterosis (or hybrid vigor) such that when it is grown under the same conditions as comparable high-yielding inbred rice varieties it can produce up to 30% more rice. High-yield crops, like hybrid rice, are one of the most important tools for combating world food crises.

The first hybrid rice varieties were released in China.In crop breeding, although the use of heterosis in first-generation seeds (or F1) is well known, its application in rice was limited because of the self-pollination character of that crop. In 1974, Chinese scientists successfully transferred the male sterility gene from wild rice to create the cytoplasmic genetic male-sterile (CMS) line and hybrid combination. The first generation of hybrid rice varieties were three-line hybrids and produced yields that

were about 15 to 20 percent greater than those of improved or high-yielding varieties of the same growth duration.

Chinese scientist Yuan Longping,"the Father of Hybrid rice", is the most famous researchers on hybrid rice. In the 1960s, he made his seminal discovery of the genetic basis of heterosis in rice. This was a unique discovery because it had been previously thought that heterosis was not possible for self-pollinating crops such as rice. According to the China Daily, in 2011, Yuan developed a new hybrid rice that can produce 13.9 tons of rice per hectare.Another Chinese agronomist, Li Zhengyou, developed the Dian (or Yunnan)-type hybrid rice, and was a pioneer in the research of high-altitude hybrid rice. He published the book Dian-type Hybrid Rice (滇型杂交水稻).In China, hybrid rice is estimated to be planted on more than 50% of rice-growing land there and it is credited with helping the country increase its rice yields, which are among the highest within Asia. Hybrid rice is also grown in many other important rice producing countries including Indonesia, Vietnam, Myanmar, Bangladesh, India, Sri Lanka, Brazil, USA, and the Philippines. A 2010 study published by the International Rice Research Institute (IRRI), reports that the profitability of hybrid rice in three Indian states varied from being equally profitable as other rice to 34% more profitable.Outside of China other institutes are also researching hybrid rice, including the International Rice Research Institute, which also coordinates the Hybrid Rice Development Consortium.

Levenhookia

Levenhookia, also known as the styleworts, is a genus of ten recognized species in the family Stylidiaceae and is endemic to Australia. The genus is restricted to Western Australia almost exclusively with a few exceptions: L. pusilla's range extends into South Australia, L. dubia's range extends through South Australia into Victoria and New South Wales, L. sonderi is native only to Victoria, and L. chippendalei is also found in the Northern Territory.All species of Levenhookia possess a sensitive labellum that performs a similar function to the column of Stylidium species. The labellum responds to touch and enables the plants to promote cross-pollination and avoid self-pollination. Most species of Levenhookia are ephemeral plants that prefer sand heath habitat. Levenhookia species also possess glandular trichomes similar to those of its sister genus, Stylidium. While no studies have been done to test Levenhookia for carnivory, it is plausible that they are carnivorous plants like the related Stylidium species.

Monocotyledon reproduction

The monocots (or Monocotyledons) are one of the two major clades of flowering plants (or Angiosperms), the other being the dicots (or dicotyldons). In order to reproduce they utilize various strategies such as employing forms of asexual reproduction, restricting which individuals they are sexually compatible with, or influencing how they are pollinated. Nearly all reproductive strategies that evolved in the dicots have independently evolved in monocots as well. Despite these similarities and their close relatedness, monocots and dicots have distinct traits in their reproductive biologies.

Most monocots reproduce sexually through use of seeds that have a single cotyledon, however a great number of monocots reproduce asexually through clonal propagation. Breeding systems that utilize self-incompatibility are much more common than those that utilize self-compatibility. The majority of monocots are animal pollinated (zoophilous), of which most are pollinator generalists. Monocots have mechanisms to promote or suppress cross-fertilization (allogamy) and self-fertilization (autogamy or geitonogamy). The pollination syndromes of monocots can be quite distinct; they include having flower parts in multiples of three, adaptations to pollination by water (hydrogamy), and pollination by sexual deception in orchids.

Pollen-presenter

A pollen-presenter is an area on the tip of the style in flowers of plants of the family Proteaceae on which the anthers release their pollen prior to anthesis. To ensure pollination, the style grows during anthesis, sticking out the pollen-presenter prominently, and so ensuring that the pollen easily contacts the bodies of potential pollination vectors such as bees, birds and nectarivorous mammals. The systematic depositing of pollen on the tip of the style implies the plants have some strategy to avoid excessive self-pollination.

Pollination

Pollination is the transfer of pollen from a male part of a plant to a female part of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents are animals such as insects, birds, and bats; water; wind; and even plants themselves, 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 has landed on the stigma, it develops a pollen tube which grows down the style until it reaches an ovary. Sperm cells from the pollen grain then move along the pollen tube, enter an ovum cell through the micropyle and fertilise it, resulting in the production of a seed.

A successful angiosperm pollen grain (gametophyte) containing the male gametes is transported to the stigma, where it germinates and its pollen tube grows down the style to the ovary. Its two gametes travel down the tube to where the gametophyte(s) containing the female gametes are held within the carpel. One nucleus fuses with the polar bodies to produce the endosperm tissues, and the other with the ovule to produce the embryo Hence the term: "double fertilization".

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 fertilization 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 brings together 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 fertilization: the result of pollination. The study of pollination by insects is known as anthecology.

Siegerrebe

Siegerrebe (literally "Victory vine" in German) is a white wine grape that is grown primarily in Germany with some plantings in England,Vancouver Island, Washington State, British Columbia's North Okanagan and Fraser Valley and Nova Scotia's Annapolis Valley. Siegerrebe was created by German viticulturalist Dr. Georg Scheu (1879-1949) in 1929 at a grape-breeding institute in Alzey in Rheinhessen, by crossing Madeleine Angevine and Gewürztraminer. However, Georg Scheu's son Heinz Scheu has claimed in a book that Siegerrebe was the result of self-pollination of Madeleine Angevine. Siegerrebe received varietal protection and was released for general cultivation in Germany in 1958.In 2006, there were 110 hectares (270 acres) of Siegerrebe in Germany with a decreasing trend, in similarity with other "new breeds" of white varieties. In Belgium, it is authorised for all still wine AOCs : Côtes de Sambre et Meuse, Hageland, Haspengouw, et Heuvelland.

Tinantia pringlei

Tinantia pringlei, sometimes known as the Mexican wandering Jew, is a perennial alpine plant in the dayflower family native to northeastern Mexico. The species is grown as an ornamental plant in temperate areas for its attractive spotted purple foliage and lavender flowers. It is also a common weed of greenhouses. The plants reproduce primarily or exclusively through self-pollination.

Trachycarpus

Trachycarpus is a genus of eleven species of palms native to Asia, from the Himalaya east to eastern China. They are fan palms (subfamily Coryphoideae), with the leaves with a bare petiole terminating in a rounded fan of numerous leaflets. The leaf bases produce persistent fibres that often give the trunk a characteristic hairy appearance. All species are dioecious, with male and female flowers produced on separate plants although female plants will sometimes produce male flowers, allowing occasional self-pollination.

Xenogamy

Xenogamy (Greek xenos=stranger, gamos=marriage) is the transfer of pollen grains from the anther to the stigma of a different plant. This is the only type of pollination which during pollination brings genetically different types of pollen grains to the stigma.The term xenogamy (along with geitonogamy and autogamy) was first suggested by Kerner in 1876.

Cross-pollination involves the transfer of pollen grains from the flower of one plant to the stigma of the flower of another plant.

The main characteristics which facilitate cross-pollination are:

Herkogamy: Flowers possess some mechanical barrier on their stigmatic surface to avoid self-pollination, e.g. presence of gynostegium and pollinia in Calotropis.

Dichogamy: Pollen and stigma of the flower mature at different times to avoid self-pollination.

Self-incompatibility: In same plants, the mature pollen fall on the receptive stigma of the same flower but fail to bring about self-pollination.

Male sterility: The pollen grains of some plants are not functional. Such plants set seeds only after cross-pollination.

Dioecism: Cross-pollination always occurs when the plants are unisexual and dioecious, i.e., male and female flowers occur on separate plants, e.g., papaya, some cucurbits, etc.

Heterostyly: The flowers of some plants have different lengths of stamens and styles so that self-pollination is not possible, e.g., Primula, Linum, etc.

Languages

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