Delayed Selfing – A mechanism providing reproductive assurance at a lower cost than autonomous selfing, when the anthers or stigma change position as the flower ages, bringing them into close proximity and promoting self- pollination. Reproductive Compensation – A result of more ovules than can mature into seeds, and the production of large numbers of seeds over the lifespan of a perennial plant, can contribute to the evolution of mixed mating systems. Rare selfed seedlings with higher fitness may decrease the fitness difference between selfed and out-crossed offspring. Cleistogamy – Most plants producing cleistogamous (closed, selfing) flowers also produce chasmogamous (open, outcrossing) flowers, and consequently will typically produce mixtures of selfed and out-crossed seeds.
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Faster pollen tube growth rate in Dalechampia scandens results in reduced inbreeding depression in mixed-mating systems due to intense pollen competition after self-pollination. Gametophytic selection was apparently responsible for increased seed mass and radicle growth in selfed seedlings.
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Ulmus 'Lobel' is a Dutch hybrid cultivar raised at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen, from a crossing of clone '202' ('Exoniensis' × U. wallichiana) with '336' ('Bea Schwarz', selfed). 'Lobel' was cloned in 1962 and released for sale in 1973.
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Ulmus 'Clusius' is a Dutch hybrid elm cultivar raised at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen, and released to commerce in 1983. 'Clusius' was derived from a crossing of the same Dutch clones that produced the fastigiate 'Lobel' released in 1973: '202' ('Exoniensis' × U. wallichiana) and '336' ('Bea Schwarz' selfed).
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Macrostomum hystrix prefers outbreeding if partners are available because selfing also has costs. The amount of offspring of worms that selfed is reduced, as is the offspring's survival. As a consequence, Macrostomum hystrix only begins selfing in the extended absence of mating partners: delayed selfing represents a conditional reproductive strategy which allows them to deal with periodic conditions of low mate abundance.
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Ulmus 'Nanguen' (selling name ) is a complex fourth generation Dutch hybrid cultivar raised at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen. was derived from the cross 'Plantyn' × ('Bea Schwarz' selfed), an ancestry comprising four field elms (U. minor), a wych elm (U. glabra), the curious Exeter Elm ('Exoniensis'), and a frost-resistant selection of the Himalayan elm (U. wallichiana).
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Cuttings were taken in 1915, although all but one of the resultant trees have also died, the survivor still thrives (2006) at Barclay Beach. Moreover, a specimen raised from seed survives on Founder's Green, Haverford College, and is perpetuated by selfed seedlings gathered by the arboretum staff in autumn. The tree is not known to be in cultivation beyond North America, nor is it in commerce.
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The Dutch hybrid cultivar Ulmus 'Dodoens' was derived from a selfed seedling of a crossing of the Exeter Elm Ulmus 'Exoniensis' with the Himalayan Elm Ulmus wallichiana at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen. The tree was one of several cultivars prepared for release in 1970, but delayed by the outbreak of the second, far more aggressive strain of Dutch elm disease.
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Morning glory vines spread their vegetation and flowers reproduce via mixed mating systems. Peanut plants utilize mixed mating systems, often with cleistogamous flowers. A mixed mating system (in plants), also known as “variable inbreeding” a characteristic of many hermaphroditic seed plants, where more than one means of mating is used. Mixed mating usually refers to the production of a mixture of self-fertilized (selfed) and outbred (outcrossed) seeds.
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U. wallichiana was crossed with the Exeter elm 'Exoniensis' in the Netherlands in 1938, from which progeny was selected clone '202', destined to become a fundamental component of the Dutch elm breeding programme in the 1960s and 1970s. Selfed or hybridized with U. minor or earlier Dutch hybrids, its progeny include 'Clusius', 'Dodoens', 'Lobel', and 'Plantyn'. 'Plantyn' was in turn to play a vital part in the third generation of Dutch hybrids; two selfed specimens were selected and released as 'Columella' and, much later, 'Wanoux' = , while 'Plantyn' itself was crossed with U. 'Bea Schwarz' to create 'Nanguen' = , arguably the most successful Dutch elm cultivar released to date. 'Plantyn' was also selected for use in the Italian elm breeding programme that started in the 1970s, and was crossed with varieties of the Siberian elm U. pumila to create a number of hardy trees renowned for their rapid upright growth: 'Arno', 'Plinio', and 'San Zanobi'.
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Ulmus 'Columella' is a Dutch elm cultivar raised by the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen, from a selfed or openly pollinated seedling of the hybrid clone 'Plantyn' sown in 1967. It was released for sale in 1989 after proving extremely resistant to Dutch elm disease following inoculation with unnaturally high doses of the pathogen, Ophiostoma novo-ulmi. However, propagated by grafting onto Wych Elm rootstocks, graft failure owing to incompatibility has become a common occurrence in the Netherlands.
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Historically, Charles Darwin's experiments on selfing and out-crossing many plant species caused him to question any adaptive value of self-fertilization. Early evolutionary models assumed inbreeding depression did not change, which increased the likelihood of stable mixed mating. Ronald Fisher (1941) presented the idea that selfing plants had a genetic transmission advantage over outcrossing plants because selfed offspring would inherit two copies of the seed parent's genome instead of just one. His models solidified the idea of automatic selection for increased selfing.
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The pendant flowers prevent pollination by Lepidoptera. In N. albimarginatus there may be either a long stigma with short and mid length anthers or a short stigma and long anthers (dimorphism). In N. triandrus there are three patterns of sexual organs (trimophism) but all have long upper anthers but vary in stigma position and the length of the lower anthers. Allogamy (outcrossing) on the whole is enforced through a late-acting (ovarian) self-incompatibility system, but some species such as N. dubius and N. longispathus are self-compatible producing mixtures of selfed and outcrossed seeds.
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David Lloyd (1979) developed phenotypic a model that showed that the conditions of automatic selection for selfing via pollinators was different from autonomous selfing, and predictive of stable mixed mating systems. Lande & Schemske (1985) introduced the idea that inbreeding depression, is not constant and evolves through purging of genetic load due to selection associated with selfing. They predicted that outcrossing as a mating strategy would resist increases in selfing frequencies due to inbreeding depression, but once inbreeding depression was reduced, selection due to the genetic transmission advantage would result in the production of only selfed seeds. Their model predicted that most plants would either be outcrossing or selfing.
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Mass Action Model – Holsinger's “mass action” model assumes that the proportion of selfed and out-crossed seeds produced is a function of rates of pollen transfer among plants and plant density. This model predicts that mixed mating can be a stable strategy when plants receive mixtures of self and out-cross pollen. Selective Interference –The genetic process of selective inference may prevent purging of genetic load and counterbalance the automatic selection of selfing. Cryptic Self- Incompatibility – A mechanism of reproductive assurance, pollen competition favors out-cross pollen resulting in complete out-crossing when pollinators are abundant, but allows for self-fertilization when pollen is limited.
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Just before anthesis, the anthers release their pollen, depositing it onto the stigma, which in many cases has an enlarged fleshy area specifically for the deposition of its own pollen. Nectar-feeders are unlikely to come into contact with the anthers themselves, but can hardly avoid contacting the stigma; thus, the stigma functions as a pollen-presenter, ensuring the nectar-feeders act as pollinators. The downside of this pollination strategy is that the probability of self-fertilisation is greatly increased; many Proteaceae counter this with strategies such as protandry, self-incompatibility, or preferential abortion of selfed seed. The systems for presenting pollen are usually highly diverse, corresponding to the diversification of the pollinators.
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However, as opposed to 'complete' or 'absolute' SI, in CSI, self-pollination without the presence of competing cross pollen, results in successive fertilization and seed set; in this way, reproduction is assured, even in the absence of cross-pollination. CSI acts, at least in some species, at the stage of pollen tube elongation, and leads to faster elongation of cross pollen tubes, relative to self pollen tubes. The cellular and molecular mechanisms of CSI have not been described. The strength of a CSI response can be defined, as the ratio of crossed to selfed ovules, formed when equal amounts of cross and self pollen, are placed upon the stigma; in the taxa described up to this day, this ratio ranges between 3.2 and 11.5.
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As plants pursue reproductive assurance through self-fertilization, there is an increase in homozygosity , and inbreeding depression, due to genetic load, which results in reduced fitness of selfed offspring. Solely outcrossing plants may not be successful colonizers of new regions due to lack of other plants to outcross with, so colonizing species are expected to have mechanisms of reproductive assurance - an idea first proposed by Herbert Baker and referred to as Baker's Law. Baker’s Law predicts that reproductive assurance should be common in weedy plants that persist by colonizing new sites. As plants evolve towards increase self-fertilization, energy is redirected to seed production rather than characteristics that increased outcrossing, such as floral attractants, which is a condition known as the selfing syndrome.
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Cultivars come in shades of yellow, orange, salmon, rose, pink, cream and white as well as bi-colored varieties. Seed strains include: ‘Champagne Bubbles’ (15-inch plants in orange, pink, scarlet, apricot, yellow, and creamy-white); ‘Wonderland’ (10-inch dwarf strain with flowers up to 4 inches wide); ‘Flamenco’ (pink shades, bordered white, 1½ to 2 feet tall); ‘Party Fun’ (to 1 foot, said to bloom reliably the first year in autumn and the second spring); ‘Illumination’ and ‘Meadow Pastels’ (to 2 feet, perhaps the tallest strains); ‘Matador’ (scarlet flowers to 5 inches across on 16 inch plants); the perennial 'Victory Giants' with red petals and ‘Oregon Rainbows’, which has large selfed, bicolor, and picoteed flowers and is perhaps the best strain for the cool Pacific NorthwestSunset Publishing (2001) Sunset Western Garden Book, ed. 7 (Sunset Books Incorporated: ) (elsewhere this strain’s buds frequently fail to open). The dwarf Gartenzwerg group, and the cultivars ‘Solar Fire Orange’ and ‘Summer Breeze Orange’ have all won the Royal Horticultural Society’s Award of Garden Merit.
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