APOMIXIS HERRAMIENTA PODEROSA PARA EL MEJORAMIENTO *Consiste en la formación de semillas que contienen embriones. Apomixis importance is widespread among tropical grasses: Bothriochloa, Bouteloua, cultivos como mango, cítricos, manzanos y diversas. Os porta-enxertos de cítricos são essenciais na cultura de citros porque .. The aim is to edit the orthologues of apomixis candidate genes in.
|Published (Last):||26 December 2018|
|PDF File Size:||8.70 Mb|
|ePub File Size:||10.10 Mb|
|Price:||Free* [*Free Regsitration Required]|
Citrus taxonomy refers to the botanical classification of the speciesvarietiescultivarsand graft hybrids within the genus Citrus and related genera, found in cultivation and in the wild. Citrus taxonomy is complex. Some are only selections of the original wild types, while others are hybrids between two or citricod ancestors. Citrus plants hybridize easily between species with completely different morphologies, and similar-looking citrus fruits may have quite different ancestries.
Detailed genomic analysis of wild and domesticated citrus cultivars has suggested that the progenitor of modern citrus species expanded out of the Himalayan foothills in a rapid radiation that has produced at least 10 wild species in South and East Asia and Australia. A;omixis commercial cultivars are the product of hybridization among these wild species, with most coming from crosses involving citronsmandarins and pomelos.
Most hybrids express different ancestral traits when planted from seeds F2 hybrids and can continue a stable lineage only through vegetative propagation. Some hybrids do reproduce true to type via nucellar seeds in a process called apomixis. All of the wild ‘pure’ citrus species trace apomuxis a common ancestor that lived in the Himalayan apomixie, where a late- Miocene citrus fossil, Citrus linczangensishas been found.
At that time, a lessening of the monsoons and resultant drier climate in the region allowed the citricls ancestor to expand across south and east Asia in a rapid genetic radiation. After the plant crossed the Wallace line a second radiation took place in the early Pliocene about 4 million years ago to give rise to the Australian species.
Most modern cultivars are actually e derived from a small number of ‘pure’ original species. Though hundreds of species names have been assigned, a recent genomic study by Wu, et al.
Of these, seven were native to Asia: In Australia three were identified: Many other cultivars previously identified as species were found to be aoomixis related variants subspecies or varieties or hybrids of these species,  though not all cultivars were evaluated. Interbreeding seems possible between all citrus plants, and between citrus plants and some plants which may or may not be categorized as citrus.
The ability of citrus hybrids to self-pollinate and to reproduce sexually also helps create new varieties. The three predominant ancestral citrus taxa are aopmixis C. However, some of these hybrids have interbred with one another and with the original taxa, making the citrus family tree a complicated network.
Kumquats do not naturally interbreed with core taxa due to different flowering times,  but hybrids such as the calamondin exist. Australian limes are native to Australia and Papua New Guineaso they did not naturally interbreed with the core taxa, but they have been crossbred with mandarins and calamondins by modern breeders. Humans have deliberately bred new citrus fruits by propagating seedlings of spontaneous crosses e.
Meyer lemonand crossing different varieties e. Initially, many citrus types were identified and named by individual taxonomists, resulting in a large number of identified species: His Citrus he likewise subdivided into two subgenera: The Swingle system is generally followed today with much modification; however, there are still large differences in nomenclature between countries and individual scientists.
Phylogenetic analysis confirms the hybrid origin of most citrus cultivars, indicating a small number of founder species. While the subgenera suggested by Tanaka proved similar to the phylogenetic divisions, Swingle’s ciitricos were polyphyletic and hence do not represent valid taxonomy. Historical genera are also dubious.
Kumquats had been placed in a separate genus Fortunellawhile two genera were suggested by Swingle for the Australian limes, Microcitrus and Eremocitrus.
However, genomic analysis has pointed to these groups nesting within the phylogenetic tree of the other citrus plants. Since their placement in distinct genera would make Citrus a paraphyletic grouping, it has been suggested that all of these are correctly members of a single genus, Citrus. Most commercial varieties are descended from one or more of the ‘core species’, citronsmandarinsand pomeloswhich share in common a complex floral anatomy that gives rise to more complex fruit.
These core species, and to a lesser extent other citrus, have given rise to a wide variety of hybrids for which the naming is inconsistent.
The same common names may be given to different species, citrus hybrids or mutations. For example, citrus with green fruit tend to be spomixis ‘limes’ independent of their origin: Australian limes, Musk limesKey limeskaffir limesRangpur limessweet limes and wild limes are all e distinct. Fruit with similar ancestry may be quite different in name and traits e. Many traditional citrus groups, such as true sweet oranges and lemons, seem to be bud sportsclonal families of cultivars that have arisen from distinct spontaneous mutations of a single hybrid ancestor.
Mandarin oranges tangerines, satsumas – Citrus reticulata are one of the basic species, but the name mandarin is also used more generally for all small, easily peeled citrus, including a large range of hybrids. Webber divided them into four groups, king, satsuma, mandarin, and tangerine, and Citticos saw in them four species.
All characterized varieties commercially called mandarins are actually hybrids. In addition to genetically pure mandarins, a second type are the result of hybridization with pomelos followed by subsequent backcrossing with mandarins to retain only a few pomelo traits. The third citricod arose more recently from the crossing of these hybrids again with pomelos or sweet oranges which are themselves crosses of hybrid mandarins and pomelos. This produces mandarins with more, longer stretches of pomelo DNA.
Mangshan wild mandarin C.
Citrus taxonomy – Wikipedia
In a limited genomic analysis, Feroniella was surprisingly found to cluster with C. The pomelo Citrus maximaa second of the core species from which most citrus hybrids have derived, is native to southeast Asia. Varieties of true non-hybrid Citron Citrus medica have distinctly different forms.
The citron usually propagates by cleistogamya self-pollination within an unopened flower, and this results in the lowest levels of hetero zygosity among the citrus species. Many citron varieties were proven to be non-hybrids despite their rather dramatic morphological differences;       however, the florentine citron is probably of hybrid origin.
Genetic analysis of citrons has shown that they divide into three citircos. One cluster consists of wild citrons that originated in China and produce non-fingered fruit with pulp and seeds. A second cluster, also native to China, consist of the fingered citrons, most of which are seedless and must be propagated artificially. The third cluster represents the Mediterranean citrons, thought to have originally been introduced there from India.
Some fingered citron varieties are used in buddhist offerings ctiricos, and some more common varieties are used as the etrog in the Jewish harvest festival of Sukkot.
There is also a specific variety of citron called etrog. The Mountain citron is a complex citrus hybrid that only includes trace amounts of true citron. Kumquats are a separate species, with few hybrids. Carl Peter Thunberg originally classified the kumquats as Citrus japonica in his book, Flora Japonica.
In citircos, Swingle reclassified them in a separate genus, Fortunellanamed in honor of Robert Fortune. Seven species of Fortunella were generally recognized— F. Since the kumquat is a cold hardy speciesthere are many hybrids between common citrus members and the kumquat.
Subsequent study of the many commercial citrus lineages revealed such complexity that the genera could not be separated,  and genomic analysis rooted Fortunella within the polyphyletic tree of Citrus. The Flora of China unites all kumquats as the single species, Citrus japonica. Swingle coined the Citrus subgenus Papeda to separate its members from the more edible citrus, that also differ from other citrus in that its stamens grow separately, not united at the base.
Since the latter two species locate to different branches of the citrus phylogenetic tree, the group would be polyphyletic and not a valid division. Australian and New Guinean citrus species had citrico viewed as belonging to separate genera by Swingle, who placed in Microcitrus all but the desert lime, for which he used Eremocitrus. However, genomic analysis shows that though they form em distinct clade from other citrus, this is nested within the citrus phylogenetic tree, most closely related to kumquats, suggesting that all these species should be included in the genus Citrus.
Clymeniawill hybridize with kumquats and some limes. Citrus hybrids include many varieties and species that have been selected by plant breeders. This is done not only for the useful characteristics of the fruit, but also for plant size and growth characteristics apomixsi as cold-tolerance. Some citrus hybrids occurred naturally, and others have been deliberately created, either by cross pollination and selection among the progeny, or rarely, and only recently as somatic hybrids.
The aim of plant breeding of hybrids is to use two or more different citrus varieties or species, in order to get traits intermediate between those of the parents, or to transfer individual desirable traits of one parent into the other. In some cases, particularly with the natural hybrids, it has been viewed as hybrid speciation and the new plants have been viewed as different species from any of their parents.
Styling a hybrid as such a cross between two species can present challenges. In some cases the parental species that gave rise to a hybrid have yet to be determined, while genotyping reveals some hybrids to descend from three or more ancestral species.
Hybrid taxonomy is inconsistent. There is disagreement over whether to assign species names to hybrids, and even modern hybrids of known parentage are sold under general names that give little information about their ancestry, or even give technically incorrect information. This can be a problem for those who can eat only some citrus varieties. Drug interactions with chemicals found in some citrus, including grapefruit and Seville oranges  make the ancestry of citrus fruit of interest; many commonly sold citrus varieties are grapefruit hybrids   or pomelo -descended grapefruit relatives.
One medical review has advised patients on medication to avoid all citrus juice,  although some citrus fruits contain no furanocoumarins. The most common citrus hybrids that are sometimes treated as a species by themselves, especially in folk taxonomyare:.
All of these hybrids have in turn been bred back with their parent stocks or with other pure or hybrid citrus to form a broad array of fruits. Naming of these is inconsistent, with some bearing a variant of the name of one of the parents or simply another citrus with superficially-similar fruit, a distinct name, or a portmanteau of ancestral species.
While most other citrus are diploidmany of the Key lime hybrid progeny have unusual chromosome numbers. For example, the Persian lime is triploidderiving from a diploid Key lime gamete and a haploid lemon ovule. A second group of Key lime hybrids, including the Tanepao lime and Madagascar lemon, are also triploid but instead seem to have arisen from a backcross of a diploid Key lime ovule with a citron haploid gamete.
The ‘Giant Key lime’ owes its increased size to a spontaneous duplication of the entire diploid Key lime genome to produce a tetraploid. Historically, hybrids with similar characteristics have been placed together in a number of hybrid species, yet relatively recent genomic analysis has revealed some hybrids assigned to the same species to be of quite distinct ancestry. No alternative system of grouping fruit in hybrid species has been adopted.
While most citrus hybrids derive from the three core species, hybrids have also been derived from the micranthathe Ichang papeda and the kumquat. The best known hybrid from micrantha is the Key lime or Mexican limederived from the breeding of a male citron and a female micrantha. For example, the Indian wild orangeonce suggested as a possible ancestor of today’s cultivated citrus fruits,  yielded conflicting phylogenetic placements in more limited genetic analysis,   but study of nuclear markers and chloroplast DNA showed it to be of maternal citron lineage, with further genetic contributions from mandarin and papeda.
A large group of commercial hybrids involve the kumquatFortunella in the Swingle system. Citrofortunella was coined as a genus containing intergeneric hybrids between members of the Citrus and the Fortunellaand is named after its parent genera. With the placement of kumquats within CitrusCitrofortunella are no longer viewed as being intergeneric hybrids. All likewise belong in Citruswhile Citrofortunella as a distinct genus name would no longer be valid.