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A wealth of plant species used by papah for different purposes, but mainly as food, originated and domesticated in the Mesoamerican region. Papaya Carica papaya is the third most cultivated tropical crop worldwide, and it has been hypothesized that Mesoamerica is the most likely center of its origin and domestication. In support of it, many wild sez of papaya occur throughout Mesoamerica and hence represent the gene pool of genetic variability for further evolution and future crop management.

Despite its importance, a dearth of information exists regarding the status of wild populations of papaya, as compared to the extent of knowledge, and interest, on domesticated varieties.

We review the evidence on the extant wild populations of papaya, as well as its origin and distribution. Also, we synthetize what is known on the domestication history of the species, including the domestication syndrome that distinguishes wild and domesticated papayas. Moreover, we make an account of the use of genetic markers to assess genetic diversity of wild and domesticated papaya, and discuss the importance of papaya as the first species with a transgenic cultivar to be released for human consumption, and one that has its complete genome sequenced.

Evidence from different disciplines strongly suggest that papay originated and was domesticated in Mesoamerica, and that wild populations in the region possess, still, high genetic diversity compared to the domesticated papaya. Se, we outline papaya as an excellent model species for genomic studies that will help gain insight into the domestication process and improvement of papaya and other tropical crops.

Papaya Carica papaya L. Carica papaya is a member of the Caricaceae family and is the most economically important species in the family Carvalho and Renner, The Caricaceae family originated in Africa where two extant species occur. The dispersal to Central America from Africa occurred ca.

It is estimated that C. Carica papaya produces huge palmate-shaped leaves. Female flowers are produced at the axils of the leaf petiole, and later the fruits will occupy that position along the stem.

Male individuals produce inflorescences. Three sex types of papaya papag known: female, male, and hermaphrodite trees. Cultivars can inbred, resulting in stable characteristics across generations Manshardt, For gynodioecious cultivated papaya, it has been reported that two-thirds of the plants correspond to hermaphrodites and one-third to female plants, though dioecious cultivars exist VanBuren et al.

Sex determination for the three papay of papaya, female, male, and hermaphrodite plants, is genetically regulated by the pairing of sex chromosomes Carvalho and Renner,through a sex-linked region that behaves like an XY sex chromosome. For male and hermaphrodite individuals, sex is controlled by slightly different Y chromosome regions: Y h in hermaphrodites and Y in males VanBuren et al.

Female plants produce flowers and fruits all year round in tropical regions; however, in subtropical areas, despite continuous flowering, fruit set is decreased during drier seasons Gonsalves, Papaya is the third most cultivated tropical crop world-wide, Brazil and India are the largest producers of papaya although Mexico is the main exporter Evans and Ballen, Under cultivation paoay trees grow fast, producing mature fruits within 9—12 months after planting.

Commercially, a density of 1,—2, trees per hectare, can produce fromtolbs per hectare, per year Gonsalves, Among common fruits, papaya is ranked first on nutritional scores for the percentage of vitamin A, vitamin Papay, potassium, folate, niacin, thiamine, riboflavin, iron and calcium, and fiber Huerta-Ocampo et al. Moreover, fruits, stems, leaves and roots of papaya are used in a wide range of sex applications and papain production Ming et al.

Commercial production of papain is directed for protein digestion, mainly as a red meat tenderizer, for the brewing of beer, and the skin treatment of warts and scars Ming et al.

Because of its rapid growth, continuous harvest and multiple ppaay, papaya is widely common in home gardens of tropical regions Manshardt, Two main differences in flower morphology and fruit size distinguish wild and domesticated papayas; wild papayas bear either male or female flowers i. Carica papaya is mainly pollinated by sphingid moths Vega-Frutis and Guevara, and skippers.

Figure 1. A Wild female papaya tree with fruits in Yucatan, Mexico. B Wild population of Carica papaya in Yucatan, Eex.

C Wild fruits, intermediate form fruits possible hybrid between wild and domesticated plantsand domesticated papaya fruit Maradol variety. Since wild C. Moreover, because papaya is one of the most economically important tropical crops in the world, and wild populations still occur naturally, the species represents an ideal system to study, in depth, the process of domestication.

Here, we present a review of the existent knowledge on the origin, distribution and domestication of papaya, and discuss the usage of genetic and genomic methods to study the domestication of this valuable species. Different authors suggest a Mesoamerican origin of C. One reason for the lack of archaeological data is the difficulty to identify papay from palay, and their pollen grains have been hardly found Carvalho and Renner, Phylogenetic evidence of the Caricaceae family, also supports a Mesoamerican origin of papaya.

Carvalho and Renner obtained a molecular phylogeny of sex Caricaceae family using chloroplast and nuclear data 4, bp of the 34 species in the family.

This is the only phylogeny using members from all the Caricaceae family. Their resulting phylogeny points that Carica papaya is more closely related to the genus Horovitziaendemic to Mexico, and Jarillaendemic to Mexico and Guatemala, than to the South American genus Vasconcelleaas previously thought Carvalho and Renner, Moreover, Carica, Jarilla and Horovitzia show an unilocular ovary, whereas the remaining South American Caricaceae possess 5-locular ovaries Carvalho and Renner, Sex morphological synapomorphy supports the family phylogeny.

Further evidence is offered by the origin of the Y h chromosome in cultivated hermaphrodite individuals of papaya VanBuren et al. By sequencing the entire male-specific region of the Y chromosome and comparing it with the previous sequences of the hermaphrodite-specific region of the Y h chromosome, Wang et al.

This reduced variability is consistent with a genetic bottleneck scenario sx brought about by domestication, and suggests that dioecy is ancestral in C. Given the ubiquity of dioecy in wild populations of papaya in Mesoamerica, an origin for the species in this region is a more parsimonious hypothesis.

Yet, genomic studies can aid to determine the origin of some innovations related with domestication. High values of genetic variation of wild populations, and wild relatives, are expected to be found in the centers of origin of crop species Gepts and Papa, Additionally, domestication is expected to reduce genetic diversity and provoke selective sweeps in genes associated to characters target of domestication Purugganan and Fuller, The higher genetic diversity was found in locations of southern Mexico, suggesting this region as a genetic reservoir for xex species see below.

Summing up, evidence strongly suggests papwy C. Regarding the natural distribution of papaya, this has been suggested to range from the northern tropical limit of Mexico to Costa Rica in Central America Aradhya et al. However, the precise assessment of its natural distribution is still lacking. One reason for this sez the scarcity of studies in wild populations of papaya, and the paucity of herbarium specimens indicating whether a specimen belongs to a cultivated or wild individual.

Although they did not distinguish between wild and cultivated plants, their results show that most specimens belong to Mexico and to a lesser extent to Central America Unfortunately, the present rates of deforestation and habitat fragmentation within the proposed distribution range of wild papaya is high enough as to endanger the persistence of plant species Papay et al.

This, coupled with the lack of information on the state of many wild varieties of important crop species, warn us about the relevance of studying and conserving wild populations and wild relatives of papaya and other crop species. The limited occurrence of wild populations of C. Mesoamerica is considered as one of the World's centers of plant domestication Harlan, ; Pohl et al. The Maya was the most important culture present in that region before the conquest of Mexico by Spain in the sixteenth century, and probably one of the first to cultivate and trade the fruits of C.

By sex time of the conquest of Mexico, it is believed that papaya was cultivated by native people all the way from southern Mexico to the Isthmus of Panama, where it was locally known as olocoton Storey et al. In the sixteenth century the Spaniards were probably the first responsible for the spread of papaya beyond Mesoamerica Carvalho and Renner, It was introduced into the Hispaniola island nowadays Haiti and Santo Domingo in 1, There, it acquired the Carib Indian name ababaithat would then be changed to papaia, papia, papeyaand finally papaya.

In papaya was taken outside sex America to Indonesia, and then spread papay throughout the East Indies and tropical Asia Storey et al. After that, it rapidly spread into other Asian countries and finally to Africa, brought by European colonial powers, such as Portugal, Denmark, Great Britain and France Manshardt, Moreover, because the papaya seeds have a moderate period of papy, it is likely that this trait aided to its rapid spread paay the tropics, where it has existed practically since man has recorded modern history Schroeder, Nowadays, there are many varieties papay papaya cultivated in most tropical and subtropical regions of the world, differing in traits such as fruit size, color, flavour, and tree size Moore, The principal characters of papaya that have been studied as target of selection under domestication are: tree size, fruit size, sex types, and morphology, and germinability of seeds.

Whereas tree size has been selected to become smaller to facilitate fruit harvesting Niklas and Marler,selection has been focused on enlarging the fruit size and increasing the ovary sex pulp for human consumption Coppens d'Eeckenbrugge et al.

Papay a result, several varieties of papaya are cultivated around the world. Regarding sex types, in dioecious fruit crops, mutations inducing hermaphroditism have been associated with domestication; this is the case of species se strawberry, grape and papaya Janick, In the Caricaceae family, dioecy is the ancestral stateand it has been suggested that hermaphrodite individuals in papaya, resulted from a natural mutation in male plants and were likely papay by humans for its favorable fruit phenotype Ueno et al.

Although crop plant domestication in Mesoamerica occurred around 6, years ago, the estimation coincides with the rise sex the Maya civilization.

Given that hermaphrodite individuals are rarely found in wild populations of Mesoamerica, this strongly supports that papaya was domesticated by the Mayans or other Mesoamerican cultures thousands of years ago. Finally, seeds from wild and domesticated papayas differ in size, oapay rate, dormancy, and light sensitivity.

This domestication syndrome has been reported for other crops Doebley et al. Understanding crop domestication is crucial to fulfill the demand for improving yield and quality of crops Tang et al.

Knowledge of the genetic diversity within crop species dex essential to understand their origin, domestication and evolutionary relationships, and to efficiently develop strategies for the conservation of their genetic resources, and effective crop improvement Moore, Furthermore, crops represent excellent systems for the study of rapid evolution.

For the case of papaya, the species now represents an important model in genetic and genomic studies; papaya is one of the first plant sex to have its genome sequenced Ming et al.

In this section, we briefly review some advances of genetic and oapay methods in papaya; from what swx known about the state of wild populations, to recent advances in domesticated sex. It must be noted, however, that recent specialized reviews about genomics in papaya have been published elsewhere Ming et al. A recurrent consequence of domestication is the reduction of genetic diversity due to papat 2-fold effect of sex drift and selection that operate during the domestication process Doebley et w.

Early on, the use of genetics in tropical fruit crops was confined to the development of isozyme and dominant PCR-based markers and their use for germplasm diversity analysis and clonal fingerprinting; however, information from dominant markers is of limited use in ssx applications Litz and Padilla, Since then, codominant markers, known as simple sequence repeat SSR markers or microsatellites, have been developed for several tropical fruit crops and used for parentage analysis, clonal fingerprinting, genetic diversity analysis, and development of genetic linkage maps.

Nowadays, the increased capability of DNA sequencing by next generation methods, is leading to increased interest in tropical tree fruit crops and to new opportunities to increase the rate of genetic gain in breeding programs Litz and Padilla, Genetic knowledge of papaya has been accelerated with the advances in molecular markers, linkage and physical maps, comparative genomics studies, and the sequencing of its genome Tripathi et al.

For genetic diversity studies, some molecular markers have been developed for papaya, mainly SSRs Ocampo et al. However, most studies have focused on papay papaya, with a dearth of studies addressing the genetic diversity and structure of wild populations. Using both nuclear SSRs and chloroplast DNA markers in individuals of 19 natural populations, we found a mean observed heterozygosity of 0.

The area with the higher genetic diversity for both markers occur in southeast Mexico, near the region of the Tehuantepec Isthmus. Populations that inhabit forest fragments showed a reduced genetic diversity, higher population differentiation, and less migrants. Together, these studies suggest that wild papaya has maintained genetic connectivity among populations throughout time; however, populations are becoming recently structured dex due to human disturbances of its natural habitat, like habitat fragmentation, rendering important conservation concerns for the species in its wild form.

Efforts to conserve the natural genetic resources of the species should be addressed as well to assure the conservation of the domesticated varieties through genetic improvement.

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In general, there are three sex types in papaya: male, female and Somsri, S., M​. Jobin, R.A. Drew, W. Lawson and M.W. Graham. WHY PAPAYA MAY NOT BE THE BEST FRUIT FOR YOU: We all love papayas. Many love to have it empty stomach, add it to their salad or. Papaya (Carica papaya) is the third most cultivated tropical crop Three sex types of papaya are known: female, male, and hermaphrodite trees. Ocampo, J., d'Eeckenbrugge, G. C., Bruyère, S., de Bellaire, L. D. L., and.