Papaya: Origin and Botany

Papaya (Carica papaya L.) is a popular fruit native to tropical America. It is usually grown for its small to large melon-like fruit. It is a herbaceous perennial, bearing fruit continuously at the leaf axils spirally arranged along the single erect trunk. The papaya is also called papaw, pawpaw, papayer (French), melonenbaum (German), lechosa (Spanish), mamao, mamoeiro (Portuguese), mugua (Chinese) and betik (Malaysian, Indonesian).

BOTANY
Taxonomy and nomenclature
The cultivated papaya belongs to the family Caricaceae and is the only member of the genus Carica. Caricaceae is a small family of dicotyledonous plants with six genera; four of tropical American origin (Carica, Jarilla, Jacaratia, Vasconcella) and one, Cylicomorpha, from equatorial Africa. Caricaceae species have been variously classified in families such as Cucurbitaceae, Passifloraceae, Bixaceae and Papayaceae. Approximately 71 species have been described, though Badillo (1993, 2000) reduced the number to 32 species, with the  following distribution: Carica, 1 species, Cylicomorpha, 2 species, Jacaratia, 5 species, Jarilla, 3 species, Vasconcella, 20 species, and Horovitzia, 1 species. Papaya (C. papaya L.) is the most important economic species in Caricaceae. Carica and Vasconcella species are dioecious, except for the monoecious Vasconcella monoica (Desf.) and some Vasconcella pubescens and the polygamous C. papaya. Most species are herbaceous, single-stemmed and erect. Other than C. papaya L., the other edible species are Vasconcella candamarcensis Hook. f., V. monoica Desf., Vasconcella erythrocarpa Heilborn, Vasconcella goudotiana Solms- Laubach and Vasconcella quercifolia Benth. and Hook (Storey, 1969). These fruit are mostly eaten cooked, being normally dry and lacking the juicy flesh of C. papaya. Another edible species, Vasconcella pentagona, is called ‘babaco’.

Origin and distribution
C. papaya has not been found wild in nature and is only distantly related to the Vasconcella species, based upon isozyme and AFLP analysis. The greatest diversity in C. papaya exists in the Yucatan–San Ignacio–Peter–Rio Motagua area of Central America. The volunteer population in this area has greater diversity than domesticated populations (Morshidi, 1996; Van Droogenbroeck et al., 2002). Papaya origins are rather uncertain, but there is some agreement among botanists that it originated in the lowlands of Central America, between southern Mexico and Nicaragua. Early distribution over a wide geographical region in Central and South America was aided by the abundance of seeds in the fruit and the seeds long viability. The accounts of 18th-century travellers and botanists indicated that seeds of papaya had been taken from the Caribbean to Malacca and on to India (Storey, 1941a). From Malacca or the Philippines, distribution continued throughout Asia and to the South Pacific region. Don Francisco Marín, a Spanish explorer and horticulturist, is credited with the introduction of papaya into Hawaii from the Marquesas Islands during the early 1800s. Papaya is now grown in all tropical countries and in many subtropical regions of the world (Anonymous, 2003).

Papaya fruit fly

Species name	Bactrocera papayae
What does it look like?	The Asian papaya fruit fly is about the same length as a common housefly but more slender. It grows to 7 mm in length and has clear wings, generally black chest and a paler abdomen with a distinctive black T-shaped marking on the back. The Queensland fruit fly, by comparison, is much the same size but is an overall reddish-brown colour. An expert eye is needed to identify papaya fruit fly under a microscope.
Where does it occur?	Papaya fruit fly is endemic in Thailand, Malaysia, Borneo, Indonesia and Singapore. It has been present in Papua New Guinea since 1992. In March 1993, it was detected for the first time in Australian territory on the islands of Saibai, Boigu and Dauan, adjacent to the Papua New Guinea coast; and on Stephen and Darnley Islands close to the centre of Torres Strait. Papaya fruit fly moves into the Torres Strait with the monsoonal winds each wet season and is eradicated annually as part of a proactive containment strategy administered by Biosecurity Queensland and the Australian Quarantine and Inspection Service. In October 1995, the detection of papaya fruit fly near Cairns initiated a major eradication campaign. This pest was successfully eradicated from the Cairns region in 1998, but Biosecurity Queensland remains vigilant and maintains a surveillance and trapping program throughout the state to ensure early detection should the pest reach the mainland of Queensland again.
Symptoms and damage	What makes this pest such a problem is that it infests twice the number of fruit types as the Queensland fruit fly (209 compared with 116), many of them at a greener stage. As a result of the pest's heavy infestation habits, revised field control strategies would be needed should it become established in horticulture production regions. Earlier applications of spray regimes and more intensive or regular treatments will be required in some crops, because of the higher levels of damage papaya fruit fly can inflict and its tendency to attack some fruit at a greener stage. Many countries have trade restrictions on fruit that come from regions known to have papaya fruit fly. Should this exotic fruit fly species establish in Queensland, growers may face market access difficulties when exporting their produce.
Life cycle	Adult female flies lay their eggs just under the skin of fruit, depositing fruit decaying bacteria at the same time. Within one to two days, the eggs hatch into maggots (larvae) which feed on the decaying fruit, causing premature fruit drop. Considerable damage can occur inside the flesh before obvious signs of infestation can be seen on the fruit. The most obvious signs of infestation are small discoloured patches on the skin, which develop from punctures or stings made by the female as she lays her eggs. It takes 7-12 days for the larvae to leave the fruit to develop into pupae in the soil. Adults emerge from the pupae in another 10-14 days, and become sexually mature after one to two weeks. They live for several months and are capable of reproducing throughout their life span. Like most tropical fruit fly species, papaya fruit fly multiplies rapidly and can disperse over large distances. It is capable of establishing in any of the mainland states of Australia.
Surveillance	Biosecurity Queensland monitors a network of traps for papaya fruit fly in high-risk urban and remote centres in Queensland. The Australian Quarantine and Inspection Service is responsible for papaya fruit fly surveillance on each inhabited island in Torres Strait. Biosecurity Queensland acts quickly with well planned eradication strategies whenever papaya fruit fly is detected on Queensland territory. Early detection of this pest greatly enhances the likelihood that the pest could be eradicated again if it re-establishes in mainland Queensland.