<p style="text-align: justify;">The major producers of papaya are Brazil, Mexico, Nigeria, India, Indonesia, Ethiopia and the Democratic Republic of Congo. Papaya is grown primarily for the fresh market and processed food industry, and also has industrial applications.</p>

<p style="text-align: justify;">Papaya is a tropical fruit crop that is normally consumed fresh and is valued as a health food due to the high content of vitamins C and A. The pulp is eaten fresh, made into juice, preserves, and desserts. Immature pulp is used as a vegetable and in some regions young leaves are consumed like spinach. Papaya is used in traditional medicine with seed used as a vermifuge and leaves boiled for treatment against malaria, as examples. When the fruit is green and hard it is rich in white latex. As it ripens, it becomes light- or deep-yellow externally and the thick wall of succulent flesh becomes aromatic, yellow, orange or various shades of salmon or red. The dried latex, or milk, of immature fruit yields papain, a proteolytic enzyme similar in action to pepsin, which is used as a meat tenderizer, in breweries (to clarify beer), and in pharmacy. Papain is also used in bathing hides, degumming silk and softening wool.</p>

<p style="text-align: justify;">Hawaii, partly because of its distance from other papaya-growing areas, is less afflicted with disease problems than Florida and Puerto Rico, but still has to combat a number of major and minor maladies. Most serious of all is the papaya ringspot potyvirus (PRSV), which is common in Florida, Cuba, Puerto Rico, Trinidad, and first seen in Hawaii in 1959. It is transmitted mechanically or by the green peach aphid, <i>Myzus persicae</i>, and other aphids including the green citrus aphid, <i>Aphis spiraecola</i>, in Puerto Rico. Papaya plants infected by PRSV lose their photosynthetic capacity and as a result display stunted growth, deformed and inedible fruit, and eventually, plant mortality. When plants are infected at the early stages they will not produce mature fruit. If they are infected at a later stage, fruit production is reduced and of poor quality because of ringspots on the fruit and a decrease in sugar concentration. PRSV is very difficult to control and once a plant has become infected there is no remedy, but measures to avoid spread include the destruction of affected plants, control of aphids by pesticides, and elimination of all members of the Cucurbitaceae (alternate hosts for the virus) from the vicinity.</p>

<p style="text-align: justify;">Papaya lines 55-1 and 63-1 were developed using recombinant DNA techniques to resist infection by PRSV by inserting virus-derived sequences that encode the PRSV coat protein (CP). The introduced viral sequences do not result in the formation of any infectious particles, nor does their expression result in any disease pathology.</p>

<p style="text-align: justify;">These transgenic papayas exhibit &ldquo;pathogen-derived resistance&rdquo; to infection and subsequent disease caused by PRSV through a process that is related to viral cross-protection. Although the exact mechanism by which the viral protection occurs is unknown, most evidence suggests that expression of viral CP by a plant interferes with one of the first steps in viral replication, uncoating (removal of CP) from the incoming virus (Register &amp; Nelson, 1992). Other modes of action of cross-protection have also been suggested (Matthews, 1991).</p>

<p style="text-align: justify;">Papaya lines 55-1 and 63-1 were tested in field trials in the United States (1991&ndash;1996). These tests demonstrated that 55-1 and 63-1 plants exhibited the typical agronomic characteristics of conventional papaya varieties, with the addition of resistance to PRSV infection. Papaya lines 55-1 and 63-1 were comparable to conventional papaya varieties and did not exhibit weedy characteristics, and had no effect on nontarget organisms or the general environment.</p>

<p style="text-align: justify;">Papaya plants have different mating systems and may be either dioecious (male and female flowers are on separate plants) or gynodioecious (plants with perfect flowers/ hermaphrodite and plants with only female flowers). Commercial papaya lines are mostly gynodioecious as the hermaphroditic plants are generally self-pollinating. A low rate of out-crossing still occurs since the plants produce copious pollen during most of the year. The degree of cross-pollination among papaya varieties is dependent on the mating system and type of commercial production. In nature, pollination of papaya occurs through bees, butterflies, and wind.</p>

<p style="text-align: justify;">Papaya is usually described as sexually incompatible with other members of the Carica genus of which there are 23 described species. Initial steps have been taken to develop methods for somatic hybridization of <i>C. papaya</i> with <i>C. stipulata</i> and with <i>C. pubescens</i>, but no hybrid plants have been regenerated to date. The exact origin of papaya is unknown but thought to be native to tropical America, possibly southern Mexico or northwestern South America. Distribution now extends throughout tropical America, South-East Asia, India, Oceania, and Africa. Commercial production of papaya in the United States is primarily in Hawaii with secondary production in Puerto Rico and southern Florida.</p>

<p style="text-align: justify;">The food and livestock feed safety of papaya lines 55-1 and 63-1 was established based on several standard criteria. As part of the safety assessment, the nutritional composition of papaya fruit was found to be equivalent to conventional varieties by the analyses of vitamins A and C, and total soluble solids, which is a measure of sugar content. The latex of green papaya tissues contains a toxin called benzyl isothiocyanate (BITC) that has been linked to incidents of spontaneous abortions in pregnant women and with a higher incidence of prostate cancer in Japanese men over the age of 70. Because ripe papaya fruits have no latex they also have virtually no BITC content. The levels of BITC in transgenic papaya and conventional papaya varieties were measured and found to be much lower in ripe fruit compared to immature fruit. There were no differences between transgenic papaya and conventional papaya from either immature or ripe fruit.</p>

<p style="text-align: justify;">The PRSV coat protein does not possess characteristics typical of known protein allergens or toxins such as heat stability and resistance to digestion by simulated gastric fluids. Comparisons of the deduced amino acid sequence of the plant-expressed PRSV CP did not reveal any homology to known protein allergens and toxins. Furthermore, PRSV-infected papaya fruit naturally contains higher levels of the viral CP than expressed in these transgenic papayas, and there has been no evidence of adverse effects linked to the consumption of virus-infected fruit.</p>
