This publication is designed to accompany the video that must be viewed as part of the licensing process for anyone wishing to purchase seed of transgenic papaya cultivars. It describes the transformed University of Hawai‘i cultivars, their cultivation and marketing concerns, and addresses questions about food safety

Cavaletto, Catherine G.

DFerreira, Stephen J.

Llantero, Emerson

Manshardt, Richard M.

Mochida, Loren

Nishina, Melvin S.

Perry, Delan

ScholarSpace at University of Hawai'i at Manoa

Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June30, 1914, in cooperation with the U.S. Department of Agriculture. Charles W. Laughlin, Director and Dean, Cooperative Extension Service, CTAHR, Universityof Hawaii at Manoa, Honolulu, Hawaii 96822. An Equal Opportunity / Affirmative Action Institution providing programs and services to the people of Hawaii withoutregard to race, sex, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or veteran status.Cooperative Extension Service New Plants for HawaiiApril 1998NPH-2Papaya ringspot virus (PRV) has had a very signifi-cant impact on papaya production in Hawaii. Oahuwas the major production site in the 1950s, but the spreadof PRV caused the papaya industry to move to the Punaarea of the island of Hawaii in the 1960s. Since 1992,the introduction and subsequent spread of PRV in com-mercial orchards in Puna has resulted in a significantdecrease in the state’s papaya production.“Transforming” the papaya for virus resistanceFortunately for Hawaii’s papaya industry, help was onthe way. In 1987, researchers at the University of Ha-waii (UH) and Cornell University in New York had be-gun trying to create a “transgenic” papaya with virusresistance. They used “genetic engineering” or “genetictransformation” techniques to insert part of the virus intothe nucleus of a papaya cell. At Cornell, Dr. DennisGonsalves isolated the virus’ coat protein, and he andDr. Jerry Slightom of The Upjohn Company modified itfor use in plants. In 1989, quantities of the gene were“shot” into cultured papaya tissue using a “gene gun”developed by Dr. John Sanford at Cornell. Dr. MaureenFitch, then a graduate student at UH, developed a tis-sue-culture system needed to grow out the geneticallyengineered plants from the bombarded plant materials.In 1991, Gonsalves observed the first transformed plantthat appeared to have PRV resistance.At UH, Dr. Richard Manshardt used traditional plantbreeding techniques and inbred the resistant plant, pro-ducing a true-breeding, red-fleshed cultivar that wasnamed ‘UH SunUp’ (also referred to as ‘SunUp’). Be-cause the papaya industry wanted a yellow-fleshed fruit,Manshardt crossed ‘SunUp’ with ‘Kapoho’ to producea yellow-fleshed F1 hybrid that was named ‘UH Rain-bow’ (also called ‘Rainbow’).Production Requirements of the Transgenic Papayas‘UH Rainbow’ and ‘UH SunUp’Commercializing the transformed papayaHawaii’s Papaya Administrative Committee (PAC) as-sumed the task of obtaining license agreements withowners of the patented genetic engineering technology,while Gonsalves and Manshardt prepared and submit-ted technical documents required by the U.S. Depart-ment of Agriculture (USDA), the Environmental Pro-tection Agency (EPA), and the Food and Drug Admin-istration  (FDA). In September 1997 the federal regula-tory agencies completed their review and approved thetransgenic papaya for production and sale. PAC success-fully negotiated use licenses with Monsanto Company,Asgrow Seed Company, Cambia Biosystems L.L.C., andthe Massachusetts Institute of Technology.LicensesThe licenses negotiated with the four companies includelimitations-of-use and compliance provisions. There arefive provisions, common to all of the licenses, whichgrowers must follow to be in compliance with the con-tracts, as follows:• Transgenic papaya can only be planted in the state ofHawaii.• Only PAC can sell seeds of ‘Rainbow’ and ‘SunUp’.• Fruits can only be sold in countries that have acceptedgenetically engineered papayas as safe for commer-cialization.• Producers must attend an educational session, whichcovers the requirements of the licenses and PRV re-sistance management.• Producers are required to sign an agreement with thePAC to purchase seed.NPH-2 Production Requirements of ‘UH Rainbow’ and ‘UH SunUp’ CTAHR — April 19982Characteristics of papaya hybridsHybrids such as ‘UH Rainbow’ have some characteris-tics that are very different from the inbred papaya linessuch as ‘Kapoho’ that Hawaii growers are used to. It isimportant that growers understand these differences.The first difference is that the sex-segregation ratioof hybrids is 1:1 (one hermaphrodite to one female plant)rather than the more favorable 2:1 ratio with inbred lines.Consequently, growers will have to leave five seedlingsat each hole (rather than three) to ensure a 97 percentchance of having one hermaphrodite per hole at thin-ning time at flowering.The second difference is that plants grown fromseeds of F1 hybrids do not breed true, and growers mustpurchase new F1 seeds for each planting. If growers useseeds taken from the hybrid fruits they have grown, theresulting plants will have mixed characteristics. Someof them will be yellow-fleshed and some will be red-fleshed. More important, some of the plants will be re-sistant to PRV, while others will be susceptible to thevirus.Resistance managementWhenever new resistant varieties are planted widely,disease-causing organisms may change, acquiring theability to overcome or “break down” the resistance. Inpapaya, this could occur in two ways:• A new PRV strain could be brought into Hawaii; both‘Rainbow’ and ‘SunUp’ are highly resistant to thePRV strains found in Hawaii, but they are highly sus-ceptible to strains from Asia.• New PRV stains could develop from strains nowpresent in Hawaii; this could occur if virus-infectedplants are allowed to grow in or near fields of ‘Rain-bow’.‘SunUp’ is totally resistant to the virus, but ‘Rain-bow’, in greenhouse studies, has shown susceptibilityto PRV until about seven weeks of age. This is referredto as “young plant susceptibility.” The plants becomefully resistant to PRV after three months of age. Theseobservations suggest that in areas of high virus pres-sure, such as Puna, growers are likely to find infectedseedlings. It has also been observed that side-shoots onthe main trunk may show infection. If PRV symptomsare observed in a seedling field, all infected plants un-der three months of age should be removed from thefield immediately. If PRV symptoms are observed inplants older than three months, the symptomatic plantsshould be removed from the field and samples should betaken to the local Cooperative Extension Service officefor testing to determine if a new strain has developed.It is important that virus pressure on the new ‘Rain-bow’ and ‘SunUp’ cultivars be kept at a minimum tomaintain their resistance to PRV. This means that grow-ers must cut down all infected plants in and around fieldsof transgenic papaya plants. In addition, all abandonedpapaya orchards must be rogued completely of papayaplants to reduce virus pressure.Review of virus symptomsFrequent surveys of young plantings will ensure thatinfected trees are identified at the early-infection stage.• Leaves become yellowed and show a “mosaic” pat-tern of yellow to yellow-green discoloration.• Leaf shape can become distorted with an upwardcupping, and “shoe-string” symptoms (thinning ofthe leaf between the lobes) can be seen as the distor-tion becomes severe.• The leaves may also show “green islands” (patchesof green tissue).• Water-soaked streaks may be present on the leaf peti-oles.• Ringspot on the fruit is usually evident only after theinfection has been present for an extended period.Culture of ‘UH Rainbow’The culture and production of ‘Rainbow’ will be a littledifferent than growers are used to with the cultivar‘Kapoho’. ‘Rainbow’ seem to be sensitive to calciumdeficiency and requires application of 1500 pounds ofcalcium carbonate and 500 pounds of dolomite per acre.Since ‘Rainbow’ has ‘Sunset’ parentage, it requires ap-plications of 400 pounds of a fertilizer  such as 14-14-14 at intervals of four to five weeks.‘Rainbow’ seems to be a little more sensitive tophythophthora than ‘Kapoho’ and will require timelyapplication of fungicides. ‘Rainbow’ fruits seem to bemore tolerant of anthracnose than ‘Kapoho’ fruits. Thetransgenic cultivars have the same susceptibility to mitesand leafhoppers as ‘Kapoho’. The fruits seem to ripenfaster than ‘Kapoho’ but slower than ‘Sunrise’ fruits.NPH-2 Production Requirements of ‘UH Rainbow’ and ‘UH SunUp’ CTAHR — April 19983Marketing concernsGrowers must ensure that transgenic and non-transgenicpapaya fruits are kept segregated at harvest so thattransgenic fruits are sent only to accepting markets. Thenecessary practice of segregating transgenic varieties byblocks at planting should help to support this control.It is imperative that growers do not plant seed fromtheir own fruits of the F1 hybrid ‘Rainbow’ plants. Ifthis is done, the field will include a mixture of plantsbearing yellow-fleshed or red-fleshed fruits. This wouldcreate a serious problem for the farmer and marketersbecause there is no way to determine if the fruit fleshcolor is red or yellow without cutting each fruit. Also,some of the plants in the field will not be PRV-resistant,which can contribute to breakdown of resistance in thetransgenic plants. The related marketing concern is thattransgenic fruits from a mixed field may be moved bymistake into markets that do not permit them.Fruit qualityThe fruits of both ‘Rainbow’ and ‘SunUp’ are larger than‘Kapoho’ by about 50 percent. ‘Rainbow’ has a yellow-fleshed fruit which is slightly sweeter and juicer than‘Kapoho’ but has a slightly less intense aroma. ‘SunUp’has a pink-fleshed fruit and has fruit characteristics simi-lar to ‘Sunset’. ‘Rainbow’ has shown good tolerance tothe heat treatment that is required for fruit fly disinfes-tation.Food safety concernsWhat is genetic engineering?Genetic engineering is a molecular technology that al-lows the transfer of a genetic trait, such as virus diseaseresistance, from one kind of organism to another. In thecase of the genetically engineered papayas, a gene thatprevents infection by papaya ringspot virus was foundin the virus itself. It was transferred to a papaya, creat-ing a PRV-resistant variety.Why haven’t I seen other genetically engineeredfruits and vegetables in the market?Genetic engineering is a new technology, and ‘SunUp’and ‘Rainbow’ papayas are the first genetically engi-neered fruits to be commercialized in the United States.Is genetic engineering necessary?In some cases, yes. Some problems, such as overcomingPRV, cannot be solved without it. In papayas, there areno naturally occurring genes for effective resistance toPRV, so plant breeders have nothing to work with to im-prove the crop. Without the genetically engineered formof PRV resistance, the papaya industry in Hawaii wouldbe destroyed by the virus, resulting in lost livelihoodsfor growers and much higher prices for consumers.Is genetic engineering risky?Genetic engineering is a powerful tool for manipulationof biological organisms, and as such it has great poten-tial for beneficial use. However, as in any situation, hu-man fallibility raises concerns about the proper applica-tion of the new technology. We need to be assured thatgenetically engineered products serve the public good,not just the agenda of the producer. There is a societalneed for strict monitoring of the objectives and meth-ods of genetic engineering.How can I be assured that genetically engineeredfoods are safe?Development of genetically engineered crops and foodsis monitored by three federal regulatory agencies: theU.S. Department of Agriculture, the Environmental Pro-tection Agency, and the Food and Drug Administration.These agencies have examined the development of the‘SunUp’ and ‘Rainbow’ papaya cultivars and approvedthem as safe.Can I be infected with the PRV virus by eating ge-netically engineered papayas?Definitely not! Plant viruses like PRV cannot infect hu-mans. Furthermore, ‘Rainbow’ and ‘SunUp’ fruits con-tain only a tiny part of the virus’s genetic information,not the complete virus. There is no danger in eating ge-netically engineered fruits.Does genetic engineering make ‘UH SunUp’ and ‘UHRainbow’ better than other papayas?Yes! ‘SunUp’ and ‘Rainbow’ are high-quality solo-typepapayas, very similar (respectively) to ‘Sunrise’ and‘Kapoho’, which are popular standard varieties devel-oped in Hawaii and grown around the world. FollowingNPH-2 Production Requirements of ‘UH Rainbow’ and ‘UH SunUp’ CTAHR — April 19984the recent devastation of much of Hawaii’s papaya acre-age by papaya ringspot virus, genetic engineering hasprovided the two new transformed papaya varieties thatare resistant to the virus. This has enabled local growersto continue producing delicious, nutritious papayas andoffering them to consumers at affordable prices.SummaryThis publication is designed to accompany the video thatmust be viewed as part of the licensing process for any-one wishing to purchase seed of transgenic papaya cul-tivars. In addition, a sublicense agreement with the Pa-paya Administrative Committee must be signed beforeseed can be purchased. The video covers PRV resistancemanagement and the requirements of the sublicenseagreement.It is very important that everyone—both commer-cial producers and home gardeners—growing ‘Rainbow’and ‘SunUp’ adhere to the conditions in the sublicensethat they sign with PAC. The new transgenic cultivarswill allow papaya production in PRV-affected areaswhere it formerly was not possible. People growing themshould know the symptoms of PRV and the basic prin-ciples of PRV management. By carefully observing theirplants and following the conditions of the sublicenseagreement, papaya growers can help to ensure that thevirus resistance of ‘Rainbow’ and ‘SunUp’ is not com-promised and lost.For answers to questions about the sublicense, callthe Papaya Administrative Committee at (808) 969-1160.For questions regarding papaya cultivation or PRV re-sistance management, call your local Cooperative Ex-tension Service office.Melvin S. Nishina1, Stephen J. Ferreira2, Richard M.Manshardt3, Catherine G. Cavaletto3, Emerson Llantero4,Loren Mochida4, and Delan Perry41Cooperative Extension Service–Hilo, 2CTAHR Departmentof Plant Pathology, 3CTAHR Department of Horticulture,4Papaya Administrative Committee

Production Requirements of the Transgenic Papayas 'UH Rainbow' and 'UH SunUp'

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Production Requirements of the Transgenic Papayas 'UH Rainbow' and 'UH SunUp'

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