Cornell University and the University of Hawaii today unveiled two lines of papaya that could save the $45 million Hawaiian papaya industry. "SunUp" and "Rainbow" look and taste like their "Sunset" predecessor and are resistant to the papaya ringspot virus (PRSV), which is destroying the Hawaiian crop.
Papaya is the nation's first genetically engineered fruit crop to be cleared for eventual commercial production. The USDA removed regulatory restrictions on growing the two new cultivars earlier this month.
"Deregulation is the first big hurdle in commercialization," said plant pathologist Dennis Gonsalves of Cornell's New York State Agricultural Experiment Station in Geneva, N.Y., who has been involved in papaya research since 1978. "Commercialization could save the entire Hawaiian papaya industry. Our cultivars have shown excellent resistance in the laboratory, in the greenhouse and in long-term field trials."
Gonsalves has been cooperating closely on the papaya project with horticulturist Richard Manshardt of the University of Hawaii, Honolulu-based USDA plant physiologist Maureen Fitch and Upjohn Co. scientist Jerry Slightom.
Researchers developed the genetically engineered papaya lines by using recombinant DNA techniques to isolate and clone a PRSV gene that encodes for production of the viral coat protein. The gene was "shot" into cells of the papaya plant using a special gene gun developed at the Experiment Station. Expression of the gene in the resulting papaya line renders it resistant to the virus.
Papaya, one of the five largest crops in Hawaii, has been decimated in recent years by PRSV, which reduces fruit quality and eventually kills the trees. Many Hawaiian papaya growers believe that without PRSV-resistant papayas, the state's commercial papaya production virtually will be eliminated. PRSV infects papayas worldwide.
Jim Hunter, director of the Geneva Station, compares the process of conferring resistance to a kind of "molecular immunization." Researchers at Geneva selected papaya as a "model system" to develop the technology for genetically engineering virus resistance in fruit crops. Papaya, a fast-growing tree fruit, comes into production within nine to 12 months.
"Our intention is to engineer virus resistance into important New York fruit crops like apples and grapes," Hunter said. "It is fortunate that Dennis' experimental work with papaya has immediate application in the tropical regions of the world, where papaya is such an important crop."
Gonsalves, who was named to a Liberty Hyde Bailey Professorship at Cornell in November 1995, directs a research program at Geneva that uses both conventional techniques and the latest molecular technologies to breed disease resistance into fruits and vegetables. He collaborated with Asgrow Seed Co. on the development of Freedom II, a genetically engineered virus-resistant squash that was commercialized in 1995.
Genetic engineering of fruits and vegetables can increase quality and other desirable characteristics while decreasing the amount of chemicals required for pest control. Bioengineering desired traits also reduces the time it takes plant breeders to alter a plant by traditional breeding methods and can save millions of dollars in crop development.
"These papaya lines pose no plant pest risk and, therefore, should no longer be considered as regulated articles under our regulations governing the introduction of certain genetically engineered organisms," said John H. Payne, acting director of Biotechnology, Biologics and Environmental Protection with the USDA's Animal and Plant Health Inspection Service (APHIS).
The transgenic papaya will have no harmful effects to humans since PRSV-infected fruits, which contain the gene, are commonly eaten by consumers. Sugar levels are also the same, said Gonsalves, noting, "The only way we have affected papaya quality is to make it resistant to PSRV, which improves its survivability."
"Deregulation is a major positive step which augurs well for rapid adoption and acceptance of other agricultural biotech products," said Lynn W. Jelinski, director of the New York State Center for Advanced Technology in Biotechnology at Cornell, which provided partial funding for the project. "Dennis has a special gift for combining outstanding science with real-world problems to make a positive impact on society," Jelinski said.
USDA deregulation is a major milestone in the path to commercializing a PRSV-resistant papaya, but several hurdles remain. Other federal agencies, including the Food and Drug Administration and the Environmental Protection Agency, also must clear the genetically engineered papaya. In addition, licenses for use of the new technology for papaya production are still being negotiated with corporate patent holders. This aspect is being handled by the Papaya Administrative Committee, based in Hilo, Hawaii, which manages the federal marketing order for the fruit.
Production of sufficient "SunUp" and "Rainbow" seed to meet the papaya industry's needs also will require time, so the cultivars will not be immediately available. The first virus-resistant papayas could begin to appear in grocery stores in 1998.