Economically hard hit in recent years by the papaya ringspot virus, papaya growers in Hawaii are depending on two new Cornell-developed, virus-resistant varieties -- called UH SunUP and UH Rainbow -- to restore the industry's sagging agricultural vitality.
Seeds from the genetically engineered fruit were distributed May 1, marking the culmination of over 20 years of work.
"This is the first case for commercialization of a genetically engineered, virus-resistant, perennial fruit crop," said Dennis Gonsalves, Cornell's Liberty Hyde Bailey Professor in plant pathology at the university's New York State Agricultural Experiment Station in Geneva. "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."
Papaya farming generates $45 million in annual revenues, making it Hawaii's fifth-largest crop; but yields have been dropping steadily. The virus reduces fruit quality and quantity and eventually kills the trees. From 1993 to 1997, papaya production fell from 58 million pounds to 36 million pounds.
"These seeds give the papaya industry in Hawaii a second chance," said Emerson F. Llantero, manager of the Papaya Administrative Committee (PAC), Hilo, Hawaii. PAC helped finance the costs associated with licensing the genetic engineering technology and producing seed.
"This genetically engineered, disease-resistant papaya is an excellent example of improving agricultural productivity through partnership," said Michael V. Dunn, assistant secretary for the United States Department of Agriculture's marketing and regulatory programs. "In this case, the partnership between USDA, Cornell and the University of Hawaii has resulted in a papaya that is environmentally safe, will lower input costs for producers, provide a better product for consumers and improve export potential."
In addition to Gonsalves, the research team that developed the improved papaya lines includes horticulturist Richard Manshardt of the University of Hawaii, Honolulu-based USDA plant physiologist Maureen Fitch, Upjohn Co. scientist Jerry Slightom and members of PAC.
The team used recombinant DNA techniques to isolate and clone a gene in the virus that encodes for production of the coat protein of the virus. The gene was "shot" into cells of the papaya plant using a special gene gun developed by John Sanford, Cornell associate professor of horticultural sciences at the Geneva Experiment Station. Expression of the gene in the resulting papaya line renders the plants resistant to the virus, thus producing more fruit of higher quality. Scientists have dramatic photographs of test plots where genetically engineered papaya trees are thriving next to virus-riddled, non-genetically engineered trees.
The transgenic papaya will have no harmful effects on humans because the virus already infects fruit that consumers eat. "The only way we have affected papaya quality is to make it resistant to the virus and improve its survivability," Gonsalves said.
The first fruit from the genetically engineered seeds should be available in stores in about a year.
James Hunter, director of the Geneva Experiment Station, compares the process of conferring resistance using a gene from the virus to molecular vaccination. "The techniques used to develop the resistant papaya are a 'model system' to investigate the practicality of cross protection to control other plant viruses," he said.
"Using a mild strain of a virus to protect plants against infection by a severe strain of the same virus is a potentially practical way to control virus diseases of crops important in New York -- especially the tomato ringspot virus infecting peaches and viruses infecting cucurbits," Gonsalves said. He envisions a worldwide network of scientists transferring knowledge and technology as well as cooperating in the sharing of genes to solve food problems in a global village of hungry people.
Genetic engineering of fruits and vegetables can increase yields while decreasing the amount of chemical pesticides required to grow them. Bioengineering desired traits can often reduce the time it takes plant breeders to alter a plant by traditional methods, perhaps by a factor of about five, saving millions in crop development.
The virus-resistant papaya were deregulated by the USDA's Animal and Plant Health Inspection Service, the Environmental Protection Agency and the Food and Drug Administration in 1997. In April of this year, the joint owners, Cornell and the University of Hawaii, licensed the PAC to grow, propagate and sell those papaya in the United States.
In anticipation of commercialization, PAC funded seed production over a year ago, and enough transgenic seed will become available during 1998 to replace all acreage damaged by virus in Hawaii. Seed is being produced by the Hawaii Agriculture Research Center under contract from PAC on about five acres of University of Hawaii land. It will furnish 27 million seeds within a three-year period.
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