The curious case of the genetically modified papaya.
By Jennifer Mo.
Stop by the farmers’ market in Hilo, Hawaii, and you’ll find knobby cherimoyas, avocadoes the size of eggplants, and mounds of papayas sunset-fleshed and as smooth and sweet as custard.
That wasn’t always the case. Back in the 90s, Hawaiian papaya farmers were faced with devastation from ringspot virus, a plant virus that reduced papaya production by 50 percent within six years and just kept spreading. Small farmers faced losing their livelihoods when one plant pathologist developed a virus-resistant variety called the Rainbow and distributed the seeds to struggling farmers—for free. Fourteen years later, Hawaii’s small papaya farmers are flourishing.
There’s a lot to like about this story—the altruism of the researcher, the success of independent local farmers. But there’s one detail that could change everything about how you see it: the Rainbow papaya is genetically modified.
A gene from the ringspot virus was inserted into the papaya, where it acts like a built-in vaccine against the virus. In other words, it’s Frankenfood. Or is it?
I say GMO, you think: Monsanto, Big Ag, lobbyists, corporate interests. But none of these played a major role in the GM Rainbow papaya. And for me, that led to an important realization. Genetic engineering technology is not the same thing as Monsanto/Big Ag policy. It’s a tool. And like all tools, it can be used for good or bad ends.
I’m a skeptic, so I scoured the web for info—agricultural news sites, activist sites, USDA releases, science journals and blogs. Then I took my questions to the man who developed the Rainbow, Dr. Dennis Gonsalves, retired Professor Emeritus of Plant Pathology at Cornell and now the director of the USDA’s Pacific Basin Agricultural Center.
He’s a straight shooter, detailing the successes and challenges of the project with peer reviewed articles and independently verifiable facts. Halfway through our exchange, it hits me:
Why shouldn’t we always address our science questions to scientists, not lobbyists or activists?
In that spirit, I’ve included his answers to my questions below.
Q: How did you get started with your work on the transgenic papaya?
I was born and raised on a sugar plantation on Hawaii Island but never aspired to be a scientist until I worked as a technician under Dr. Eduardo Trujillo of the University of Hawaii. He let me loose trying to figure out what was causing a disease of papaya and that experience convinced me that I wanted to be a plant pathologist. Dr. Trujillo was a mentor and an inspiration to me as he would periodically tell me: “Dennis, don’t just be a test tube scientist, but do things to help people.” […]
The feeling of joy was incredible when I first inoculated the transgenic papaya in the greenhouse and it showed resistance to PRSV [papaya ringspot virus]. However, that was nice science but how could we translate it to helping people? Naturally, the challenge came when PRSV invaded the Puna district and within a couple of years the Hawaiian papaya industry was in deep trouble. We had a potential solution, had published some nice papers, but did we have the guts to try to help the industry survive?
We had never attempted to deregulate a transgenic product, as the common thought was that this was the purview of the big companies. But somebody had to do it, and thus we got out of our comfort zone in order to help the farmers.
Q: Did you really give out GE (genetically engineered) papaya seeds for free to farmers?
The seeds were initially distributed free to the growers because I believe the industry (Papaya Administrative Committee) got some grant funds from the state to produce the seeds. Now, the industry produces the seeds and sells them at cost to the growers.
Q: What non-GE methods were used to attempt to combat ringspot virus on Hawaii?
People have been trying to do classical breeding to get resistance for a long time. In Carica papaya, there is no resistance. Some tolerance is found and people have been trying to incorporate these in some lines. The tolerance is “quantitative” so it can get diluted. Bottom line, this has not worked for Hawaiian papaya.
Crops rotation, lower densities, etc. have been tried but they do not work because the virus is rapidly transmitted by aphids. One way that can work economically is to go into virgin areas where it is far from the nearest virus infected papaya, and continually pull out trees as symptoms develop on the new planting. […] Naturally, the more isolated you are the longer for the virus to “find” the papaya field.
One question is: Environmentally, is it better to clear virgin forest or land to plant papaya than growing virus resistant GE papaya where papaya growing areas already exist?
Q: Could transgenic papayas eventually lose their immunity to ringspot virus? Is it true that GE papaya is more susceptible to fungal infections?
We always had the concern that our GE papaya would break down by new strains of the virus. Thus, we tested many isolates of the virus collected in Hawaii to see if strains that could break down the resistance were already in existence. Our results showed that our papaya were resistant to strains in Hawaii. However, we tested strains from outside of Hawaii and did find that our transgenic papaya were susceptible to a number of the strains outside of Hawaii, for example from Thailand, Taiwan, China, etc. […] As you probably know, we have not had breakdown of resistance in Hawaii since Rainbow was released in 1998.
Susceptibility to black spot fungus is not determined by its transgenic nature. If you crossed non-GE Sunset with non-GE Kapoho the susceptibility of the papaya to black spot would be the same as the Rainbow cross, which is GE Sunset crossed with non-GE Kapoho.
Q: Is it safe for humans to eat ringspot virus?
PRSV breaks down in three seconds in the human stomach. Ringspot virus has been around a long time and people have been eating virus infected produce for many, many years. As mentioned earlier, papaya infected with the mild strain PRSV were grown widely to combat the disease and infected fruit were eaten and commercially marketed, especially in Taiwan. […] In the mid 1990s when PRSV was devastating the industry in Hawaii, a great majority of the papaya were infected, and they were being consumed by people.
Q: Have there been any reports on allergies related to GE papayas since they were introduced in 1998?
We have done very thorough studies on allergenicity potential of GE papaya and found none. These studies are published in refereed journals. Don’t know of any verified reports.
Q: What is the rate of hybridization and what problems does hybridization between non-GE and GE varieties pose to human health and environment?
We recently completed a very thorough gene flow study under commercial conditions where the GE field was adjacent to non-GE field. In non-GE papaya fields separated from GE field by a 12 foot road, the rate of gene flow to the non-GE papaya row that bordered the road was about one percent. Further in the field we did not detect any gene flow. The bottom line is the pollen flow can occur, but it is very low.
In my opinion, we absolutely expected gene flow to occur, the very low rate likely due to the fact that commercial papaya in Hawaii is hermaphrodite (flower has male and female parts) such that the flowers are largely self-pollinated at the time it is opened.
Hybridization of the GE papaya to non-GE papaya will not pose any human health problems. We have thoroughly studied the potential health issues of the GE papaya and have found none.
Q: Monsanto has a patent on the transgenic technology you used to develop the Rainbow papaya. Does that mean that organic papaya farmers who experience hybridization can be sued by Monsanto?
Monsanto issued the license of these technologies to the Hawaiian papaya industry (Papaya Administrative Committee […] and later transferred to the HPIA (Hawaii papaya industry association). Thus, organic papaya farmers’ crops hybridizing with GE varieties will not result in lawsuit from Monsanto since they licensed the technology to the above organizations to commercialize the papaya in Hawaii.
Q: Japan approved GE papayas for import in late 2011. How do Japan’s safety standards for GE foods differ from the U.S.’s and what additional testing did the Rainbow undergo to receive approval?
The Japanese were very interested in allergenicity, and food safety, and knowing the host sequences bordering the “transgene inserts.” Additional field testing we did were to determine the nutritional content of the papaya at different stages after picking.
Q: What kind of long term impact do you think the GE papaya will have on humans and the environment?
The transgenic papaya has been grown commercially in Hawaii since 1998 and there has been no impact of human safety and the environment. In fact, in relation to the environment, it has had a positive impact because it allows the farmers to continually grow papaya in the historic areas where papaya was grown commercially and not force the farmers to go to virgin lands to escape the virus. […]
From the human health side, papaya is one of the most nutritious and economical fruit crops in the world. If PRSV had taken over in Hawaii, the fruit would have been largely unavailable, virus infected and very expensive. Now, you can go to farmers’ markets and buy four transgenic papaya for one dollar! Can you imagine that! That is a very cheap source of good tasting and nutritious fruit crop.
Q: What does the future hold for virus-resistant transgenics?
I am currently on a scientific advisory board of a Danforth Foundation grant from the Gates Foundation that is aimed at developing virus resistant cassava for Africa. The data looks extremely promising and no doubt the virus resistant transgenic cassava could help people in dire need. Soon we will face the moment of truth for such an important crop—will they be required to go through unnecessary tests and take unnecessary time and so forth just because of politics and philosophical views, even though the data shows that it is safe?
As I draw my career to a close and retire at the end of this year, the transgenic era has indeed been a wonder scientific research era, it has shown great promise especially for virus resistant crops, but so few products have been commercialized to help the people. It will be interesting to see what the next 25 years will bring.
This work has not made me rich but has brought great satisfaction in seeing that people have been helped. Some people are philosophically against GMOs, and that is okay. My aim was to do good science and make a scientific judgment on the safety of the transgenic papaya for humans and that it did not pose risks to the environment.
We have gotten much publicity on this work, but one of my most satisfying feelings came from the following incident. Several years ago, I was in the hospital [when] a Filipino hospital custodian came to me and said, “I know you, you are Dr. Gonsalves and I am so happy because I can still grow papaya because of papaya you developed.” The next day, he brought his family to see me in the hospital. This is what I call satisfaction in following Dr. Trujillo’s advice, “Dennis, don’t just be a test tube scientist, do something to help people.”
I think it’s fair to have some lingering questions about the GE papaya—questions about monocropping, labeling, long term effects.
After all, it’s impossible to anticipate the full impact of any of our actions, including a technology as complex and powerful as genetic engineering. I also think it’s fair to check up on the facts Dr. Gonsalves provides and to insist on published articles in peer-reviewed science journals. But after reading these articles and listening to arguments on both sides, I’m persuaded that the Rainbow was an appropriate and, yes, ethical use of genetic engineering that has had more benefits than drawbacks. This doesn’t mean I’m pro-GMO or pro-Monsanto. I’m pro asking questions and looking at situations on a case-by-case basis.
When I was in Hawaii recently, I did something that would have been unthinkable for me a few years ago. I bought papayas at the Hilo farmers’ market that I knew to be genetically engineered and ate them. They were delicious.
What questions do you have about the transgenic papaya? Would you eat one?
Jennifer Mo is a concerned global citizen and a long time cat/book/tree person. You can follow her green journey at It’s Not Easy to be Green.
This is a repost with permission of the author from Elephant Journal.