July 7, 2015 | By

Hawaiian Papayas and Florida Oranges: Combating Disease with Genetic Engineering

A worker reaches for a papaya in Waialua, on the North Shore of Oahu, in Hawaii. REUTERS/Yuriko Nakao

Science & Our Food Commentary Series

By Marcus Glassman, Research Associate, Global Agriculture & Food, The Chicago Council on Global Affairs

In the United States, many consumers view genetically engineered (GE) crops with fear, misunderstanding, and mistrust. The development of GE crops by largescale agriculture, and the business practices of largescale agribusiness, are often seen as one-in-the same.  Consumers view agribusiness and the GE seeds they produce as responsible for increased pesticide use, loss of transparency in our food supply, increased monoculture farming, environmental degradation; the list goes on and on. 

These objections tend to dominate the collective conversation around the current and future use of GE crops in American agriculture and our food supply. But these easy-to-see examples of GE—the ubiquitous corn and soybean fields across much of the US—are not the whole story. GE technology has been used for far more consumer-serving means than commodity crops; take, for example, the case of the Hawaiian papaya.

In the 1950s, Papaya ringspot virus (PRV) was first identified in papaya orchards on the Hawaiian island of Oahu. PRV causes infected papaya trees to produce disfigured fruit, unsuitable for market. Once a tree is infected, there is no cure. The arrival of the virus forced 95 percent of Hawaiian papaya production onto the then PRV-free big island of Hawaii; within 20 years, however, the virus was there, too. In 1978, concerned that the virus would devastate Hawaii’s papaya industry, Cornell University researcher Dennis Gonsalves began USDA-funded work to develop a PRV-resistant papaya. Using genetic engineering, his team spliced DNA from the PRV into the genome of a papaya, creating GE papaya trees that were immune to the virus. Those GE plants were used to create PRV-resistant crosses, and in 1998 those seeds were widely distributed for free to local growers in Hawaii; by September 1999, 90 percent of Hawaiian farmers had obtained GE seed.  In virus-infected areas—which included all of Hawaii by 1995—the GE papaya produced 20 times more fruit than infected trees, and the introduction of the GE papaya is credited with saving the Hawaiian papaya industry: Between 1998 and 2001, the total annual production of papaya in Hawaii had rebounded from a low of 26 million pounds, to a high of 40 million pounds.  

This use of public interest, not for profit genetic engineering is far removed from the typical connotations Americans have when they think of GE crops. The model created in Hawaii is a powerful one: Not just because it saved a crop and did so as a public good, but because the Hawaiian papaya is far from the last crop to benefit from genetic engineering to fight off disease. Florida’s oranges, for example, are fighting their own invasive disease that threatens the industry, and without GE intervention—and soon—Florida oranges could very likely be extinct.

In 2005, citrus greening was spotted in Florida.  The disease is caused by Candidatus liberibacter, a bacteria carried between orange groves by an invasive aphid-like insect called the Asian citrus psyllid. When infected, a tree produces shriveled, green oranges, and eventually dies. The disease has damaged citrus crops worldwide, and since its emergence in the US, has spread across US citrus-growing regions: To date, the entire states of Florida and Georgia are under quarantine due to the disease, as are portions of California, Louisiana, South Carolina, Texas, Puerto Rico, and the US Virgin Islands.

Since the arrival of citrus greening, Florida’s orange groves have shrunk 39 percent from their pre-citrus greening peak acreage; 80 percent of the state’s remaining 515,000 acres of orange groves are estimated to be infected by or at risk of citrus greening; and Florida’s orange crop is the smallest since 1966, with a predicted 2015 harvest down 60 percent from 2003. Recognizing the imminent danger to the Florida orange industry, Congress appropriated $125 million towards research in the 2014 Farm Bill.

Inspired by the success of the Hawaiian papaya, researcher Erik Mirkov at Texas A&M and Rick Kress, President, Southern Garden Citrus, have partnered on a solution.  With funds from Southern Garden Citrus and those appropriated to USDA/Texas A&M, Mirkov and his team have inserted genes from a spinach plant into the genome of an orange tree, creating a GE orange tree that, so far, shows promising signs of resistance to citrus greening.

There are other, non-GE solutions in the works, too: In Florida, researchers have tried putting trees in plastic tents; in California, researchers have released parasitic wasps from Pakistan that prey on the Asian citrus psyllid; and chemical treatments that may protect trees from the disease will be on the market soon.  However, none seem to have the potential impact to break the disease’s hold on the Florida orange as Mirkov’s experimental GE orange groves, which are already beyond their first stage of field trials.

But getting citrus greening-resistant orange trees into orange groves won’t be easy: There is still a long regulatory road to go.  It is Southern Gardens’ intention to deregulate its GE orange trees for free use, a usually prohibitively expensive process that requires sign-offs from the EPA, USDA, and FDA.

The final hurdle, though?—consumers. What will consumers think of GE orange juice? GE oranges? If consumers decide to buy imported non-GE oranges and orange juice in lieu of GE Florida oranges, the entire project will be sunk. Without market demand, the industry cannot stay afloat.

This is why it is so important to understand that genetic engineering is only a tool for precise plant breeding. Traditional breeding could have never delivered the spinach gene that renders orange trees immune to citrus greening in the way genetic engineering did; nor could traditional breeding have produced a papaya born with innate immunity to the ringspot virus as efficiently as genetic engineering. Just because this technology is utilized in unsavory ways by large agribusiness to advance farming practices not everyone agrees with, doesn’t mean the technology itself lacks value. If consumers come to understand the reality of what genetic engineering is, and what it can produce, we will be even more prepared to protect our favorite fruits the next time a seemingly unstoppable disease appears. 

Read additional posts in the Science & Our Food series:


The Global Food and Agriculture Program aims to inform the development of US policy on global agricultural development and food security by raising awareness and providing resources, information, and policy analysis to the US Administration, Congress, and interested experts and organizations.

The Global Food and Agriculture Program is housed within the Chicago Council on Global Affairs, an independent, nonpartisan organization that provides insight – and influences the public discourse – on critical global issues. The Council on Global Affairs convenes leading global voices and conducts independent research to bring clarity and offer solutions to challenges and opportunities across the globe. The Council is committed to engaging the public and raising global awareness of issues that transcend borders and transform how people, business, and governments engage the world.

Support for the Global Food and Agriculture Program is generously provided by the Bill & Melinda Gates Foundation.


1,000 Days Blog, 1,000 Days

Africa Can End Poverty, World Bank

Agrilinks Blog

Bread Blog, Bread for the World

Can We Feed the World Blog, Agriculture for Impact

Concern Blogs, Concern Worldwide

Institute Insights, Bread for the World Institute

End Poverty in South Asia, World Bank

Global Development Blog, Center for Global Development

The Global Food Banking Network

Harvest 2050, Global Harvest Initiative

The Hunger and Undernutrition Blog, Humanitas Global Development

International Food Policy Research Institute News, IFPRI

International Maize and Wheat Improvement Center Blog, CIMMYT

ONE Blog, ONE Campaign

One Acre Fund Blog, One Acre Fund

Overseas Development Institute Blog, Overseas Development Institute

Oxfam America Blog, Oxfam America

Preventing Postharvest Loss, ADM Institute

Sense & Sustainability Blog, Sense & Sustainability

WFP USA Blog, World Food Program USA