Many genome-editing applications are designed to help farmers increase the yield of their crops. But in some alarming cases, genome editing is the key to the species’ very survival. Take orange growers in Florida, the world’s second biggest producer behind only Brazil. They have seasonal challenges to overcome: arctic air plunges courtesy of the polar vortex, Atlantic hurricanes tearing up orchards, not to mention political headwinds impacting migrant workers. But the biggest threat is from an invisible source that was only first noticed in the Sunshine State in 2005.
The fruits that supply your freshly squeezed morning orange juice were first cultivated in China some 4,000 years ago, and imported to Europe about five hundred years ago. But a bacterial disease called huanglongbing (HLB), also known as yellow dragon disease or citrus greening disease,I has decimated the citrus industry in Florida and may do the same in California. It is caused by a bacterium called Candidatus Liberibacter asiaticus (CLas). The bacteria are spread by an insect, the Asian citrus psyllid, which feasts on phloem the way mosquitoes gorge on blood.
HLB causes the roots of infected trees to swell and then shrink, depriving the plant of water and nutrients. Meanwhile, the leaves producing sugars via photosynthesis can’t transfer them to the rest of the plant because the phloem is blocked. It’s like being starved and constipated at the same time.26 The affected oranges are green, misshapen, and sour, unsuitable for consumption or even concentrate. “It’s like AIDS but in citrus,” is a common saying in Florida farming circles.27
First detected in southern China about one hundred years ago, HLB probably arrived in the United States surreptitiously in the 1990s. Research is hampered by the difficulty in culturing CLas in the laboratory. The economic damage in China, South America, and now Florida is reaching pandemic proportions, with orange groves and fruit production dropping 20–30 percent in the past decade. Tens of millions of trees have been lost worldwide; tens of thousands of jobs and some $5 billion in Florida alone are at risk.
Traditional weapons are ineffective. The insect that carries HLB is hardy with a range that can evade pesticide sprays. Antibiotics are of limited value, as spraying is unable to reach the bacteria hovelling deep inside the orange trees. Many farmers resort to spraying a chemotherapy cocktail of herbicides, pesticides, and fertilizer to combat HLB and citrus canker.
Until recently, it didn’t appear that orange trees or any other cultivated citrus crops possessed any natural immunity. Hope grew a few years ago in the form of the Sugar Belle, a cross between a sweet clementine and the Minneola tangelo that is naturally resistant to CLas, growing more phloem to counteract the infection. Another idea is phage therapy, genetically arming a virus that, like CLas, naturally infects the phloem. And then there’s CRISPR:28 one idea is to pump up the promoter that governs activity of a family of plant protease genes to combat the bacteria. But there are challenges in editing polyploid plant species like citrus.29 The clock is ticking in Southern California as HLB threatens commercial groves.30
Southern Gardens Citrus, a subsidiary of U.S. Sugar, is spending millions of dollars on transgenic oranges in a bid to save the entire orange business facing collapse. “We are science geeks,” the firm declares proudly on its website. Obviously claims of “100 percent natural” won’t fly with the insertion of a transgene. “People are either going to drink transgenic orange juice or they’re going to drink apple juice,” is how one scientist puts it.31
One strategy is to create a “transgenic tree”—a more hostile environment for the bacteria or the insect. Botanist Erik Mirkov has considered scorpion venom, beetle toxin, even a pig gene. But you don’t need a PhD to realize that consumers would prefer not to have their orange juice spiked with sarcophagus beetle toxin DNA.32 The most palatable prospect is an antibacterial gene derived from spinach that encodes a defensin, a hole-puncher protein that punctures the CLas outer membrane. If Southern Gardens can navigate the approval processes, commercial transgenic trees could be planted soon.II
In 1923, Eddie Cantor had a No. 1 hit record with, “Yes! We Have No Bananas,” written by Frank Silver and Irving Cohn. Silver based the song on a lament he heard from a Greek vegetable stand proprietor on Long Island. Back then, the tasty variety of banana on sale was known as Gros Michel. But in the early 1900s, plantations in Central and South America were attacked by a fungus called Panama disease. By the 1950s, the Gros Michel had vanished from fruit stands. The fungus, which invades the plants via the roots, is almost impossible to eradicate from contaminated soil. In 2009, author Dan Koeppel, who literally wrote the book on bananas, was in the Democratic Republic of Congo, when he chanced upon someone ferrying bananas across a river. To his astonishment, he recognized them as the vanishingly rare Gros Michels. He peeled back the thick skin and savored his first bite as if sampling a vintage Château Margaux. His verdict was robust, creamy, with notes of… “It tastes more like a banana,” he said approvingly.33
The banana industry was saved from collapse by the Cavendish variety, derived from plants grown in the 1830s at Chatsworth House, an English stately home. The Cavendish is an inferior fruit in most respects but became a commercial mainstay thanks to its resistance to the Panamanian fungus. Or at least it was before “bananageddon.” We can’t say we weren’t warned.
The Cavendish is a monoculture, incapable of evolving because every fruit is a genetic clone. The Panamanian fungus, however, is under no such constraint, and a new strain called Fusarium TR4 (or Tropical Race Four) identified the Cavendish’s Achilles’ heel. TR4 arose in Taiwan in the 1980s, spread to Australia, and in 2014 jumped to Africa and the Middle East. Five years later, in August 2019, the Colombian Ministry of Agriculture declared a national emergency as TR4 struck in South America, the source of three quarters of the world’s banana exports.34
There are more than a thousand varieties of banana, but whether consumers, who eat one hundred billion bananas a year, will accept a substitute that doesn’t look like a traditional banana is a big question. Maybe they would prefer a fruit that has been genetically modified? A British company, Tropic Biosciences, is using CRISPR to reprogram some of the plant’s own RNA interference defenses to target the fungus.35 The company is also engineering coffee plants that will be genetically depleted of caffeine.
The threats to oranges and bananas illustrate the dilemma that all farmers and agricultural biotech business are now confronting: how to reassure the public that genetically modified, potentially gene-edited, fruits and crops are safe in an age of misinformation, fake news, and a legacy of anti-GMO disinformation. Some manufacturers have brazenly capitalized on this fear and ignorance by slapping “non-GMO” labels on all sorts of foods and fruits—even those that by definition cannot be genetically modified. Take water—an oxygen atom sandwiched between two hydrogen atoms—or salt, the simple union of sodium and chloride ions. These are two of the most natural, ancient compounds on earth. They couldn’t be genetically modified if you tried.
Klaas Martens, an organic farming luminary in New York State, is a long-standing opponent of GMOs and the uses of genetic engineering technology such as Roundup for a manageable problem. “When the only tool you have is a hammer, everything turns into a nail,” Martens says. But he sees CRISPR as a promising tool that could in some instances be compatible with organic agriculture if it could enhance the natural system.36