Papaya Ringspot Virus, and the “SunUp” and “Rainbow” Papayas
The genetically modified trees that saved a species
Whenever I see photos of the symptoms of Papaya Ringspot Virus (PRSV) up close, I actually think that if it weren’t so destructive, if would be beautiful.
One of the two strains of this Potyvirus, called PRSV-P, infects both Papayas (Carica papaya) and cucurbits (Cucurbitaceae); the plants suffer mosaic (interference with photosynthesis), leaf distortions, patches of necrotic tissue (which invites fungal infection), deformities in the fruit, and greatly-reduced yields. The virus is highly infectious, moving rapidly from plant-to-plant, primarily through aphid predation.
After being introduced to Hawaii in the 1930s, the virus mutated, and by the 1950s had halted 94% of Papaya plantations on Oahu. Production moved to other islands, but the pathogen followed, and also began infecting home gardens in the 1970s. Even with aggressive horticultural and insecticidal management, by the 1990s, the virus infected commercial plantations, and over 50%-80% of the industry was decimated in various global sites of production.
Carica papaya is a rather genetically homogenous tree, so there were few reservoirs of resistance to the virus to be found in feral or wild populations of the plant. As a result, something else needed to be done to save the production of this fruit: in 1998, the answer came in the form of genetic engineering.
The Transgenic Papaya
At Cornell University, Dennis Gonsalves from Kohala, Hawai’i, created the “SunUp” and “Rainbow” Papayas (the latter is an F1 hybrid of the former and the red-fleshed “Kapoho”). [x]
Using a tool called a gene gun, the embryogenic tissues of this plant were injected with a benign protein coat of PRSV-P (the virus that plagued them), which basically operates on the same principles as a vaccination: plants with this protein coat are immune to the virus, and also provide a sort of herd immunity to non-GM plants, by breaking up corridors of transmission (the virus is spread during pruning, or by sucking pests like aphids).
Today, over 80% of papayas sold globally are genetically modified to be immune to this virus. When these transgenic varieties were introduced, seeds were given away to farmers for free, and though there has been gene flow into conventional papaya populations (about 1%, as most commercial papayas are hermaphroditic and self-pollinating), there are no patent restrictions on private individuals re-planting seed from GM papayas.
Some times seeing all the feral cats on the island makes me sad and I just want to give them all homes and hugs, but other times I see a cat like this that looks well fed and healthy and I think, some of these cats actually have the greatest lives. They get to live in a jungle and be free to chase all the birds that they want and nap in any tree they desire and be little badass miniature leopards.