It started with rotting flesh and threatened to decimate an $11 Million industry in Hawaii. In 1949 the Papaya Ringspot Virus (PRSV) was discovered and named. PRSV is a part of a major Genus of plant destroying viruses called Potyvirus. This virus is economically important as it causes a major disease of the papaya. PRSV infects papayas systemically. Symptoms on papaya include leaves that develop a prominent mosaic and water soaked oily streaks on the petioles and upper part of the trunk. Severe symptoms often include a distortion of young leaves which also result in the development of a shoestring appearance that resembles mite damage. Trees that are infected at a young stage remain stunted and will not produce an economical crop. Fruit from infected trees may have bumps like that observed on fruit of plants with boron deficiency and often have ‘ringspots’, which is the basis for the disease’s common name. A severe PRSV isolate from Taiwan is also known to induce systemic necrosis and wilting along with mosaic and chlorosis.[1]
Research in both Hawaii and Taiwan began quickly to determine if the papaya had any natural resistance to the virus but there was none found. Next, a technique called Cross Protection was trialed on a small scale. Cross Protection is a vaccination technique where crops are inoculated with a mild strain of the virus for the plant to develop its own resistance; much like humans do when given vaccines against viruses such as measles. While this worked in small trials when the technique was pushed out to larger crop areas there were several issues; the largest issue was that the inoculation added no resistance against the most virulent and economically damaging strains of the virus. This practice was abandoned shorty after its inception in the 1980s. [2]
In 1992 a Hawaiian born scientist named Dennis Gonsalves began working on a solution utilizing biotechnology. Viruses work by infecting healthy cells and inserting a gene into either host DNA or RNA. As the DNA and RNA are directed to be transcribed the healthy cell is tricked into making more and more copies of the virus until the cell lyses and dies. PSRV is an RNA virus and in studying where this virus inserts its RNA into the healthy host cell the team of scientists was able to determine that they could remove or silence the transcription process at the exact spot the virus modified the RNA of the healthy host cell. No transcription means no virus reproduction which means the plant remains healthy. This technique is called post transcriptional gene silencing and has been so successful in saving the papaya, that it is being looked at in other plants that are susceptible to deadly viruses.[3]
Without biotechnology, “There’s no papaya industry. Simple as that,” said Dennis Gonsalves, the scientist who developed the Rainbow Papaya. Gonsalves and his team planted a trial of the Rainbow papaya on the Hawaiian island of Puna. Within 11 months, the non-GMO papaya became infected with the virus. After 27 months, The New York Times explains, “Standing dark green and papaya-laden, the trees provided 125,000 pounds of fruit per acre in a year; the conventional trees, stunted with yellowed, mosaic leaves, average 5,000 pounds.” The team of scientists then worked with a public-private partnership to help make the seeds commercially available to farmers. Within two years, more than half of all the papaya grown on Hawaii was GMO. A decade later, GM papaya accounted for over 90 percent of papaya production.[4]
For farmers, the GMO papaya has made a world of difference. “GM papayas mean sustainability for our family farm. The farm started with my grandfather and went to my dad, now my brother and hopefully another generation,” states Joni Kamiya, the daughter of a Hawaiian papaya farmer. The difference of going GM means one less worry about crop failure from a virus that remains ever-present to this day.
[1] “Papaya Ringspot Virus.” USDA/ARS Pacific Basin Agricultural Research Center, Hilo, HI. D. Gonzales, S. Tripathi, et. al. 2010
[2] “Engineered Mild Strains of Papaya ringspot virus for Broader Cross Protection in Cucurbits.” Phytopathology. B.J. You, et. al. 2005
[3] “Gene Technology for Papaya Ringspot Virus Disease Management.” The Scientific World Journal. Volume 2014, Article ID 768038. A.K. Azad. et. al. 2014
[4] “How GMO Technology Saved the Papaya.” International Food Information Council. 2016. https://foodinsight.org/how-gmo-technology-saved-the-papaya.