by Bryce Axelrod, Sustainable Plant Systems major
The papaya ringspot virus (PRSV) or Potyvirus is a major disease of papaya (and cucurbits) and is a virus that is found in all the areas of the world where these crops are cultivated.
The virus typically infects the papaya in the Caricaceae family and members of the Cucurbitaceae family while also having alternate hosts in the Chenopodiaceae family, specifically Chenopodium amaranticolor and C. quinoa. With there being multiple hosts, there are multiple opportunities for infection, especially if crops are placed nearby one another.
The disease is transmitted by means of aphids and is typically non-persistent in the vectors themselves, meaning that the virus does not replicate and eventually becomes unapparent. The disease/virus will, however, persist for a short amount of time in the vector and the spreading occurs in rapid movement and feeding of the vector from an infected plant to an uninfected plant.
Papayas originally were mostly grown in Oahu, Hawaii but in the 1950’s, the virus hit those crops and relocation to Puna was necessary. The virus was found again in Hilo in the 1970’s and investigations to develop the GE papaya started in 1985.
Hawaii’s largest yield of papaya was 80.5 million pounds in 1984. At the time, Hawaiians probably figured that this would be their all-time high due to the virus being found in nearby regions and did not want to see a decline, but efforts were not quick enough.
By 1991, scientists had figured it out and developed a transgenic papaya that was resistant to the virus. This new variety contained a gene from the Papaya Ringspot Virus involved in the coat protein, protecting these papayas against damage from PRSV.
When the virus hit Puna in 1992, production levels were at 53 million pounds, about 65% of what it was just 8 years in the past. However, the commercialization of these new GE papayas had not occurred until 1998 and by this time, production levels were at 26 million pounds; essentially cut in half.
Japan was and is a major consumer of the Hawaii papaya and with the market in Japan being solely comprised of non-GMO products, they did not accept the new variety until December 2011.
This process with Japan and getting them to adopt the new variety indirectly plays a role in how other countries will accept GMO or transgenic products in the future and directly hindered the growth of the papaya market. Even with all of this said, the papaya yield in 2010 was at 30.1 million pounds; 4 million pounds more than the yield 12 years before in 1998.
At this rate of repair (4m lbs/12 yrs), it would take about 144 years to get the papaya industry back to 80 million pounds, where it was in 1984.
Assuming that the growth would begin to increase exponentially due to increasing farmland used and management methods progressing alongside, the process will go by much faster than previously calculated.
What is important is that the yields are increasing and reassuring that the industry and all of its members will continue.
Before transferring to Ohio State, my focus in horticulture was in Landscape Design & Management. While I enjoy the designing aspect of landscaping very much and would like to keep expanding in that area, I also really enjoy the care & management aspect of it as well which is why I changed my specialization from Landscape Design to Horticulture. At the same time, I also have an ever-increasing interest in greenhouse operations and the versatility of it all particularly with a few different areas of plant propagation (and its different methods) and also biological controls.
This blog post was an assignment for Societal Issues: Pesticides, Alternatives and the Environment (PLNTPTH 4597). The views expressed are those of the author and do not necessarily reflect the views of the class, Department of Plant Pathology or the instructor.