42 Papaya
consumers, is even more crucial in developing countries where papaya is already
popular. GE papaya does not require changes in management practices or large capi-
tal investments, it does not alter production costs, and access to intellectual property
is already being negotiated in several countries in a philanthropic manner (Gonsalves
et al. 2007). Because the effects of PRSV have been as devastating in other countries
as they were in Hawaii, there is a clear need for a solution, and a demand by increas-
ingly vocal growers.
Papaya plants suffer from a plethora of viral diseases. Papaya ring spot virus
(PRSV) is more devastating and can be transmitted by infected seeds used for propa-
gating the genotype (Verma 1996). Since there are fewer virus particles in apical
meristems, the tissue culture technique of meristem culture has been developed as an
important and effective method for elimination of viruses. However, all regenerated
plants must be checked for presence of virus particles by standard ELISA technique
or by cDNA probing. Disease free meristem is, thus, an ideal source material for
micropropagation.
In the late 1980s, the University of Hawaii began developing a papaya resistant to
papaya ring spot virus. To do this, certain viral genes encoding capsid proteins were
transferred to the papaya genome. These viral capsid proteins elicit something simi-
lar to an ‘immune response’ from the papaya plant. These new, genetically modified
papaya plants are no longer susceptible to infection, allowing farmers to cultivate
the fruit even when the virus is widespread. The first virus-resistant papayas were
commercially grown in Hawaii in 1999. Transgenic papayas now cover about one
thousand hectares, or three quarters of the total Hawaiian papaya crop. Genetically
modified papayas are approved for consumption both in the US and in Canada.
Several Asian countries are currently developing transgenic papaya varieties resis-
tant to local viral strains (Ray 2002).
Since the PRSV is a major problem in many papaya growing areas, develop-
ment of genetically resistant cultivars has been greatly envisaged. Papaya ring spot
virus (PRSV) is often a limiting factor in the production of papaya worldwide. In
1992, PRSV was discovered in the district of Puna on Hawaii Island, where 95% of
Hawaii’s papaya was grown. Within two years, PRSV was widespread and causing
severe damage to papaya in that area. Coincidentally, a field trial to test a PRSV-
resistant transgenic papaya had started in 1992, and by 1995 the ‘Rainbow’ and
‘SunUp’ transgenic cultivars had been developed. These cultivars were commer-
cialised in 1998. ‘Rainbow’ is now widely planted and has helped to save the papaya
industry from devastation by PRSV. Transgenic papaya has also been developed for
other countries, such as Thailand, Jamaica, Brazil and Venezuela. Efforts to have
these papaya deregulated in these countries are ongoing. Farmers quickly planted
the transgenic papaya seeds, which were nearly all ‘Rainbow’ because the farmers
in Pune favoured this transgenic cultivar (Gonsalves 1998). Harvesting of ‘Rainbow’
started in 1999 and grower, packer and consumer acceptance were widespread. The
papaya industry had been spared from disaster. Since 1992, when the virus was dis-
covered in Pune, the yearly amount of fresh papaya sold from Pune had gone from
53 million pounds in 1992 to 26 million pounds in 1998. In 2001, Pune papaya pro-
duction rebounded to 46 million pounds of fresh market papaya. Another important
impact has been the dramatic reduction of PRSV inocula in Pune, because infected