Agriculture Reference
In-Depth Information
by the Thai Department of Agriculture focused on the immediate eradication of
infected trees, but this strategy met with limited success due to the reluctance of villag-
ers to destroy any papaya trees even with minimal fruit-bearing potential (Thitiprasert
2003).Becauseoftheburdenofdisease,averageyieldfrompapayacultivationfellsig-
niicantlyfromthe1980stothe1990s,whilethepriceperkilogrammorethandoubled
nationwide(Napasintuwong2009).Papayaareaundercultivationandoveralltonnage
producedcontinuedtofallby50 percentbetween1997and2006.Giventheimportance
of papaya both in Thai culture and in the nutritional well-being of ordinary Thai people,
PRSV had by this time been identified by the Thai authorities as an agricultural threat of
national importance.
There was obvious potential, therefore, for the approach using transgenic
pathogen-derived resistance in papaya developed for Hawaii to be also applied in
Thailand. Thailand also seemed a promising location because the country had already
establishedareputationasaleaderinbiotechnology: from1992to2000,fortygeneti-
cally engineered crops were approved for study in Thailand, and the Thai government
hadinvestedheavilyinbuildingnationalcapacityforbiotechnologyfromthe1980s
onward(Sriwatanapongseet al.2007).hailandalsohadexpertpersonneldirectlycon-
cerned with the protection and promotion of papaya cultivation. One of these, the gov-
ernmentplantvirologistVilaiPrasartsee,hadworkedsincethe1970sattheKhonKaen
Plant Material and Technical Service Center in Khon Kaen, Thailand, a facility located
inoneofhailand'smostimportantagriculturalareas.
Prasartsee was charged with finding a means to control the papaya ringspot virus in
Thailand. With this objective in mind, she forged a collaboration with Dennis Gonsalves
at Cornell University as early as 1981, at first employing non-transgenic approaches to
controlthevirus,thoughwithlittlesuccess.WhenGonsalves'sgroupinallybeganto
make headway back in Hawaii by applying a transgenic PDR approach to virus con-
trol, Prasartsee and her team moved quickly to replicate the approach for Thailand.
The effort would be more complex than simply importing Hawaiian transgenic papaya
seeds,however: hesweet,yellow-leshed,palm-sizedHawaiianvarietiesareneither
adapted to Thai growing conditions nor acceptable to Thai consumers, who look for
largezucchini-shapedvarietiesbredfor som tam .
The Thai researchers therefore had to separately transform their own locally grown
Thai papaya varieties with the coat protein gene isolated from Thai strains of the
virus.hisworkbeganin1995,when,withmodestfundsfromthehaiMinistryof
AgricultureandCooperativesandtheUnitedStatesAgencyforInternationaldevelop-
ment(USAID),PrasartseearrangedfortwoofhercolleaguestogototheGonsalves
laboratory at Cornell University with the aim of creating a transgenic, virus-resistant
papaya. The researchers took with them isolates of PRSV from Thailand and their own
papayamaterialtotransform.Justtwoyearslater,theyhadsuccessfullytransformed
two Thai-preferred papaya varieties and returned home with the new transgenic plants.
The new virus-resistant papaya could not be released straight away, however, because
of the need to demonstrate safety and lack of environmental harm for a transgenic plant
to satisfy the regulatory process. Tests showed that the virus resistance trait was passed
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