Agriculture Reference
In-Depth Information
oftherecommendeddailyintake(RDI)ofvitaminCforanadultand33 percentofthe
RDI for vitamin A (Duxbury 2003). hus, although it receives little attention from
development experts concerned with food security, papaya already helps alleviate two
of the “big three” micronutrient deficiencies that plague undernourished people glob-
ally(iron,vitaminA,andiodine)andclearlyholdsconsiderablepromiseforfurther
diversifying the diet of the rural poor in tropical countries.
Inhailandpapayahasspecialculinaryandculturalimportance.Itistheprimary
ingredient in
som tam
(greenpapayasalad),whichisconsumeddailybyordinaryhai
people—especiallyruralpeopleworkinginthepaddyieldswhereasharedbowlof
som
tam
complementsthestickyricestaple.Morethan90 percentofpapayaconsumedin
Thailand is grown in Thailand, much of that at the household scale in backyard gardens
orperipheralareasaroundricepaddyields(Davidson2008).
Papaya Ringspot Virus
Papayaringspotvirus(PRSV)belongstothegenus
Potyvirus
, and it has a single-stranded
RNAgenomeencapsidatedbythegenome-encodedcoatprotein(CP)(Tripathiet al.
2008).PRSVisavector-bornepathogen,mainlytransmittedbyaphids.Symptomsof
infection typically include characteristic ringspot symptoms on the fruits of infected
trees as well as chlorosis on leaves and the stunting of affected plants.
Althoughirstreportedin1945,PRSVmayhavebeenobservedasearlyas1937on
theislandofOahuinHawaii.Initiallyarelativelymildpathogen,PRSVevolvedamore
virulentstraininthe1950s,virtuallywipingoutthepapayaindustryinOahubythe
late1960s.AroundthistimetheviruswasirstdetectedinBrazil,theworld'slargest
papaya producer, and it gradually forced the entire papaya industry to relocate inland
awayfromtheinitialgrowingareasaroundSãoPaoloandRiodeJaneirotomorepris-
tineuninfectedareasintheremoterwestofthecountry(Gonsalves1998).InTaiwan,
PRSVhadspreadthroughouttheentireislandbythelate1970s,devastatingtheproduc-
tionindustry.Itwasdiscoveredin1991inQueensland,Australia,thecenterofpapaya
production in that country, and it is now considered a worldwide problem with no pro-
ducer country being free of the virus.
Various mitigation strategies have been attempted in different regions with vary-
ingdegreesofefectiveness.InTaiwan,forexample,thedestructivenessofPRSVhas
forced farmers to grow papaya as an annual crop, with trees removed immediately
atertheharvestoftheirstmaturefruit,bywhichtimetheywillusuallyhavebecome
infected.InTaiwansomefarmershavealsoadoptedtheexpensivestrategyofgrowing
papayaunderprotectivenetstoexcludeaphidsuntilirstfruitproduction.InBrazil,a
vastlylargercountry,thekeygrowingareashavecontinuallyshitedtotrytokeepone
step ahead of the spread of the virus. However, this has raised shipping costs and low-
ered the quality of the fruit, which is fragile and easily damaged during transportation
(Gonsalves1998).
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