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VIRUSES, SWEET POTATO - PAPUA NEW GUINEA, SOLOMON ISLANDS

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Scientists are working to save the sweet potato industry in Papua New 

Guinea (PNG) and the rest of the South Pacific. The vegetable is the 

staple food of many islanders, whose crops are declining because of 

viruses that cut yields. The Solomon Islands was also seeking 

assistance in controlling the problems.



Sweet potato research specialist Eric Coleman (Queensland Primary 

Industries Department, Australia) has been in the PNG highlands as 

part of a AUD 2 million (USD 1.6 million) project to identify the 

cause of the insidious yield decline.



Mr Coleman said PNG had an amazing variety of sweet potatoes, which 

had been attacked by some of the 22 known viruses that could affect 

the vegetable. "As you get more viruses, the sweet potatoes get 

longer, skinnier, and uglier," he said. "We have done a lot of 

domestic work to improve the quality of the sweet potato. That is 

because we have removed viruses and delivered a product to farmers 

who plant a material that is basically disease free."



Identifying genes that could make sweet potatoes disease resistant 

was an 'elusive' process to this point, so the emphasis had to be on 

removing viruses. "What we are trying to do in PNG, where there are 

thousands of varieties, is apply our techniques which can identify 

those 22 viruses," he said.



"We are centering the work in the highlands because everyone there 

grows sweet potato or yams. I am fairly sure our technology -- the 

way we identify and remove viruses -- will work. But no one has 

really assessed what viruses are there. We could find viruses we do 

not know about." Mr Coleman said.



"Australians consume 2 kg (4.4 lb) sweet potatoes per person per 

year. In PNG the per capita consumption is 500 kg (1102 lb). I think 

that puts the urgency of this exercise into perspective," Mr Coleman said.



--

J. Allan Dodds





[Sweet potato (_Ipomoea batatas_) is among the major food crops in 

the world and is cultivated in all tropical and subtropical regions 

particularly in Asia, Africa, and the Pacific. Although weevils are 

the most damaging problem of sweet potato worldwide, diseases caused 

by viruses follow closely in importance. Food security in the Pacific 

region is based on the local staples of taro, yams, breadfruit, and 

sweet potato. It is becoming one of the major issues there, both at 

the national and household level, while the traditional "food 

gardens" of the Pacific Islands are disappearing.



Multiple viral infections are common in field plants with the 

potential for synergism (symbiotic enhancement) or cross-protection 

(competitive suppression). Synergism is characterised by a much more 

dramatic increase in symptom severity and virus amounts than could be 

expected by simply adding up the effects of the partner viruses (for 



chlorotic stunt virus_ (SPCSV, genus _Crinivirus_); _Sweet potato 

feathery mottle virus_ (SPFMV), _Sweet potato latent virus_, and 

_Sweet potato mild speckling virus_ (all genus _Potyvirus_); _Sweet 

potato mild mottle virus_ (genus _Ipomovirus_); _Cucumber mosaic 

virus_ (genus _Cucumovirus_); Sweet potato chlorotic fleck virus and 

C-6 virus (both putative members of the genus _Carlavirus_).



Co-infection of SPCSV with SPFMV results in sweet potato virus 

disease (SPVD), a synergistic disease that causes a yield reduction 

of up to 60 percent. The yield losses reported might even be 

underestimated because symptomless plants may not necessarily be 

virus-free and these latent infections may have a yield decreasing 

effect. Synergistic diseases involving some of the other viruses have 

also been reported, and an experimental yield increase of at least 40 

percent has been observed in tested virus-free cultivars of sweet 

potato. The epidemiology of the synergistic viruses and their 

respective vectors will necessarily be highly complex.



In addition to the viruses reported so far, further viruses (possibly 

including new species) can be expected to exist in sweet potato due 

to the predominantly vegetative propagation of this crop, which 

increases the risk of a build-up of viruses. Virus-free planting 

material will need to be provided to farmers regularly since 'clean' 

plants may become infected in the field.



Maps



Pictures



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- Mod.DHA]



Sweet potato chlorotic stunt virus, sweet potato - USA (NC) 20070420.1291

2006

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2004

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Sweet potato viruses - Spain 20040404.0929

2003

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Sweet potato leaf curl - Peru 20030104.0020

1997

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Food security in the Pacific 19970708.1457]

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