By Julianna Kettlewell
BBC News Online science staff
World cocoa production could decline if diseases ravaging South American crops spread to other major cocoa producing regions, UK scientists have warned.
A cocoa pod with the frosted appearance of frosty pod disease
Tens of thousands of people have lost their jobs as the cocoa industry struggles with the "witches' broom" and "frosty pod" infections.
If the diseases reach plantations in West Africa the effects could be devastating, researchers claim.
Their concerns are detailed in the summer edition of Biologist magazine.
"In Bahia [on the Atlantic coast of Brazil], the destruction caused by witches' broom disease (WBD) has been terrible," co- author Dr Gareth Griffith, of the University of Wales Aberystwyth, told BBC News Online.
"It is estimated that 200,000 people have been put out of work, and a further two million people have been indirectly affected," he continued. "The knock-on effects have included a soaring crime rate and extensive rural depopulation."
Opportunity to spread
WBD and frosty pod disease (FPD) are both fungi and close relatives of one another.
WBD causes the growing parts of cocoa trees to become swollen and branched, giving the appearance of a witches' broom.
FPD, on the other hand, only attacks the growing pods. The fungus produces cream-coloured spores, which sit on the pod surface leaving a frosty dusting.
Cocoa leaves suffering from the effect of witches' broom disease
WBD and FPD were first identified in the early 20th Century. According to Dr Griffith, they probably evolved in the Amazon rainforest.
It is likely they simmered away at stable endemic proportions - until, that is, increased trade and cocoa production gave them a golden opportunity to spread.
Dr Griffith believes growers travelling from one region to the next probably took the diseases with them.
"People take what they think are healthy pods and try to plant them in a new area - but they can accidentally bring the disease with them," he explained. "That's how WBD got to Ecuador and that is almost certainly how it got to Bahia."
Once WBD becomes established in a cocoa crop, the yield can decrease by up to 90%. And, despite a century of research, no one has come up with a very effective control strategy.
Current battle plans include developing a resistant strain of cocoa plant.
"In Bahia they are focusing on developing a resistant strain, because there the crops were totally devastated," said Bob Eagle, of Cocoa Research UK. "So they have the opportunity to look for cocoa plants that grow in spite of the disease, to see if there is some natural resistance that one can build on."
South America is not the world's biggest producer of cocoa. It contributes only about 10% of the total quantity reaching the global market.
The giant producer is Africa, which churns out more than half of all cocoa.
Dr Griffith fears that if WBD and FPD reach West Africa the results could be catastrophic.
"In West Africa there are millions of families who depend on cocoa," he said. "This disease could devastate their livelihoods."
Dr Griffith would like preventative measures to be taken before it is too late.
"People have a habit of closing the stable door after the horse has bolted," he said. "I am trying to avoid the situation being the same here."
However not everyone involved in the cocoa trade is so worried.
Dr Griffith fears that if the diseases reach West Africa the results could be catastrophic
"We would be concerned if we thought there was any serious risk of WBD getting into West Africa," said Mike Webber, director general of the Biscuit, Cake, Chocolate and Confectionery Association.
"There is a very strict quarantine system for any material moving from one cocoa region to another.
"The plants are quarantined for literally months - and only if they are healthy can they move on."
Dr Griffith is not so confident. He is calling for a full risk assessment, to work out the chances of these diseases making it to Africa.
"Increased air travel and crop miles mean that the risk - although small - is growing," he said. "Something needs to be done now before it is potentially too late."