French scientists bounce light on rubber disease

25th March 2005, Comments 0 comments

PARIS, March 24 (AFP) - French experts said Thursday they had found the key to a disease that widely affects commercial rubber trees and hits producers deeply in the pocket.

PARIS, March 24 (AFP) - French experts said Thursday they had found the key to a disease that widely affects commercial rubber trees and hits producers deeply in the pocket.

Rubber tree bark necrosis, which first came light in Cote d'Ivoire in 1983, causes the latex sap, tapped by a cut made on the tree's trunk, to dry up. For years, scientists have wondered if the disease was caused by a germ or a virus, perhaps transmitted by an insect or even the blade used by plantation workers to make the tapping cut.

But a multi-discipline team from France's Institute for Development Research (IRD) and other agencies has found after exhaustive detective work that there is a far simpler but quite unexpected cause: the bulldozer.

The scientists noticed that trees with bark necrosis often had poorly developed root systems and were invariably located near plantation paths used by bulldozers, IRD said in a press release.

They discovered that the bulldozer tracks compacted the earth, often preventing water, which also carries vital salts, from seeping through the soil to reach the roots.

The stress from this water shortage, which can be compounded during dry seasons, has a dramatic - but initially invisible - effect on young rubber trees, which since the 1970s are usually grafts placed on existing trunks.

The stress kills cells at the join between the graft and trunk. This has a ripple effect among adjoining cells, destroying cellular walls and releasing large quantities of cyanide, a poison that naturally occurs in rubber tree tissues.

When the cut is made to produce sap, the rubber tree sucks up more water from the soil, and this helps the cyanide to spread upwards, gradually sickening all of the bark.

© AFP

Subject: French News

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