The rubber tree, Hevea brasiliensis, is cultivated in many humid tropical countries for the latex it produces, from which is extracted natural rubber mainly used by the tyre industry. Asia alone provides almost 95 % of the world production, where the first producer is Thailand whose rubber industry earns a regular income for 10 % of the population. However, a disease is attacking rubber trees that causes irreversible drying-up of latex flow, and can affect up to 30% of trees in African, Asian and American plantations, causing marked falls in production and substantial economic losses. Termed “rubber tree bark necrosis syndrome” (RTBN), it was diagnosed in 1983 (4) in an industrial-scale plantation estate (Michelin company, Ivory Coast) by IRD researchers. The first investigations, conducted at the request of the plantation company, could not establish a link between RTBN and any pathogenic agent (fungus, virus, bacterium or mycoplasm).
Further research projects were launched at the end of 1999 by the IRD team and its partners (2) at the request of the rubber production sector and with its support (1). This complex syndrome was then tackled using a multidisciplinary approach (involving plant pathology, agricultural soil science, cell and molecular physiology, virology, and so on) and focusing on several different localities (3), which provided conditions for identifying its origin and activating mechanism.
Since the 1970s, the predominant basis of rubber cultivation has been propagation by grafting on tree stock. In 90% of cases, RTBN attacks the tree vascular tissues, starting right at the grafting point situated in the transition zone between the trunk and the roots, the collar. The first stage of the disease is not detectable because the first cells to undergo necrosis are located in internal tissues of the bark. The necrosis, however, extends steadily to the whole base of the trunk before travelling upwards, up to the tapping notch. At this stage, the notch no longer produces latex and the affected trees are then noticeable. When the outer bark becomes diseased, cracks begin to appear starting from it and then dead parts flake off.
Marie Guillaume | alfa
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