Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Causes of rubber tree bark necrosis identified


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.

Previous results prompted a search for pathogenic agents focused on viruses or viroid organisms that could be transmitted by the tapping knife. This line proved unfruitful. Any major influence of soil chemistry characteristics was also excluded. The research team subsequently favoured a hypothesis envisaging a multi-factor physiological cause. Investigations into the influence of the physical constraints of the soil then began. Evidence appeared of a clear correlation between the risks of the emergence of the disease and the strong mechanical resistance of soils which holds up water transport and absorption by the tree roots. This accentuated resistance, which can be the result of low porosity or induration of these soils, appeared here to be more specifically linked to ground compaction by bulldozers. The non-random distribution of diseased trees is consistent with the areas where bulldozer use has been most intense. Physiological observations showed moreover that the rubber trees hit by necrosis have poorer than normal root development. This anomaly, whether a result of poor stock/graft interaction or of genetic predisposition of the stock tree, causes supply of water and mineral salts to the tree to be low. This tendency is accentuated by complications that grafting engenders in the tree’s circulation vessels, particularly in the junction between the different sap-conducting vessels of the graft-carrier and graft. Eco-physiological analyses revealed that the RTBN-affected trees are in a state of water deficit. This is aggravated in times of drought (a climatic factor) or when trees are overexploited for tapping (human factor).

The combination of these different stresses induces necrosis (cell-death) in the collar of the tree, involving the disintegration of cell compartments, and a resulting release of large amounts of cyanide which the rubber tree tissues naturally contain. The effect of this poison, accumulating owing to the impaired metabolism, is to activate the necrosis. Water that rises towards the notch, drawn up by tapping, facilitates the upward diffusion of the cyanide and hence the spread of necrosis towards the upper trunk. The resulting deep disintegration of the trunk phloem and bark tissues explains the irreversible blockage of latex production.

Rubber tree bark necrosis –its appearance and development- therefore results from the accumulation of climatic and human-induced stresses and physiological malfunctions in the grafted trees. This multifactor approach has provided the first overall view of how the disease generates. However, grey areas remain to be explored. A genetic approach is now being applied, with the aim of finding early indicators of the disease that can make field detection as reliable as possible. The results acquired have provided the bases for recommendations on practical measures to take. These are already being applied and are an important new tool in plantation management.

Fabienne Doumenge (Montpellier) - DIC

(1) Institut français du caoutchouc (Paris), Michelin (Clermont-Ferrand), International Rubber Plantation Society (Paris), Socfinco (Brussels), in the context of a research agreement concluded with the IRD n°2454 (1999-2004).

(2) Abobo-Adjamé University (Ivory Coast), Instituto Valenciano de Investigaciones Agrarias (Spain), INRA (Avignon, Bordeaux), Cirad (Montpellier), Poincaré University (Nancy), Mahidol University (Thailand).

(3) Brazil, Cambodia, Cameroon, China, India, Indonesia, Ghana, Liberia, Malaysia, Nigeria, Republic of the Ivory Coast, Thailand.

4) NANDRIS D., CHRESTIN H., GEIGER J.P., NICOLE M. et THOUVENEL J.C., 1984. Occurrence of a phloem necrosis on the trunk of rubber tree. 75th Annual Conference of Rubber Research, Sri Lanka, September 1984, Colombo, in Proceedings p. 59.

Marie Guillaume | alfa
Further information:

More articles from Agricultural and Forestry Science:

nachricht Harnessing a peptide holds promise for increasing crop yields without more fertilizer
25.11.2015 | University of Massachusetts at Amherst

nachricht Study shows how crop prices and climate variables affect yield and acreage
18.11.2015 | University of Illinois College of Agricultural, Consumer and Environmental Sciences

All articles from Agricultural and Forestry Science >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: How do Landslides control the weathering of rocks?

Chemical weathering in mountains depends on the process of erosion.

Chemical weathering of rocks over geological time scales is an important control on the stability of the climate. This weathering is, in turn, highly dependent...

Im Focus: How Cells in the Developing Ear ‘Practice’ Hearing

Before the fluid of the middle ear drains and sound waves penetrate for the first time, the inner ear cells of newborn rodents practice for their big debut. Researchers at Johns Hopkins report they have figured out the molecular chain of events that enables the cells to make “sounds” on their own, essentially “practicing” their ability to process sounds in the world around them.

The researchers, who describe their experiments in the Dec. 3 edition of the journal Cell, show how hair cells in the inner ear can be activated in the absence...

Im Focus: Climate study finds evidence of global shift in the 1980s

Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.

Scientists say that a major step change, or ‘regime shift’, in the Earth’s biophysical systems, from the upper atmosphere to the depths of the ocean and from...

Im Focus: Innovative Photovoltaics – from the Lab to the Façade

Fraunhofer ISE Demonstrates New Cell and Module Technologies on its Outer Building Façade

The Fraunhofer Institute for Solar Energy Systems ISE has installed 70 photovoltaic modules on the outer façade of one of its lab buildings. The modules were...

Im Focus: Lactate for Brain Energy

Nerve cells cover their high energy demand with glucose and lactate. Scientists of the University of Zurich now provide new support for this. They show for the first time in the intact mouse brain evidence for an exchange of lactate between different brain cells. With this study they were able to confirm a 20-year old hypothesis.

In comparison to other organs, the human brain has the highest energy requirements. The supply of energy for nerve cells and the particular role of lactic acid...

All Focus news of the innovation-report >>>



Event News

European Geosciences Union meeting: Media registration now open (EGU 2016 media advisory 1)

01.12.2015 | Event News

Urbanisation and migration from rural areas challenging agriculture in Eastern Europe

30.11.2015 | Event News

Fraunhofer’s Urban Futures Conference: 2 days in the city of the future

25.11.2015 | Event News

Latest News

USGS projects large loss of Alaska permafrost by 2100

01.12.2015 | Earth Sciences

New study reveals what's behind a tarantula's blue hue

01.12.2015 | Life Sciences

Climate Can Grind Mountains Faster Than They Can Be Rebuilt

01.12.2015 | Earth Sciences

More VideoLinks >>>