Tree Biology

Rubber, Hevea brasiliensis, is an important tree crop throughout the tropics for latex and wood production. For years, rubber producers have wrestled with a mysterious disease, bark necrosis, that caused trees to stop producing latex. The cause was thought to be a bacterial or virus infection. French scientists in Ivory Coast have identified the cause as bulldozers. Bulldozers used to control weeds cause soil compaction and root injury, and restrict water flow to the tree. The resulting water stress damages cells in the stem-root graft, and the damaged cells release cyanide. Cyanide is a normal defensive chemical in rubber and some other trees. When the trees are tapped for latex, cyanide can move from the graft toward the cut, killing the latex-producing cells. Source: designerz.com, from AFP.

This is interesting for several reasons. Soil compaction is a common cause of stress and decline in urban trees. Rubber trees appear to suffer from similar problems when soil is compacted. The mechanism is surprising. We usually think of plants as being tolerant of their own defensive chemicals, but cyanide is always toxic to cells. Linking the release of cyanide to soil compaction is elegant research. In the hunt for plant diseases, management practices should always be carefully examined.