Toxicity of Cassava Cyanogens to the Root-Knot Nematode, Meloidogyne incognita (Kofoid and White)

Aqueous extracts of cassava roots showed marked nematicidal activity against the root-knot nematode Meloidogyne incognita. These extracts contain significant amounts of cyanogenic compounds viz., linamarin and its degradation products, acetone cyanohydrin and cyanide. In vitro studies on the effect of cassava cyanogens on second stage juveniles of M. incognita showed that both cyanide and acetone cyanohydrin displayed significant and similar nematicidal activity. The toxicity was related to the concentration of these compounds and the exposure time. Linamarin by itself was nontoxic but addition of linamarase released cyanide/acetone cyanohydrin, which produced toxicity. The in vitro activity of cassava root (tuber and rind) extracts was comparable to that produced by sodium cyanide and acetone cyanohydrin, with respect to concentration (cyanide equivalents) and exposure time, indicating that the presence of these compounds in the extracts is the primary factor responsible for nematicidal activity.