In-vitro study of toxicity of soluble sulphides to three nematodes parasitic on rice in ,Senegal

L. Toxicity of sulphides to three species of nematodes parasitic on rice from Senegal (Hirsch” n i e h oryzaë, H. spinicandata and Tyleizchorhyizckvs irnashhoodi) was studied in vitro using three different methods. A Sulphide Time Unit (STU) was defined related to the average concentrations of sulphides and their variations during the tests. With hydrogen sulphide dissolved in water, the very low pH increased nematode mortality. When hydrogen sulphide was dissolved in a buffered medium used for bacterial culture, mortality was lower but a shock effect appeared due to sudden contact with high concentrations of sulphides and toxicity of some of the components of the medium. When hydrogen sulphide was produced by sulphate reducing bacteria a similar shock effect was still observed, but only when high concen-trations were reached within 1 or 2 days: in such experiments nematodes were killed by low STU, and differences were observed in resistance of the three species. However, when sulphide accumu-lated more slowly, i.e., when lethal concentrations were reached in 3 or more days, the sensitivity of the three species was similar: 50 % mortality was obtained at about 120-130 STU. The possibility of using sulphate reducing bacteria for biological control of parasitic nematode