Allelopathic effects of Jatropha curcas on marigold (Tagetes erecta L.)

The allelopathic effects of leaf leachates and residues of Jatropha curcas amended into soil were determined on the growth, relative membrane permeability (RMP) and the proline content of marigold (Tagetes erecta) seedlings. The application of leaf leachates of J. curras in the soil significantly inhibited the shoot and root length of marigold compared to unamended soils. The leaf leachates increased the RMP and proline content in the roots of marigold seedlings. The leachates concentrations did not influence the soil pH, however their 75 and 100% concentrations increased the soil electrical conductivity (EC) by 128 and 215%, respectively, over the control. Similarly the J. curcas residues incorporated into soil, were more phytotoxic to the foot than shoot growth of marigold seedlings. During the decomposition, RMP was increased from 37.11 to 56.72% and prolific from 19.68 to 37.66 mu mol(-1)fw. In the soil incorporated with the residues, the phytotoxicity to growth, RMP and prolific content in the seedlings increased with increasing amount of residues incorporated and decreased over time. During the decomposition, (lie electrical conductivity (EC) varied with magnitude of inhibition, whereas, pH was not correlated to inhibition. These results showed that J. curcas released the phytotoxic compound(s) into soil, which were inhibitory to certain test species.