Allelopathic Effects of Aqueous Extracts of Ricinus communis L. on the Germination of Six Cultivated Species

Aims: The effect of aqueous extracts of castor bean (Ricinus communis L.) On the germination of six cultivated crops was investigated.
Study Design: Samples of R. communis were harvested from the region of Gabès (south of Tunisia) and tested at laboratory on crops seeds.
Place and Duration of Study: Regional station of Gabès- National Institute of Research in Rural Engineering, Waters and Forests – Tunisia, between October and December 2014.
Methodology: Extracts were obtained after an incubation of 9 g of dry plant material (powder) in 100 ml distilled water during 48 hours at 60°C. The extraction was made from five parts of R. communis (root, twig, leaf, seed and pericarp) and used in germination tests.
Results and Conclusion: Results showed two types of behavior: the aqueous extracts of root, twig, and seed had a low effect of inhibition for all studied species. The aqueous extracts of leaf and pericarp had a high effect of inhibition. C. olitorius is the most tolerant species; its germination rate is 99, 99, 97, 96, 69.5 and 53.5% for aqueous extracts of root, twig, seed, leaf and pericarp respectively. L. culinaris is the most sensitive species; its rate of germination is 97, 68.5, 44, 3 and 0% for aqueous extracts of root, twig, seed, leaf and pericarp respectively. Leaf and pericarp aqueous extracts are the most inhibitive of germination resulting in germination rates lower than 16.5% for all studied species, except for C. olitorius, its germination rate is 69.5 and 53.5% with pericarp and leaf extract respectively. The aqueous extracts of R. communis inhibited root length in all studied species, essentially with the aqueous extracts of leaf and pericarp. These two parts of R. communis showed high allelopathy effect in percentage of germination and root length for all studied species.