Allelopathic prospective of Ricinus communis and Jatropha curcas for bio-control of weeds

Abstract

Ricinus communis and Jatropha curcas (Euphorbiaceae), two biodiesel plants are especially well known for many industrial, pharmacological, and/or toxicological properties, but to date very little is known about their allelopathic characteristics. Hence, to explore the allelopathy of both plants, the aqueous methanol extracts of their leaves were examined at five different concentrations (3-, 10-, 30-, 100-, and 300-mg dry weight [DW] equivalent extract/mL) on the seedling growth of cress, lettuce, alfalfa, Italian ryegrass, barnyard grass, and crabgrass, and on the germination of cress and barnyard grass. The bioassay experiments were conducted in a completely randomized design with three replications. The inhibitory activities of both extracts depends on the concentration and test plant species. Considering the I50 values, the seedling growth of lettuce was most sensitive to both extracts and barnyard grass was least sensitive. At concentration of 300-mg DW equivalent extract/mL, R. communis completely inhibited the germination of both cress and barnyard grass, and the seedling growth of cress, lettuce, Italian ryegrass, and barnyard grass. At the same concentration, complete inhibition on the germination of cress and the seedling growth of lettuce and alfalfa was only observed by J. curcas extracts. These results suggest that both plants have allelopathic properties and may possess allelochemicals. Since R. communis extracts had greater activity than J. curcas against the major crop weeds, this plant could be the best candidate for isolation and identification of allelochemicals, which might promote the discovery of new natural herbicides for sustainable agriculture.