Evaluation of allelopathic effects of Coriandrum sativum L.

Allelopathy has been exploited as a weed control tool in order to reduce the use of herbicides and improve weed management strategies, both in the integrated and organic farming systems. Interesting results were obtained by selecting allelopathic crop types, using allelopathic cover crops and developing herbicides from allelopathic compounds. Herbicides derived from allelopathic compounds may have new target sites, important in managing herbicide resistance. Many crops have been observed to have allelopathic activity. In particular, Coriandrum sativum L. was found to have allelopathic properties, although available results are few and without practical relevance. The aims of this study were to evaluate allelopathic potential of different plant tissues of C. sativum at different growth stages and their activity against wheat (Triticum aestivum L.), Lolium multiflorum Lam., Amaranthus retroflexus L. and Conyza canadensis (L.) Cronquist respectively one of the main cereal crop and three most problematic weeds worldwide due to their herbicide resistance. Plants of C. sativum were collected at flowering and at harvest stage in central Italy, divided in leaves, stems and roots tissues, dried, ground to a fine powder, soaked in distilled water for 24-h and then filtered obtaining aqueous extract (25% w/v). Petri dishes bioassays were carried out with leaves, stems and roots aqueous extracts of C. sativum (0, 2.5, 5, 10, 17.5 and 25% w/v concentrations) in order to compare their effect on seed germination and seedlings growth of Sinapis alba L., used as test specie. Subsequently, aqueous extracts of aerial biomass (stems + leaves) of C. sativum were applied in Petri dishes bioassays against wheat, L. multiflorum, A. retroflexus and C. canadensis. Fifty seeds of each species were treated with the six-extract concentrations mentioned before, placing Petri dishes in a growth chamber in a completely randomised design with three replications. Germination percentage, radicle and hypocotyls lengths were determined. Data were subjected to a non-linear regression analyses by using a dose-response model and the EC50 and EC90 levels (Effective Concentration) were derived. EC levels showed that the extracts from roots had a lower inhibitory effect on seed germination, radicle and hypocotyls length of S. alba than leaves and stems extract and their allelopathic activity was higher at flowering stage than at harvest stage. The extract of aerial biomass did not affect germination of T. aestivum, but inhibited seed germination and growth of the tested weeds. These laboratorial results pointed to the possibility to use C. sativum allelopathic potential in practical relevance, in order to reduce the use of herbicides and improve the management of herbicide resistant weeds. Nevertheless, studies under field conditions are needed.