Allelopathic interactions of brown mustard (Brassica juncea L.) with other aromatic plants during germination and seedling development

Organic compounds originating from plant metabolism and reaching the environment may inhibit or stimulate germination and early developmental processes of other plants grown in the vicinity. The aim of this study was to investigate the allelopathic interactions of brown mustard with four other aromatic plants (summer savoury, coriander, caraway and common sage). While health-promoting metabolites of brown mustard are thoroughly investigated and the plant receives an increasing interest from cultivators of aromatic and medicinal plants, its allelopathic interactions with other aromatic plants are poorly documented. The experiments were performed in closed germination vessels, under controlled conditions. The influence of the presence or absence of light, as well as of a sufficient or reduced water supply on the co-germination of brown mustard seeds with each of the other four aromatic plants was also evaluated. The presence of brown mustard reduced the germination velocity of caraway, coriander, sage and savoury. It inhibited stem elongation, but stimulated root growth of savoury. Shoot growth of coriander seedlings was enhanced by the vicinity of brown mustard plantlets. Caraway slowed down the germination of brown mustard seeds, but it stimulated root and stem elongation of the seedlings. The presence of savoury enhanced the fresh biomass production of brown mustard. Common sage inhibited root growth, but stimulated stem elongation of brown mustard plantlets. Most of the allelopathic effects were more pronounced under water shortage than under sufficient water supply. Positive interspecific influences on biomass production were, in most cases, more pronounced in the presence of light. The findings may contribute to optimization of brown mustard cultivation in small parcels, in the vicinity of other aromatic plants, some allelopathic interactions being able to stimulate growth and developmental processes in an environmental-friendly and cost-effective manner.