Medicinal plants with phytotoxic activity harbour endophytic bacteria with plant growth inhibitory properties

Abstract

The cultivable endophytic bacteria associated with two medicinal plants Hypericum perforatum L. and Ziziphora capitata L. contrasting with phytotoxic activity were investigated. The phytotoxic activity of plant extracts, and bacterial metabolites on seed germination and seedling growth of tomato were evaluated. In comparison to Z. capitata, the extract of H. perforatumcontains a higher content of phenolic compounds. The crude extract of H. perforatum inhibited germination of seeds and seedling growth of tomato, whereas Z. capitata extracts only slightly reduced these parameters. Interestingly, almost half of the endophytes associated with H. perforatum had an inhibitory effect on plant growth, whereas rarely any plant inhibitory effect was found among isolates from Z. capitata. All bacterial isolates from Z. capitata were able to stimulate plant growth, by 35–80%. In contrast, only five isolates from H. perforatum caused significant improvement in plant growth (22–46%). The results showed that medicinal plants with higher phytotoxic activity were colonized with endophytic bacteria which inhibit plant growth and development. These findings indicate that plant phytochemical constituents and activity determine the physiological properties of their endophytes.