Baicalin released from Scutellaria baicalensis induces autotoxicity and promotes soilborn pathogens

Experiments were conducted to determine whether allelochemicals released by the important medicinal plant Scutellaria baicalensis Georgi help to explain why S. baicalensis performs poorly when continuously cropped. Based on high performance liquid chromatography, the concentration of baicalin (the major compound released by S. baicalensis roots) in the soil where S. baicalensi had been grown for 3 years was 0.97 microg x g(-1). Both the crude extracts from S. baicalensis roots and purified baicalin at 0.97 microg x g(-1) increased the mortality of S. baicalensis seedlings in an autotoxicity test. This concentration stimulated the growth of two soilborne pathogens (Pythium ultimum and Rhizoctonia solani) on agar, and their growth and pathogenic activity in sand. Seedling mortality and damping-off caused by both pathogens were greater in sand where S. canadensis had previously grown than in sand where it had not previously grown. Mortality and damping-off of S. baicalensis seedlings also were significantly higher in soil collected from an S. baicalensis field than in soil collected from a Nicotiana tabacum L. field. The results are consistent with the hypothesis that allelochemicals released by S. baicalensis negatively affect S. baicalensis directly by inducing autotoxicity and indirectly by increasing pathogen activity in the soil.