Secondary metabolites from the invasive Solidago canadensis L. accumulation in soil and contribution to inhibition of soil pathogen Pythium ultimum

We conducted field and pot experiments to test whether total flavones, total phenolics, and total saponins released from Solidago canadensis L accumulate and persist in soil, and whether these chemicals can explain the allelopathic effects of this plant on a soil pathogen. As S. canadensis grew and its population density increased in the field (experiment 1) and pot (experiment 2) experiments, soil concentrations of total flavones, total phenolics, and total saponins increased with increasing density of S. canadensis. In our experiment 3, the activity of the soilborne pathogen Pythium ultimum was 22.62% lower in soil conditioned by S. canadensis than in non-conditioned soil. The concentrations of total flavones, total phenolics, and total saponins in soil negatively correlated with P. ultimum activity. In the experiment 4, persistence of total flavones, total phenolics, and total saponins was higher in sterilized than in non-sterilized treatment regardless of soil types. Despite of degradation in non-sterilized soil, the three compounds kept stable 6 days after incubation. These results show that total flavones, total phenolics, and total saponins released from S. canadensis accumulate in soil. The concentrations of these secondary metabolites negatively correlated with disease severity of tomato, suggesting that these secondary metabolites contribute to the allelopathic effects of S. canadensis on the soilborne pathogen P. ultimum. (C) 2011 Elsevier B.V. All rights reserved.