BEHAVIOR OF DIFFERENT HORTICULTURAL SPECIES IN PHYTOTOXICITY BIOASSAYS OF BARK SUBSTRATES

The use of forestry wastes (barks, sawdust, wood chips) as potting med ia components can involve serious problems of toxicity that must be ev aluated. Evaluation methods may consist of analytic techniques to dete ct and quantify phytotoxic molecules, or rapid bioassays, with low tec hnical requirements, using species sensitive to the toxic elements. Th ese bioassays should be able to predict plant behaviour in real growin g conditions. In this study we used as substrate cork oak bark (Quercu s suber L.). This material, like other forestry wastes, contains phyto toxic phenolic compounds which can be washed out with hot water, The p henolic content of cork (C) and washed cork (WC) was measured, and two germination bioassays were carried out with eight horticultural speci es, In the first, aqueous extracts of cork (C) and washed cork (WC) ob tained with water at 15 degrees C and 70 degrees C were used, and the second was done directly on the substrates. In addition, a seedling gr owing test was carried out with the same species. We concluded that to mato and lettuce are the most sensitive species, and the direct test o n the substrate is recommended owing to its simplicity and close corre spondence to growing conditions.