PHYTOTOXICITY OF CANOLA RESIDUES - RELEASE OF WATER-SOLUBLE PHYTOTOXINS

Phytotoxicity of root, stem and leaf residues of canola (Brassica napu s L.) was studied in a laboratory incubation for 8 wk. Bioassays were conducted with corn (Zea mays L.), barley (Hordeum vulgare L.) and whe at (Triticum aestivum L.) seeds to determine the relative toxicity of residue extracts. The release of volatile fatty acids (VFAs) and pheno lic compounds (PCs) during incubation was studied to assess the role o f these compounds in phytotoxicity. Canola residue extracts significan tly inhibited (P less than or equal to 0.01) seedling growth (coleopti le and radicle lengths) of all crop species tested, with leaf and root residues causing the greatest and least toxicity, respectively. Incub ation temperature had no impact on the toxicity of extracts. All resid ue extracts had VFAs prior to and during the incubation, with leaf res idues producing relatively high levels of VFAs. The release of VFAs de clined drastically during the incubation period. The release of PCs, m easured as total phenolic compounds in extracts, was highest in leaf r esidues and remained higher than those of root or stem residues. Toxic ity of residue extracts was not related to the amounts of VFAs and PCs found. However, toxicity appeared to be most related to the presence of total phenolic compounds in residue extracts.