Valuation of Phytotoxic Activity of Naturally Occurring Phenolic Compounds.

Abstract

Relative phytotoxic activity of 21 phenolic compounds previously reported as allelochemicals was evaluated with aqueous solution test and soil incorporation test. At 1.0mM, aqueous solutions of juglone, coumarin, t-cinnamic acid, o-hydroxy-phenylacetic acid and 3-phenylpropionic acid were most inhibitory to the radicle elongation of lettuce (Lactuca sativa) and Japanese barnyard millet (Echinochloa utilis), followed by salicylic acid, β-resorcylic acid and benzoic acid (Fig. 1). The effect greatly decreased at 0.1mM for all compounds except juglone. Lettuce was more susceptible than E. utilis. The most effective 8 compounds were then incorporated in soil and bioassayed using germinating lettuce (Fig. 2). Inhibitory activity on lettuce radicle elongation was highest in juglone, followed by coumarin, as in the solution test. The effect on 14 plant species of soil-incorporated coumarin and juglone was also determined. Although juglone fatally inhibited radicle elongation of all test species at 2.0μmol/g soil, phytotoxic activity of coumarin at 2.0μmol/g soil differed greatly among the species, and the activity of both compounds at 0.2 and 0.4μmol/g soil also differed among them (Fig. 3). In this case the sensitivity of test plants did not relate to the family of species, but seemed to have some relationships with their seed size. The larger seed species tended to be less sensitive to both compounds, while sensitivity of the small seed species varied over a wide range (Fig. 4).