COUMARIN AS A SELECTIVE PHYTOCIDAL AGENT

Abstract

THE recent discovery^1,2 that synthetic plant-growth substances such as 2 : 4-dichlorophen-oxyacetic acid have selective phytoeidal actions in very low concentrations has opened up a new field of investigation into their mechanisms of action. The search for new molecules with similar properties has been intensified. The fact that unsaturated lactone groupings are frequent features of naturally occurring substances having inhibitive effects on cell-growth^3,4,5 revives interest in the phytocidal activity of the common plant metabolite, coumarin. This substance was, apparently, first shown by Klebs⁶ to be toxic to Algæ, and later by Schreiner, Reed and Skinner⁷ to have inhibitive effects on the growth of wheat. Cameron⁸, in a discussion on soil fertility, referred to the fact that both coumarin and daphnetin prevented the development of wheat, and Sigmund⁹ noted the effects of daphnetin and æsculetin on seed germination. In 1934, Köckemann¹⁰ gave the term 'blasto-choline' to material of unknown structure, present in ripe fruits, which suppressed germination of cress seeds. Since then it has been shown^11.12,13 that a number of unsaturated lactones, including coumarin, parasorbic acid and B-angelicalactone have blastocholine effects, suppressing germination of seeds at concentrations such as 100 parts per million. The concentrations at which the lactones are effective have been considered to be much higher than those which bring about comparable effects with 2 : 4-dichlorophenoxyacetic acid.