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Department of Plant Protection, College of Agriculture, University of Baghdad, Iraq AND Department of Botany, University of Kuwait

Abstract

Field observation of a stand of Eucalyptus microtheca indicated a clear reduction in growth of herbaceous species under its canopy, although the same herbaceous species grow well under adjacent trees of casuarina cunninghamiana. This project was undertaken to deduce whether reduction in growth was due to competition or to allelcpathic effects. The results indicate that soil moisture, nutrient elements, and shading were not the causative agents for inhibition. On the other hand, leaf extracts, decaying green and brown leaves, and soil collected under Eucalyptus canopies inhibited seed germination and seedling growth of associated species. Initial studies indicate the presence of phenolic acids and volatile compounds, which are believed to play a role in growth inhibition.