An isolation and screening procedure was developed to identify soil actinomycetes that can produce germination and growth inhibitors on agar plates. Eight of 120 isolates tested demonstrated severe toxicity on cress (Lepidium sativum L. ‘Curly’) and barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG]. Several isolates were observed to stimulate growth. In replicated tests using the agar screening procedure, compounds produced by microorganisms significantly inhibited germination and growth of indicator plants. Organisms shown to produce toxins in agar media did not always produce toxins when grown in submerged culture.
