Barren ring, a description and study of causal relationships

A description is given of a rare soil disease, called "barren ring", which occurs in some old, deserted pastures. It is an expanding ring-shaped area of diameter up to 17 meters in which the vegetation is killed. Regeneration of normal vegetation occurs in the center of the ring. A number of microorganisms were isolated from the barren soil and tested for phytotoxicity in vitro. Of 24 pure strains of bacteria and fungi isolated, only one bacterium showed phytotoxicity to the test organism, Phleum pratense L. It was identified as a strain of Pseudomonas aureofaciens Kluyver. Bioautography of extracts of the bacterial culture showed that there are two compounds extractable in benzene which have both antibiotic and phytotoxic activity. However, it has not been established that this bacterium is the sole causal agent of the disease and it is suggested that it is caused by an association of microorganisms.