Abstract
Eighty species of bacteria belonging to eleven genera, about half of which were plant pathogenic, were tested for their ability to produce coronatine, a new physiologically active substance reported previously to be produced by Pseudomonas coronafaciens var. atropurpurea. Other than this bacterium, only two Pseudomonas species, P. morsprunorum and P. maculicola, were found to produce coronatine.
Mutants of P. coronafaciens var. atropurpurea lacking the ability of producing coronatine, which were obtained during successive cultures of a virulent wild strain, were not pathogenic on Italian ryegrass, the host plant of the bacterium. Considering the fact that coronatine is a phytotoxic substance, this substance should be indispensable for developing symptoms of halo blight. Coronatine, however, would not be the sole substance governing the mechanism of pathogenicity in P. coronafaciens var. atropurpurea, because P. morsprunorum and P. maculicola were not pathogenic on Italian ryegrass although they produce coronatine.
