Abstract
Rough and smooth bacterial colonies were obtained from single lesions on naturally infected leaves of Italian ryegrass and perennial ryegrass. The isolates of both colony types were found to be pathogenic to Italian ryegrass and no difference in intensity of pathogenicity was observed between them. The bacteriological characteristics and the serological reactions of both types of isolates were compared with those of an isolate (P1-6-1) of Pseudomonas coronafaciens var. atropurpurea (Reddy and Godkin) Stapp from Italian ryegrass. Smooth-colony isolates were identical with the isolate P1-6-1, while rough-colony isolates differed in the morphological characters of colonies and the spontaneous agglutination in 2% and 4% sodium chloride solutions. Heated bacterial cells of rough-colony isolates did not react to antiserum made from living whole cells of a smooth-colony isolate of P. coronafaciens var. atropurpurea. From these results, the present isolates were identified as P. coronafaciens var. atropurpurea irrespective of their colony morphology.
Colony types did not change by passing through host plants, nor successive culture on artificial media. All the isolates from halo blight lesions of ryegrasses gave smooth colonies except only two cases in this study. These evidences lead to the presumption that the present rough-colony isolates are the mutants from smooth-colony bacterium occurred in the field and coexisted in a single lesion with the bacterium of wild type. This is the first report not only of rough colony type of P. coronafaciens var, atropurpurea but also of virulent rough-colony bacterium found in a independent lesion on naturally infected plants together with smooth-colony bacterium.
