An unusual pseudomonad isolated from diseased parsley roots in Serbia

Abstract

In autumn of 1998 and 1999, parsley root rot was observed either in the fields of northern Serbia or during storage. Diseased plants showed total destruction of the leaf rosette and root base resembling soft rot. However, when the remaining part of the root was removed from the soil, reddish brown areas were noticed on the root surface. The tissue was sunken and firm with no cracks visible on the surface. On the root, longitudinal brown discoloration spread from the upper part toward the root tip affecting the vascular cylinder and the surrounding tissue. Thirty-two bacterial isolates were obtained from inner tissue of many roots. All isolates caused a hypersensitive reaction in tobacco leaves within 24 h, were Gram negative, rod-shaped, motile, and produced shiny, greyish-white colonies on King's medium B (KB) without the typical green fluorescent pigment on KB medium in 24 h. They were levan positive but oxidase and arginine dihydrolase negative, non pectolytic, aerobic, utilised sucrose and aesculin, did not reduce nitrates, and did not grow at 37degreesC. Syringomycin and coronatine production was negative and ice nucleation was positive. Based on fatty acid profiles the strains had greatest similarity to Pseudomonas cichorii and P. syringae. Prick-inoculated roots of two-month-old parsley plants caused tissue depression around the point of inoculation and yellowing of older leaves followed by wilting of the foliage one week after inoculation. A week later the roots were pulled out and root rot resembling the symptoms of natural infection was observed. Considering their pathogenic and bacteriological characteristics, investigated bacterial isolates associated with parsley root rot in Serbia, belong to an unusual, non fluorescent Pseudomonas sp.