Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino, Moscow region, Russia

Background and objectives
Plasmid DNAs were detected in different pathovars of Pseudomonas syringae [1]. This work was aimed at studying plasmids in strains of P. syringae subsp. savastanoi pv. fraxini, P. syringae pv. atrofaciens and Ralstonia (Pseudomonas) solanacearum

Materials and methods
Six strains of P.syringae subsp. savastanoi pv. fraxini and two strains of R. solanaceraum were kindly provided by JD Jance, Wageningen, Netherlands; two strains of P.syringae pv. atrofaciens were obtained from VV Vassilev (Sadovo-Plovdiv, Bulgaria) and RI Gvozdyak (Kiev, Ukraine). Plasmids pBS55(HgR MertR) NPL- 1 (Nap +Sal+) and pBS2(ap+Sal+) were taken from the collection of the Laboratory of Plasmid Biology (IBPM RAS, Russia). Wheat cultivars Moskovskaya, Gorkovskaya, Isheevskaya, Ivolga, Simbirka were given by MB Terekhova (Nizhnyi Novgorod, Russia). Plasmids were isolated [1], and conjugal transfer and stability of plasmids in P. syringae strains were studied as described elsewhere [l]. A bioassay of wheat seedlings and inoculation of adult plants in a greenhouse were made as in [2].

Results and conclusions
Six tested strains of P. syringae subsp. savastanoi pv. fraxini carried plasmid DNA. One to four different plasmids having a molecular weight of 6 to 100 Md were found in various strains. The endeavours to establish the functions of detected plasmids were unsuccessful. Strains of R. solanacearum and P. syringae pv. atrofaciens did not contain plasmid DNA. Plasmid pBS55 encoding the resistance to inorganic mercury and organomercurials stably maintained in strains P. syringae subsp. savastanoi pv. fraxini PD 179, R. solanacearum PD444, P. syringae pv.atrofaciens 1007 in 60 generations. The attempts to transfer plasmids NPL-l and pBS2 (controlling naphthalene degradation) into strains of P. syringae, R. solanacearum failed. The bioassay of wheat seedlings and greenhouse tests with use of P.s. pv. atrofaciens 1007 and P.s.pv.atrofaciens Vl showed that cultivars Moskovskaya and Gorkovskaya were resistant, while Simbirka, Ishecvskaya, Ivolga were moderately susceptible. Introduction of plasmid pBS55 into both strains had no effect on their pathogenicity.

1. Boronin AM, Gvozdyak RI, Perepnikhatka VI, Anisimova LA, 1989. Izvestiya AN SSSR 6, 917-921.
2. Toben H, Mavridis A, Rudolph K, 1989. Proceedings 7thInternational Conference on Plant Pathology, pp.643-648