VA MURAS, NV ZHITKEVICH, LD VARBANETS and RI GVOZDJAK

Institute of Microbiology and Virology, National Academy of Sciences of Ukraine, 252143, 154 Zabolotny Str., Kyiv, Ukraine

Background and objectives
Bacterial glycopolymers (GPs) play an important role in plant infection. Surface localization of GPs in cells is due to their interactions with the host plant. GPs are able to stimulate the growth of plants [1, 2]. The purpose of this work is to estimate the influence of Ralstonia solanacearum GPs on the development of tomato plants and on their resistance to some bacterial diseases.

Materials and methods
Ralstonia solanacearum 9082 (= ICMP 6524) was the object of our investigation. This virulent strain was isolated from a tobacco plant and belongs to biovar 1. Exocellular GPs were obtained by ion-exchange chromatography on DEAE-TSK gel of the cultural liquid. Three different GPs were isolated: one neutral (GP1) and two acidic (GP2 and GP3). The seeds of tomato were treated prior to sowing by GP solution (1.0; 0.1; 0.05 mg/ml) in the course of 1, 6 and 24 h. The seeds were then grown under greenhouse conditions.

Results and conclusions
It was observed that GPs exerted phytotoxic activity with reference to tomato plants (greenhouse conditions, 2-3-week tomato cuttings). The highest phytotoxic activity, with reference to tomato cuttings, was displayed by GP2 and, to a lesser degree, GP3. Chemical estimation showed that glucose and rhamnose are the predominant monosaccharides in GP2, while rhamnose, fucose, mannose and galactosamine are the main monosaccharides in GP3.

Results showed that pre-sowing treatment of seeds gave better results compared with the control. Treatment of seeds for 6 h causes better and faster development of tomato plants, especially when the concentration of GP was 0.1 mg/ml. The ability of seeds to sprout was 15% higher, the quantity of tomato flowers 20% more, and of fruits 25% more, compared with control plants. Thus pre-sowing treatment of tomato seeds by GP solution affects the intensity of growth and development.

Tomato plants which were grown from seeds treated by GP solution were infected by R. solanacearum 9082, Erwinia carotovora 8982, Xanthomonas campestris pv. vesicatoria 9, and Clavibacter michiganensis subsp. michiganensis 9051. As a control we used tomato seeds treated with sterile water. We established the ability of GPs to increase tomato plant resistance with reference to subsequent infection by pathogens. Experimental plants infected by R. solanacearum were characterized by brown, necrotic (leaves) or oily (fruit) spots which were of lesser intensity and size compared with control plants. At the end of the experiment, the amount of fruit damaged by rot was greater in control plants. Analogous results were obtained when the plants were infected by X. campestris pv. vesicatoria. There were no tomato plants resistant to infection by Erwinia carotovora. Tested plants were completely resistant to infection by C. michiganensis subsp. michiganensis, the agent of bacterial canker disease. These findings may be used to increase tomato plant resistance and also as a basis for subsequent selective breeding investigations.

References
1. Gubanova NY, Zdorovenko GM, 1994. Mikrobiologichnii Zhurnal 56, 48-49 (in Russian).
2. Weger O, Jann B, Jann K, Lugtenberg BJJ, 1987. Journal of Bacteriology 169, 1441-1446 (in Russian).