BACTERIOPHAGE TRANSLOCATION IN TOMATO PLANTS AND PROSPECTS FOR CONTROL OF TOMATO BACTERIAL WILT. A. Obradovic (1), F. B. Iriarte (2), G. V. Minsavage (3), J. C. Hong (3), T. M. Momol (3), and J. B. Jones (3)
( ), University of Belgrade, Faculty of Agriculture, Belgrade- Zemun, Serbia; (2) Iowa State University, Plant Pathology Dept., Ames, IA; (3) University of Florida, Plant Pathology Dept., Gainesville, FL, USA.

Abstract: Bacterial wilt caused by Ralstonia solanacearum is a serious soilborne disease of many economically important Florida crops, such as tomato and potato, and is caused predominantly by race 1, biovar 1. Since it is caused by a soilborne pathogen with a wide host range, bacterial wilt is very difficult to control once it becomes established in the field. Although considerable effort has focused on identifying effective chemical treatments, extensive research has focused on identifying biological control agents for use in plant protection. Bacteriophages have been utilized for controlling plant pathogens either in the rhizosphere or phyllosphere. In order to use phages for control of this soilborne vascular tomato pathogen, it was necessary to determine the ability of phages to survive in the rhizosphere and the possibility to be absorbed by the plant root system and translocated to above-ground parts. Therefore, we tested the systemic nature of bacteriophages by using tomato plants and specific phage strain as a model system. In the first experiment four-week old tomato plants with either damaged or undamaged roots were drenched with phage suspension (approx. 10^8 PFU/ml). In three other experiments only undamaged roots were used. Tissue samples were cut from several locations on the plants and analyzed for phage concentration. During a two-week period of observation, the phage strain was constantly detected in the rhizosphere of drenched tomato plants, proving ability to maintain its population without the presence of compatible host. Detection of phages in roots and above-ground plant parts provided evidence for phage uptake through the tomato root system and translocation within the plant tissue. In order to study effectiveness of the host specific phage treatment for control of tomato bacterial wilt in controlled conditions, three-week old tomato plants were inoculated with bacterial wilt pathogen and drenched with a suspension of lytic phages (approx. 10^8 PFU/ml) applied either three days before, following inoculation, and/or three days after inoculation. The most effective wilt control was achieved in treatments based on phage application following inoculation. This indicates that phage application can contribute to control of the disease even in conditions of artificial inoculation favoring infection. Consequently, such treatment could potentially play an important role in the integrated disease management strategy.