Biological Control of Bacterial Wilt of Tomato by an Avirulent Strain of Pseudomonas solanacearum Isolated from Strelitzia reginae.

Abstract

Bacteriocinogenic strelitzia strain (Str-10) of Pseudomonas solanacearum was tested for its ability to suppress development of bacterial wilt of tomato in a greenhouse. The spontaneous avirulent mutant of strain Str-10 i.e. strain Str-10 op type, significantly protected tomato plants from bacterial wilt. The strain suppressed the development of bacterial wilt incited either by bacteriocin-sensitive or bacteriocin-resistant strains. The protection was more pronounced when the temperature was low (18-25°C). However, at high temperature (30-37°C) the protection effect was lost. Population of strain Str-10 op type was maintained in the rhizosphere and rhizoplane. At 28 days after inoculation, population of strain Str-10 op type in the rhizoplane was 2×106cfu/g fresh weight of root and 2×105cfu/g dry weight of soil in the rhizosphere. The bacterium also invaded root and stem tissue a few centimeters above ground. The promising protection due to the strain Str-10 op type was obtained when the population ratio of the challenge strains to Str-10 op type was smaller than 1. Although the strain Str-10 op type exists in the greater amount in the root system, the bacteriocin was unlikely involved in suppression of bacterial wilt of tomato. The ability of strain Str-10 op type in suppressing the development of bacterial wilt was presumed to be derived from induced resistance of host plant.