Efficiency of a Vacuum Infiltration Inoculation Procedure for Detecting Ralstonia solanacearum in Soil

Abstract

A vacuum infiltration inoculation technique resulted in a nondescript necrosis of the foliage of tomato seedlings and proved to be effective for detecting Ralstonia solanacearum in extracts from artificially infested field soil. Populations of 80-800 colony-forming-units per gram of soil produced detectable minor foliar necrosis on vacuum infiltrated tomato seedlings, whilst increased population densities in soil increased the level of foliage necrosis. The procedure consisted of immersing the foliage of bare-root Rutgers tomato seedlings in test suspensions (amended with 2 drops of Tween 20), evacuating to 76 cm Hg for two separate periods (1 min and 2 min) with an abrupt release of the vacuum after each period, and observing symptom development at 28 C for 7-12 days. Isolations were made from petioles of necrotic individual leaves and selected laboratory and pathogenicity tests were run to confirm the identity of Ralstonia solanacearum. Conventional plating methods, unlike the vacuum infiltration inoculation technique, were unable to detect the bacterium in these extracts from artificially infested field soil due to over-growth by saprophytes.