Comparison of Disease Suppressiveness of Different Soils with or without Repeated Application of Organic Matters toward Bacterial Wilt of Tomato Caused by Ralstonia solanacearum

Abstract

Six different soils that have received different organic matter amendments at different rates for more than 7 years (OM-soils) were collected and their suppressiveness against bacterial wilt in tomato was compared with that of corresponding control soils, that is, those amended with only chemical fertilizers (CF-soils). Disease incidence was lower in a yellow soil (Toyohashi, Aichi, Japan) and a brown lowland soil (Ayabe, Kyoto, Japan) with repeated application of cow manure (OM-soils) than in the corresponding CF-soils. The dynamics of the pathogen in non-rhizosphere soils after inoculation showed a quite similar fate in both the OM-soils and CF-soils. However, lux activity tended to be lower in tomato roots grown in the OM-soils than CF-soils when a lux-marked pathogen was inoculated, suggesting that disease incidence is suppressed in the OM-soils because of the reduced growth of the pathogen in the rhizosphere. In contrast, there was no significant difference in disease incidence in four soils between the OM-soils and CF-soils. These results suggested that repeated application of organic matter does not always induce suppression of bacterial wilt, and that the kind of organic matter and application rate may affect the suppressiveness.