REDUCTION OF RALSTONIA SOLANACEARUM POPULATION IN SOIL WITH THE USE OF SUSCEPTIBLE CULTIVAR OF TOMATO

Abstract

Bacterial wilt of solanaceous crops caused by Ralstonia solanacearum is still difficult to control despite much research about the disease and control method. The bacteria can persist in soil for a long period and the population increases easily with the presence of host plants. Many authors address the importance of initial population of this plant pathogen for survival and for starting in their pathogenesis and this led them to develop a specific and sensitive assay for detection of R. solanacearum. The population of R. solanacearum in the soil should be minimized in order to reduce wilt incidence. The objective of this research is to reduce the pathogen initial population with the use of a susceptible cultivar of tomato. Several cultivars of tomato were selected for their susceptibility to bacterial wilt by artificial inoculation. The selected cultivar then was chosen as a bait for extracting R. solanacearum from the soil. The initial population of the pathogen could be reduced to 5 order of magnitude when the age of tomato seedlings was 24 to 30 days and the plants were planted for 5 to 7 days in the soil infested with highly virulent R. solanacearum. The population was decreased from 108 to 103 cfu/g dry soil. The reduction was comparable with the use of bactericide (streptomycin sulphate) at 2 g/kg soil. However, the treated soil which was the pathogen population has been reduced to 103 cfu/g dry soil, when it was planted again with tomato seedling, the disease still occurred at high index. In the soil treated with bactericide and in the soil “treated” with susceptible tomato, the disease index varied from 37 to 55. The result indicated that susceptible tomato could be used in reducing the population of R. solanacearum, and the pathogen seems to need a low population to incite disease on susceptible host plants.