Soil suppressiveness to fusarium wilt: influence of a cover-plant on density and diversity of fusarium populations

Our aim was to assess the level of suppressiveness to fusarium wilt of a palm grove soil from Ivory Coast in relation to the cultivation of a commonly used leguminous cover-plant, Pueraria javanica. The cultivation of P. javanica resulted after 49 and 230 d in a significant increase in the amount of suppressiveness. This increase was correlated with an increase in the densities of the populations of fungi, Fusarium spp. and Fusarium oxysporum, respectively. Using a PCR-RFLP based method, 16 IGS types were identified among 180 isolates of F. oxysporum recovered from uncultivated, cultivated and rhizospheric soils, but the distributions of the isolates among the 16 IGS types were similar in both the cultivated soils and the uncultivated soils. Thus, the changes in densities of the F. oxysporum populations were not associated with any change in the structure of these populations. Therefore, the increased degree of soil suppressiveness induced by the cultivation of the cover-plant could be attributed to quantitative but not to qualitative changes affecting the populations of F. oxysporum.