SOIL SUPPRESSIVENESS TO FUSARIUM-WILT - INFLUENCE OF A COVER-PLANT ONDENSITY 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 cultiva tion of P. javanica resulted after 49 and 230d in a significant increa se in the amount of suppressiveness. This increase was correlated with an increase in the densities of the populations of fungi, Fusarium sp p. and Fusarium oxysporum, respectively. Using a PCR-RFLP based method , 16 IGS types were identified among 180 isolates of F. oxysporum reco vered from uncultivated, cultivated and rhizospheric soils, but the di stributions of the isolates among the 16 IGS types were similar in bot h the cultivated soils and the uncultivated soils. Thus, the changes i n densities of the F. oxysporum populations were not associated with a ny change in the structure of these populations. Therefore, the increa sed degree of soil suppressiveness induced by the cultivation of the c over-plant could be attributed to quantitative but not to qualitative changes affecting the populations of F. oxysporum. (C) 1998 Elsevier S cience Ltd. All rights reserved.