The role of microflora in vascular fusarium wilt resistance induced by the salinity of palm grove soil

North African date palm groves are threatened by the bayoud, vascular fusarium wilt of date palm. Many of these palm groves, especially in Eastern Algeria, are characterized by high salinity soils. Previous work has shown that the salinity induced soil suppressiveness to the vascular fusariosis. We have studied the mechanism of suppression. It appears that the concentration of salts up to 1% did not affect the growth of the two tested Fusarium oxysporum pathogen strains. Sporulation and spore germination were inhibited only slightly by these rates. The salinity did not prevent the disease when the plants were grown in a heat-treated soil or in growing subtsract (rockwool) with lack of microbial competition. It follows that the induction of suppression by salts is mainly indirect. The salinity might reduce the competitive saprophytic ability of the pathogen; then the antagonistic microflora, especially in the rhizosphere, could prevent the pathogen propagules from reaching root infection sites. The negative effect of the salinity on F. oxysporum strains was greatly reduced when the soil was amended by cla;and humus which could adsorb a part of salt ions. Then, the salinity might have less influence on the receptivity of soils with a higher clay and humus content.