THE ROLE OF MICROFLORA IN VASCULAR FUSARI UM-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 E astern Algeria, are characterized by high salinity soils. Previous wor k has shown that the salinity induced soil suppressiveness to the vasc ular fusariosis. We have studied the mechanism of suppression. It appe ars that the concentration of salts up to 1% did not affect the growth of the two tested Fusarium oxysporum pathogen strains. Sporulation an d spore germination were inhibited only slightly by these rates. The s alinity did not prevent the disease when the plants were grown in a he at-treated soil or in growing subtsract (rockwool) with lack of microb ial competition. It follows that the induction of suppression by salts is mainly indirect. The salinity might reduce the competitive saproph ytic ability of the pathogen; then the antagonistic microflora, especi ally in the rhizosphere, could prevent the pathogen propagules from re aching root infection sites. The negative effect of the salinity on F. oxysporum strains was greatly reduced when the soil was amended by cl a;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 c lay and humus content.