Microbial biodiversity in Tunisian olive grove soils: a reservoir of phytopathogenic fungi and potential beneficial microorganisms

Abstract

A total of 83 fungal and 40 bacterial strains were isolated. The fungal community was dominated by <i>Fusarium</i> species (62%), followed by <i>Phoma</i> (13%) and <i>Alternaria</i> (10%) species, while <i>Verticillium dahliae</i> was not detected at any site. The prevalence and virulence of <i>Fusarium</i> varied among olive groves, with the highest incidence observed at Sidi Bou Ali, where olive trees were intercropped with tomato, and the lowest at Kairouan, where potato intercropping was less frequent. Pathogenicity assays showed that 12 out of 15 of the tested <i>Fusarium</i> strains caused symptoms on both olive tissues and tomato seedlings. Bacterial communities were dominated by <i>Bacillus</i> species and <i>Priestia megaterium</i>. <i>Bacillus</i> species were particularly abundant at the site with the highest <i>Fusarium</i> pressure. The <i>in vitro</i> assay showed that several bacteria exhibited antagonistic activity against pathogenic fungi, with growth inhibition ranging from 8% to 68%, including volatile organic compound-mediated effects. SEM analyses revealed that <i>Bacillus amyloliquefaciens</i> inhibited fungal growth through biofilm formation and hyphal alteration.