The effects of the arbuscular mycorrhizal fungus Glomus deserticola on growth of tomato plants grown in the presence of olive mill residues modified by treatment with saprophytic fungi

Olive oil extraction generates large amounts of olive mill residues (DOR) which may be used as fertilizer. The influence of arbuscular mycorrhizal (AM) oil the phytotoxicity of dry olive residue (DOR) transformed with saprophytic fungi studied. Aqueous extraction of DOR gave an (ADOR) fraction and all exhausted (SDOR) fraction. both of which had less phytotoxicity for tomato than the original DOR. The saprophytic fungi Trametes versicolor and Pycnoporus cinnabarinus further decreased the phytotoxicity of ADOR and SDOR on tomato. The decrease of phenols concentration and the differences in the level of laccase activity caused by these fungi suggest did not account fully for the reduced phytoxicity but the fact that the higher hydrolytic enzyme activity of P. cinnabarinus. paralleled the decrease of phytotoxicity. indicates that these enzymes seem to be involved. The AM fungus Glomus deserticola increased or exacerbated the beneficial effect of SDOR incubated with saprophytic fungi. in terms of dry weight of tomato plants. The percentage of root length colonized by G. deserticola strongly decreased in presence of DOR, but the level of mycorrhization was higher in presence of ADOR or SDOR. Our results suggest that the combination of aqueous extraction and incubation with saprophytic fungi will open the way for the use of olive oil extraction residues as organic amendment in agricultural soils.