Biocontrol of Verticillium dahlias isolated from olive trees by Trichoderma spp

In the year 2004 Verticillium dahliae, a fungus causing a severe vascular disease of horticultural and woody plants, was isolated from declining olives in groves of Ascoli Piceno (Marche region, central Italy). During investigations on V. dahliae done by ASSAM, preliminary in vitro trials were carried out to determine the potential biocontrol activity of three Trichoderma isolates against this fungus. Two Trichoderma strains were isolated from symptomless olive roots in the same groves where V. dahliae was found. Both Trichoderma strains were observed under a light microscope and classified as T. viride and T. harzianum following the taxonomic key of Rifai. Another Trichoderma strain was isolated from a compost used for Agaricus bisporus cultivation and it was characterized by molecular techniques (PCR, amplicon cloning and sequencing) to verify whether it was the non aggressive biotype (Th1-T. harzianum complex). In a dual plate test, all Trichoderma strains showed biocontrol activity against V. dahliae, by reducing radial growth, as compared with the control Although they all affected V. dahliae growth, their mode of action showed differences in terms of hyphal lyses and mycoparasitism.