Trichoderma spp. isolates from the rhizosphere of healthy olive trees in northern Algeria and their biocontrol potentials against the olive wilt pathogen, Verticillium dahliae

Abstract

Trichoderma species are known for their ability to control many plant diseases. In this study, fifteen (T1–T15) indigenous strains of Trichoderma spp. isolated from rhizosphere soils of olive in northern Algeria were investigated for their biocontrol potential against eleven strains of Verticillium dahliae, the causal agent of wilting on olive (Olea europea cv. europea L.). Direct and indirect confrontation assays were performed to investigate if isolates of Trichoderma affect mycelium growth. In addition, gas chromatography–mass spectroscopy (GC–MS) was applied to identify the volatile organic compounds (VOCS) produced by the T2 isolate. Besides, Trichoderma isolates were screened for the production of extracellular enzymes on solid medium including chitinases, proteasesand cellulases. Results showed that Trichoderma isolates demonstrated an effective potential in reducing mycelium growth against V. dahliae in vitro. T12 was the highest antagonistic of the Trichoderma isolates by direct confrontation assay method. This isolate exhibited an average inhibition rate of 68.86% against V. dahliae isolates, whereas the evaluation of volatile metabolites effect revealed that inhibition percentage of radial growth varies between 55.26 and 65.93%. Importantly, results showed the presence of 33 compounds detected in the methanolic and hexanic fraction of T2 isolate, including important volatile compounds with antifungal activities such as Undecane, Octadecane, Eicosane, 13-Docosenamide, (Z), Hexadecanamide, 9-Octadecenamide, (Z), Cyclopentanone, 2-methyl, Tetradecanoic acid, propyl ester, Tetradecanoic acid, oleic acid, and n-Hexadecanoic acid. Interestingly, all isolates tested showed chitinolytic, proteolytic and cellulolytic activity. T2 and T12 were the effective Trichoderma isolates showing high chitinase production on solid medium. Besides that, isolates T2 and T6 demonstrated the highest chitinolytic and proteolytic activity with values 0.043 µmol/ml/min and 0.019 µmol/ml/min, respectively. Overall, the isolates, T2, T6, and T12 are the most effective agents against olive wilt pathogen V. dahliae in vitro. Hence, they could be further investigated for biocontrol of olive wilt in vivo