Biocontrol potential of Trichoderma harzianum in controlling wilt disease of pistachio caused by Verticillium dahliae

Verticillium wilt caused by Verticillium dahliae, is one of the most devastating diseases in pistachio orchards in the world including Iran. In search for an eff ective non-chemical strategy for the management of this disease, we evaluated the biocontrol potential of Trichoderma harzianum isolates obtained from the rhizosphere of healthy pistachio trees in diff erent locations of the Kerman province of Iran against V. dahliae under laboratory and greenhouse conditions. Dual culture tests in the laboratory were conducted in a completely randomized design using 72 T. harzianum isolates. Twenty isolates showed the highest in vitro antagonistic activity. Th e results indicated that all 20 isolates were capable of inhibiting the mycelial growth of V. dahliae signifi cantly. Among them, isolates Tr8 and Tr19 were the most eff ective by 88.89% and 85.12% inhibition, respectively. Extracted cell free metabolites of all eff ective isolates also inhibited the growth of V. dahliae in the culture medium signifi cantly. According to the results, isolates Tr4 and Tr6 inhibited fungal pathogen growth by 94.94% and 88.15% respectively, through production of non-volatile metabolites. In the evaluation of volatile metabolites, isolates Tr5 and Tr4 were the most eff ective by 26.27% and 24.49% growth inhibition, respectively. Based on the results of the in vitro experiments, the fi ve most eff ective isolates were selected for evaluation under greenhouse conditions for their biocontrol potential in controlling Verticillium wilt of pistachio. Results of the greenhouse, (in vivo) experiments were positive and indicated that the occurrence of wilt disease in plants treated with the antagonists alone or in combination with pathogenic fungus was lower than in plants inoculated with pathogen alone. Th e overall results of this study suggest that Trichoderma fungal antagonist may be an eff ective biocontrol agent for the control of Verticillium wilt of pistachio.