Induction of Systemic Resistance by Trichoderma harzianum Isolates in Pistachio Plants in-Fected with Verticillium dahliae

Twenty isolates of Trichoderma harzianum wereisolated from the rhizosphere of healthy pistachio plants from different localities of Kerman Province, Iran.Five isolates with high antagonistic activity in in vitro assays against Verticillium dahliae (the causal agent of pistachio wilt), were investigated for their effect on the defense enzymes, peroxidase (PO), phenyl alanine-ammonia lyase (PAL) as well as the total phenol and protein contents in pistachio seedlingsexposed to V. dahliaeunder greenhouse conditionsfor one month after inoculation. The results indicated that all of five isolateshad the ability to induce defense enzymes in treated pistachio seedlings;the Tr8 isolate had the maximum PAL activity and a corresponding increase in the total phenol content.The maximum PO activity and increase in total of protein contentwere seen with the Tr5 and Tr19 isolates, respectively. The increase in the activity of these enzymes when pistachio seedlings treated with antagonist alone or in combination with pathogen was greater than for plants inoculated with pathogen alone. In addition, Tr8 induced a significantly higher level of resistance in pistachio seedlings; therefore it showed the highest inhibition about 45.4% of verticillium wilt disease. This study suggests that the increased induction of defense related enzymes results in increased total phenol and protein contentsdue to enhanced resistance to invasion of pistachio seedlings by verticillium wilt. Outcomes of the study will be useful in formulating T.harzianum isolates for control of verticillium wilt in pistachio plants.