Efficacy of Native Strains of Trichoderma harzianum in Biocontrol of Pistachio Gummosis

To identify Trichoderma isolates for potential biocontrol of crown and root rot in pistachio، 100 samples of soil taken from rhizosphere، fertilizer channels and from soil surface were collected from Kerman، Yazd، Khorasane Razavi and Semnan provinces during 2009-2011. Overall، 32 isolates of Trichoderma harzianum were obtained mostly from rhizosphere soil using either general or special environmental surroundings. The antagonistic potential of the isolates against P. melonis was screened using the dual culture technique. A total of 11 isolates were employed for further assessment of their capability to inhibit P. melonis، in various assays under in vitro and as well in vivo conditions. Overall، the results indicated that the incidecne of interactions through different mechanisms reduced mycelialy growth of P. melonis to different degrees، ranging from 38. 1 to 63. 6%، 25. 4 to 58. 7%، 50 to 89. 6% and 44. 7 to 71. 77% in the simultaneous vs non-simultaneous dual cultures، and volatile vs non-volatile compounds، respectively. In greenhouse experiments، and in mixed inoculations with Trichoderma harzianum strains and P. melonis it was observed that، root length and plant height increased respectively from 1. 5 to 2. 7 and from 1. 4 to 2. 1 times of inoculation with pathogen alone، as well as 1 to1. 9 of root length and 1 to 1. 6 times the plant height as compared with non-inoculated control plants. Incidence of T. harzianum isolates before، simultaneous with، and following pathogen inoculations (in pots) significantly influenced the mortality of seedlings with the respective ranges of 0 to 31%، 0 to 56%، and 12. 5 to 75%. This is the first report on the introduction of T. harzianum isolates to pistachio orchards، along with their interactions with gummosis (crown and root rot) causal agents.