Screening of native isolates of Trichoderma spp. for ability to control cucumber damping-off caused by Phytophthora drechsleri

In this study, 41 isolates of the genus Trichoderma including six species of Trichoderma arundinaceum, T. asperellum, T. atroviride, T. harzianum, T. longibrachiatum and T. virens were isolated from soils of cucumber fields in Kermanshah province, and their efficacy to control Phytophthora drechsleri, the causal agent of cucumber damping off, was investigated in laboratory and greenhouse conditions. In direct confrontation between Trichoderma isolates and the pathogen, all isolates were able to promote, establish, and sporulate on pathogen mycelia. Through dual culture test, the most inhibitory effect on pathogen growth (62.89%) was recorded for T. harzianum (isolate T1). Volatile compounds of T. harzianum (isolate T7) had the greatest mycelial growth inhibition (46.59%) compared with control. Complete growth inhibition of the pathogen was recorded when the growth medium was supplemented with culture filtrate of Trichoderma isolates at concentration of 15% and 30%. At the concentrations of 15% and 30%, 18 isolates and 22 isolates completely inhibited the pathogen expansion respectively. In the greenhouse, the results of data analysis on the survival percent of plants in various treatments showed significant differences between the isolates of Trichoderma in terms of preventing cucumber damping off. In conclusion, T. asperellum showed the highest ability to control Phytophthora damping off and promoting cucumber growth which is a new record for Iran. This species can be an appropriate choice for biological control of the disease caused by P. drechsleri in cucumber.