Selection and biocontrol efficiency of Trichoderma isolates against Rhizoctonia root rot and their growth promotion effects on strawberry plants

Strawberry root rot caused by Rhizoctonia spp. is a serious threat to strawberry production worldwide. Some Trichoderma isolates have been used in agriculture as biocontrol agents against phytopathogens, and as plant growth promoting biostimulants. In the present study, using selective medium, a total of 200 isolates of Trichoderma were isolated from soil samples collected from diverse geographical regions of the Lorestan Province, Iran. The in vitro and in vivo antagonistic potential of Trichoderma isolates were evaluated against R. solani isolated from diseased strawberry plants, and their growth promoting potential on strawberry plants were tested. The isolates with higher percentage of growth inhibition in the dual culture test were selected and identified based on morphological, molecular and phylogenetic analysis combined of ITS region and tef1 gene sequences. Ten superior antagonistic isolates, which suppressed colony growth of R. solani by 45–62.5%, were tested in vitro for the production of volatile metabolites. All selected isolates produced volatile metabolites and reduced mycelial growth of R. solani from 21 to 74%. LT140 and LT8, and LT9 decreased 67.8, 64.2 and 57.1% strawberry root rot incidence, respectively. Higher shoot height and dry weight were recorded by these three isolates, while the maximum root length and dry weight recorded for LT7, in both pathogen inoculated and non-inoculated treated soils. All isolates considerably increased peroxidase, catalase, phenol, chlorophyll and proline activities, which play important roles in plant defense mechanisms. It is concluded that these Trichoderma isolates are efficient agents to control Rhizoctonia root rot of strawberry.