Screening,Identification and Biocontrol Potential of Antagonistic Fungi Against Strawberry Root Rot and Plant Growth Promotion

【Objective】The objective of this study is to verify the suitability of a rapid screening program for biocontrol fungi based on root-zone microflora differentiae between healthy and root rot diseased strawberry plants.【Method】 The isolated antagonistic fungi were identified according to colony and morphological characteristics observed by scanning electron microscope(SEM) and rDNA-ITS sequences analysis.Mycelium growth rate method and slide dual culture method were used to investigate antagonistic activity of cell-free culture filtrate and the antagonistic effect of antagonistic fungi against soil-borne pathogens,respectively.The seed germination promotion activity of culture filtrate was measured by Petri dish assays.A pot experiment was conducted to evaluate the control efficiency of antagonistic fungi against strawberry root rot caused by Cylindrocarpon macrodidyma CF9 and plant growth promotion effect.Colonization capacity and microbial flora were also determined by dilution plate count method.【Result】Strain HF3 and strain HF7 were identified as Penicillium griseofulvum and Aspergillus terreus,respectively.The cell-free culture filtrate both of two strains exhibited strong antagonistic effect on mycelium growth of test pathogens.The mycelium inhibitory rate of strain HF3 culture filtrate on Rhizoctonia solani and Verticillium dahliae were 100.0% after 96 h.It was also observed that HF3 broke the hyphae of C.macrodidyma CF9,such as contorting,slimmer,bulging,dissolved,protoplasm condense.It was observed that 103 and 104 diluted-fold filtrate of two strains enhanced the melon seed germination and growth,104 diluted-fold filtrate of HF7 promoted seed germination,plumule and radicle growth of watermelon.In a pot experiment,the control efficiency against root rot of strawberry of HF3 and HF7 were 53.0% and 46.9%,respectively.Moreover,two antagonistic strains exhibited strawberry plant growth promotion as well as fruit yield enhancement.HF3 and HF7 efficiently colonized strawberry root with rhizoplane densities 2.23×105,1.02×105 CFU?g-1 dry soil,respectively.The population of C.macrodidyma CF9 in root-zone were reduced largely.HF3 and HF7 also balanced the root-zone microbial flora when inoculated with C.macrodidyma CF9.【Conclusion】The rapid screening program based on the root-zone microflora differentiae between healthy and root rot strawberry plant is a simple and reliable way to seek for strong potential biocontrol agents for the field practice.HF3 and HF7 isolated from healthy strawberry native root-zone have better potential for the control of strawberry root rot.