Isolation Of Ericoid Mycorrhizal Fungi And The Effect Of Double Inoculation With Mycorrhizal Helper Bacteria And Mycorrhizal Fungi On Physiological Characteristics Of Blueberry

Ericoid mycorrhizal fungi（EMF）colonize the hair roots of Ericaceae plants and promote nutrient absorption in plants.Mycorrhizal helper bacteria（MHB）play an important component of plants rhizosphere microbial community.The interaction between MHB and mycorrhizal fungi can promote the growth and development of plants and resist adverse environment.In this study,we isolated ericoid mycorrhizal fungi,and analyzed the biological functions of MHB in promoting the colonization of mycorrhizal fungi to investigate the effects of mycorrhizal fungi and MHB on the physiological characteristics of blueberry under different inoculation treatments.The main results were as follows:（1）Using rhododendron and blueberry hair roots as experimental material,87 fungal strains were isolated using root segment culture and classified into 16 taxa based on morphological characteristics.Combined with fungal ribosomal ITS sequence information and fungal morphological characteristics,there are fifteen fungi were identified.The blueberry sterile seedlings were used as the experimental material for the identification of the fungi.Oidiodendron maius strain M15 was identified as an ericoid mycorrhizal fungi by trypan blue-stained method,as forming the typical intracellular mycelial coil of ericoid mycorrhizal fungi.（2）Using rhododendron and blueberry hair roots as experimental material,the results of high-throughput sequencing showed that there were 25,49,30,and 78 OTUs unique to Rhododendron occidencialis,Rhododendron belgiumica,Rhododendron edulis,and Vaccinium corymbosum,respectively.The diversity analysis suggested that the rhododendron root fungal communities were more diverse.Oidiodendron and Clavaria were the common ericoid mycorrhizal fungi genera shared by rhododendron and blueberry,and the abundance of Oidiodendron was higher in blueberry.In addition,Cryptococcus,an ericoid mycorrhizal fungus with low abundance,also exists in rhododendron.The endophytic fungi genera shared by rhododendron and blueberry were Fusarium and Trichoderma.Moreover,a variety of mycorrhizal fungi have been identified in blueberry and rhododendron hair roots,hypothesized that different fungi could form complex fungal networks that perform complex biological functions.（3）The growth of ericoid mycorrhizal fungi strain M15 was analyzed under different concentrations（1 m M,3 m M,and 5 m M）of different inorganic nitrogen sources（Ca（NO₃）₂,（NH₄）₂HPO₄）.The dry weight of strain M15 was the greatest at a nitrogen concentration of 3 m M and least at a nitrogen concentration of 1 m M.The dry weight of the mycelium was higher when the nitrogen source was NH₄⁺than NO₃^-,indicating that mycorrhizal fungal strain M15 tended to utilize NH₄⁺.In addition,the diffusion rate of mycorrhizal fungal hyphae under different nitrogen sources was also carried out,it showed that the addition of exogenous NH₄⁺was superior to NO₃^-.（4）The dry hyphal weight,spore number and hyphal growth rate of ericoid mycorrhizal fungi strain M15 co-cultured with mycorrhizal helper bacteria strain E1 were increased.The enzymatic activities of polymethylgalactosidase,polygalacturonase,β-glucuronidase,xyranase and chitinase in mycorrhizal fungi were increased after the addition of mycorrhizal helper bacteria.Overall,mycorrhizal helper bacteria increased the enzymatic activities of mycorrhizal fungi such as cell wall degrading enzymes,which could destroy fungal cell walls and facilitate fungal invasion.（5）The infection rate of mycorrhizal fungi was increased by inoculation of mycorrhizal helper bacteria.The contents of chlorophyll,soluble sugar and soluble protein in blueberry leaves inoculated with mycorrhizal fungi were increased to varying degrees under both high and low nitrogen treatments.Besides,the double inoculation of mycorrhizal fungi and mycorrhizal helper bacteria increased the enzymatic activities of nitrate reductase,glutamine synthetase,glutamate dehydrogenase and glutamate synthetase in leaves and roots.The double inoculation of mycorrhizal fungi and mycorrhizal helper bacteria could improve plant chlorophyll content and other physiological indexes under different nitrogen levels,indicating that the triple interaction system of mycorrhizal fungi,mycorrhizal helper bacteria and plants may be more beneficial to plant growth and development.