Inoculation With Ectomycorrhizal Fungi and Dark Septate Endophytes Contributes to the Resistance of Pinus spp. to Pine Wilt Disease

Abstract

Pine wilt disease (PWD) is a deadly disease to pines (<i>Pinus</i> spp.) worldwide. The occurrence of PWD can reduce the relative abundance of root ectomycorrhizal fungi (ECMF) and dark septate endophytes (DSE). However, the effects of exogenous ECMF/DSE inoculation on the rhizosphere microbial community structure of <i>Pinus tabulaeformis</i> infected by pine wood nematode (PWN) is little known. Here, we tested how ECMF/DSE may improve resistance to PWD by quantifying microbial carbon biomass and soil enzymatic activity among different treatments at 6 and 9 months after PWN infection. Denaturing gradient gel electrophoresis (DGGE) was used to study the microbial community structure at 3, 6, and 9 months after PWN infection in the rhizosphere of <i>P. tabulaeformis</i> seedlings inoculated with ECMF/DSE. The results showed that exogenous ECMF/DSE inoculation reduced the disease severity caused by PWN infection. After PWN infection, the rhizosphere microbial carbon of seedlings inoculated with <i>Amanita vaginata</i>, <i>Suillus bovinus</i>, <i>Gaeumannomyces cylindrosporus</i>, and <i>Paraphoma chrysanthemicola</i> was 38.16, 49.67, 42.11, and 96.05% higher than that of the control group, respectively. Inoculation of ECMF/DSE inhibited the decrease of rhizosphere microbial biomass caused by PWN infection. The richness and diversity of <i>P. tabulaeformis</i> rhizosphere fungi at 9 months were reduced by PWN infection but partially recovered by the exogenous fungi (ECMF/DSE) inoculation except for <i>P. chrysanthemicola</i>, which indicates a role of ECMF/DSE in maintaining stability of the microbial community. Inoculation with ECMF/DSE increased the beneficial bacterial (<i>Thauera</i> sp., <i>Mesorhizobium</i> sp., etc.) and fungal groups (<i>Tomentella ellisii</i>, <i>Wilcoxina mikolae</i>, etc.) of in the rhizosphere. In summary, exogenous ECMF/DSE inoculation could increase <i>P. tabulaeformis</i> resistance to PWD probably by improving the rhizosphere microenvironment.