Growth-promoting effects of dark septate endophytes on the non-mycorrhizal plant Isatis indigotica under different water conditions

Dark septate endophytes (DSE) are root-associated fungi and can form plant-DSE symbioses to enhance the growth and abiotic stress resistance of plants. Although DSE exist in many non-mycorrhizal plants, the growing effects of DSE on non-mycorrhizal plants are currently poorly documented. This study investigated how DSE from mycorrhizal plants affect non-mycorrhizal plant growth especially under drought stress. In this study, the non-mycorrhizal plant Isatis indigotica was inoculated with DSE isolated from the roots of mycorrhizal plant Glycyrrhiza uralensis that grows in desert and farmland environments to evaluate plant performance and active ingredient content under different water treatments by measuring growth parameters and physiological indexes. The results indicated that seven DSE colonized the roots of I. indigotica regardless of watering regime. Inoculation with Acrocalymma vagum, Edenia gomezpompae and Darksidea alpha enhanced plant biomass, root surface area and epigoitrin content, and reduced oxidative damage from drought stress. Under drought stress condition, DSE inoculation caused remarkable increases in photosynthesis and revealed positive effects on SOD activity and proline content, which was reliance on fungus species. Correlation analyses indicated that root biomass was negatively correlated with soil pH and available phosphorus, and net photosynthetic rate was negatively correlated with soil organic carbon and available phosphorus. Therefore, DSE isolated from mycorrhizal plants could enhance the growth and active ingredient content of I. indigotica. The link between DSE and non-mycorrhizal plant highlights a potential application for DSE strains in dryland medicinal plant cultivation.