The characterization of Streptomyces alfalfae strain 11F and its effect on seed germination and growth promotion in switchgrass

As an important bioenergy crop, switchgrass (Panicum virgatum L.) can produce high biomass yield. However, its biomass yield could be further increased by using beneficial microbe inoculation methods. In this study, a plant beneficial symbiotic microbe strain 11F was isolated and identified as Streptomyces alfalfae, which can produce IAA and siderophore. It is also known to have phosphate-solubilizing and N2 fixing abilities. In addition, the promoting effects of strain 11F on seed germination and plant growth were evaluated. The results indicated that seeds treated with 11F showed higher germination rates, which observed an increase of 21.9%. Compared with the control, the switchgrass plants treated with strain 11F were found to have longer leaf lengths; greater plant heights, shoot fresh weights and root fresh weights; longer overall total lengths; and larger total plant root surface areas, which were significantly increased, by 30.7%, 25.8%, 49.5%, 42.9%, 39.3%, and 44.8%, respectively. Moreover, an egfp-tagged 11F strain was constructed and the mycelium of the 11F strain was observed on the surfaces of the switchgrass root hairs. The colonization dynamics of the egfp-tagged 11F strain to the rhizosphere soil of the switchgrass showed that it remained stable up to 30 days at 2.65 x 105 CFU g-1 dry weight from the initial inoculums. All of the aforementioned observational results suggest the potential of the S. alfalfae 11F strain in improving establishment and biomass yield of switchgrass.