Establishment of a highly efficient regeneration system of switchgrass artificial spike buds Cloning and Sequence Analysis of the Plasma Membrane Aquaporins Gene PvPIP1 in Switchgrass Effects of Persistent Drought and Re-watering on the Seedling Growth and Development of Switchgrass during Tillering Stage The development of Panicum virgatum as an energy crop Switchgrass seeds germination and seedling growth and development with different concentration of Agrobacterium tumefaciens