Chuansheng Mei, u* Alejandra Lara-Chavez,[6] [7]
Scott Lowman[8] and Barry Flinn1

Introduction

Switchgrass (Panicum virgatum L.), a native warm-season perennial grass found throughout the US, characteristically produces high biomass yields annually with low inputs, and can grow on marginal land. Since the introduction of the Department of Energy’s Bioenergy Feedstock Development Program over 3 decades ago, switchgrass has been the subject of intensive study, yielding a plethora of data regarding plant growth and stress resistance. As a C4 species, switchgrass is efficient at converting the sun’s energy into carbohydrate compounds, and combined with being

perennial, the plant offers much promise for future biomass production on a large scale, helping offset the use of fossil fuels. In fact, switchgrass yielded 504% of the energy consumed in a large, multi-farm study in the Central Plains (Schmer et al. 2008), and stands can produce for more than a decade. Furthermore, compared with other bioenergy crops, switchgrass cultivation is relatively simple and requires no specialized equipment by the producer. While yields are high, much more could further be improved for bioenergy purposes. Beneficial plant-microbe interactions, a field of study generating much interest in the past two decades, offer new solutions to improve switchgrass biomass yields, stress tolerance, first-year establishment, and sustainability.

Both bacterial and fungal microorganisms form ancient and mutually beneficial symbiosis with plants, and mycorrhizal fungi in particular are associated with the initial colonization of land by plants (Wang and Qiu 2006; Ryan et al. 2008). A cultivated field of plants represents a complex community of microbes, interacting, competing, and often assisting with plant growth promotion and stress resistance. Generally, beneficial plant — microbe interactions provide plant growth promotion via production of plant hormones, such as auxin, aiding in stress resistance to abiotic stresses including drought and salinity, production of antimicrobial compounds against plant pathogens, and nutrient acquisition such as atmospheric nitrogen fixation and solubilization of phosphorus in soil. These interactions are intricate and multifaceted, often dependent on time of development, genotype, environmental conditions, and native soil communities. Although mycorrhizal fungi and switchgrass interactions have been intensively studied (Parrish and Fike 2005), only a few articles have been published focusing on endophytes in switchgrass and their influence on growth promotion (Ghimire et al. 2009; Kim et al. 2012). Together, beneficial microorganisms could have the potential to help in the development of a low input and sustainable switchgrass production system (Nowak et al. 2011) and offer a practical way to improve plant growth and disease resistance.