A microbial endophyte enhanced growth of switchgrass under two drought cycles improving leaf level physiology and leaf development

•PsJN enhanced height and tiller growth during moderate, pre-drought conditioning.•Pre-drought conditioning enhanced photosynthetic rate of PsJN inoculated switchgrass during a later severe drought stress.•Both PsJN inoculation and drought conditioning accelerated the leaf senescence and PsJN promoted tillering/height ratio.

Beneficial microbial endophytes increase productivity and induce stress tolerance, which could contribute to developing a low input and sustainable bioenergy crop production system. We tested for the first time, the effects of microbial endophytes on growth and leaf-level physiology of switchgrass (Panicum virgatum) under a moderate drought preconditioning and a successive severe drought stress. Burkholderia phytofirmans strain PsJN-inoculated switchgrass plants were 23.6% taller (p < 0.0001) and possessed 116% more tillers (p < 0.0001) during the moderate drought. Pre-drought conditioned PsJN-inoculated switchgrass had higher photosynthetic rates (Ps) at all levels of water stress; whereas, control switchgrass only benefited from pre-drought when leaf water potential (LWP) dropped below −1 MPa. Both PsJN inoculation and drought stress accelerated the leaf senescence and the strain promoted tillering/height ratio, which indicated more rapid development. In sum, enhancement of drought tolerance of switchgrass by PsJN was indicated by this study.