Recent studies have shown that M. elongata (M. elongata) isolated from Populus field sites has a dual endophyte–saprotroph lifestyle and is able to promote the growth of Populus. However, little is known about the host fidelity of M. elongata and whether M. elongata strains differ from one another in their ability to promote plant growth. Here, we compared the impacts of three Populus-associated M. elongata isolates (PMI 77, PMI 93, and PMI 624) on the growth of seven different crop species by measuring plant height, plant dry biomass, and leaf area. M. elongata isolates PMI 624 and PMI 93 increased the plant height, leaf area, and plant dry weight of Citrullus lanatus, Zea mays, Solanum lycopersicum, and Cucurbita to a much greater degree than PMI 77 (33.9% to 14.1%). No significant impacts were observed for any isolate on the growth of Abelmoschus esculentus or Glycine max. On the contrary, Glycine max significantly decreased in height by 30.6% after the inoculation of M. elongata PMI 77. In conclusion, this study demonstrates that M. elongata generally promoted metrics of the plant performance among a diverse set of importantly non-leguminous crop species. Future research on understanding the molecular mechanisms that underlie strain and host variability is warranted.