Identification of Cultured and Diazotrophic Bacterial Endophytes in Warm-Season Grasses

Endophytes can have positive effects on plant health and growth, but endophytes of warm-season grasses are largely understudied and inocula are rarely applied to cultivated grasses. To identify endophytes in warm-season grasses, 35 endophytic bacterial isolates were cultured from root, rhizomes, and shoots of bermudagrass (Cynodon dactylon), energy cane (Saccharum spp.), Johnsongrass (Sorghum halepense), napiergrass (Cenchrus purpureus), perennial sorghum (Sorghum bicolor x S. halepense), sorghum (Sorghum bicolor), sorghum x sudangrass (Sorghum x drummondii), and peanut (outgroup). Sequencing of the 16S rRNA fragment from the endophytes revealed that the bacterial sequences were similar to Bacillus spp. (19 isolates), Burkholderia spp. (4), Pantoea spp. (4), Pseudomonas spp. (3), Enterobacter spp. (2), Kosakonia spp. (2), and Sphingomonas sp. (1). To identify diazotrophic endophytes, DNA isolated from surface disinfected tissue from warm- season grasses was used to amplify NifH. Bacteria containing NifH were similar to 13 genera and sequences similar to Pseudolabrys sp. was present in the greatest number of warm- season grasses. Bacteria similar to Bradyrhizobium frederickii strain CNPSo 3447 were identified frequently from leaves and roots of sorghum x sudangrass (and peanut roots). Using similarity to known NifH fragments, six genera were identified that had not been previously identified in grasses. Thus, a large number of endophytes were found in warm-season grasses and may enhance plant growth or enhance grass nitrogen levels by using nitrogen fixation.