Identification of cultured and diazotrophic bacterial endophytes in warm-season grasses

Authors: Sapkota, Suraj; Harris-Shultz, Karen; Strickland, Timothy; Anderson, William - Bill

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2022
Publication Date: 12/22/2022
Citation: Sapkota, S., Harris-Shultz, K.R., Strickland, T.C., Anderson, W.F. 2022. Identification of cultured and diazotrophic bacterial endophytes in warm-season grasses. PhytoFrontiers. 3(2):411-419. https://doi.org/10.1094/PHYTOFR-10-22-0110-R.
DOI: https://doi.org/10.1094/PHYTOFR-10-22-0110-R

Interpretive Summary: Endophytes are fungi or bacteria that live inside a living plant for all or part of their life cycle and cause asymptomatic infections. Endophytes can have positive effects on plant health and growth but are understudied in grasses and thus 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, energy cane, Johnsongrass, napiergrass, perennial sorghum, sorghum, sorghum x sudangrass, and peanut (outgroup). Bacteria was similar to 7 different genera and none were found to consistently promote germination or shoot and root length at the seedling stage. Nitrogen-fixing bacteria were also identified from these warm-season grasses. These bacteria were similar to 13 genera and Pseudolabrys sp. was present in the greatest number of grasses. Thus, a large number of endophytes were found in warm-season grasses and may enhance plant growth at different developmental stages than was tested or enhance grass nitrogen levels by using nitrogen fixation.

Technical Abstract: 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). Phylogenetic analysis based on the 16S rRNA gene sequences identified five clades with sequences similar to Bacillus, Burkholderia, Pantoea, and Pseudomonas each formed their own clade whereas sequences similar to Kosakonia, Enterobacter, and Pantoea shared a clade. 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 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 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.