Isolation, characterization and plant growth promotion effects of putative bacterial endophytes associated with sweet sorghum (Sorghum bicolor (L) Moench)

Abstract

Sweet sorghum (Sorghum bicolor) is cultivated in Uruguay in complementation with sugarcane (Saccharum officinarum) as a feedstock for bioethanol production. It requires the application of high levels of chemical fertilizer for optimal growth, which causes environmental degradation. Plant growth-promoting (PGP) bacteria are of biotechnological interest since they can improve the growth of several important agronomical crops. Of particular interest are endophytes, which are those bacteria that can be detected at a particular moment within the internal tissues of healthy plants from where they can promote their growth. The aims of this work were to isolate and characterize, as well as identify putatively endophytic bacteria associated with sweet sorghum (cv-M81E), and also to study the inoculation effects of selected isolates on sorghum growth. A collection of 188 putative endophytes from surface-sterilized stems and roots was constructed and characterized. Bacterial isolates were shown to belong to different genera including Pantoea, Enterobacter, Pseudomonas, Acinetobacter, Stenotrophomonas, Ralstonia, Herbaspirillum, Achromobacter, Rhizobium, Chryseobacterium, Kocuria, Brevibacillus, Paenibacillus, Bacillus and Staphylococcus. PGP and infection features were investigated in vitro, and revealed some promising biotechnological candidates. In addition, isolates UYSB13 and UYSB45 showed PGP effects in greenhouse assays. This work provides the basis for further studies under field conditions, with the final aim of developing an effective inoculant for sorghum.