One of the proposed mechanisms through which plant growth-promoting endophyte (PGPE) enhances
plant growth is the production of 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD). However,
information about the endophytic actinobacteria with ACC deaminase activity associated with native
plants is still very scarce. In this study, a total of 257 endophytic actinobacterial isolates were obtained
using actinobacteria-selective media from surface sterilized roots, stems, leaves and seeds of the oil-seed
plant Jatropha curcas L. collected from dry-hot valley soil. Morphological and the 16S rRNA sequence
analysis showed that most of the isolates belong to the Streptomyces genus and other non-Streptomyces
strains distributed onto 13 genera, with several new species. 19 strains were found to have ACC
deaminase activity and they belong to the genera Streptomyces, Nonomuraea, Micrococcus and
Kibdelosporangium. The functional ability of the ACC deaminase producing isolates to produce indole-
3-acetic acid (IAA), siderophores, mineral phosphate solubilization and growth on nitrogen free semisolid
medium was also determined. Seven strains were selected to inoculate the axenically grown
seedlings and they resulted in a significant increase in the seedling fresh weight, the seedling length, the
root length and the leaf area of the endophytes-treated seedlings compared to the control. This is the first
report on the diversity and characterization of endophytic actinobacteria associated with important oilseed
plant J. curcas L. Our results demonstrate that some endophytic actinobacterial strains have the
promising PGP attributes to be developed as biofertilizers to enhance soil fertility and promote the plant
growth.