Biodiversity and plant growth promoting traits of culturable endophytic actinobacteria associated with Jatropha curcas L. growing in Panxi dry-hot valley soil

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 semi-solid 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 oil-seed 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.