Assessing the growth-promoting traits of actinobacteria spp. isolated from Cleome africana: Implications on growth and root enhancement of Medicago sativa

Abstract

Objective: Endophytes actinobacteria isolated from the Cleome africana shoot and root tissues were compared for their growth promotion (PGP) traits and their beneficial effects on shoot and root enhancement evaluated using Medicago sativa as test crop. Methods: Healthy plants of C. africana evolved for long periods on heavy metal mining sites were sampled and the resident endophytes actinobacteria communities in root and leaves tissues isolated and characterized based on their 16 s rRNA regions and a culture dependent approach. The growth-promoting traits in terms of phosphate solubilization activity, siderophore production, indole acetic acid synthesis and ACC deaminase activity, resistance to drought and salt stresses were studied for the selected endophytes. The beneficial effect of the two selected actinobacteria and their consortium in promoting growth of M. sativa plants from an inoculation assay that comprised four treatments: [a control (Con), inoculation with Streptomyces sp. (A3), inoculation with Amycolatopsis sp. (A4), and a consortium of A3+A4]. Sixty days after sowing, plants were harvested, and the biomass production was measured. Results: The six isolated actinobacteria strains were identified as members of the Streptomyces, Amycolatopsis and Nocardia genus. Isolates of A2 and A4 presented increased identity to A. endophytica (99.10%) and A. nivea (99.44%) respectively, isolates A1 were in the Nocardia genus, with high affinity to the N.m exicana (98.7% 16S rRNA similarity). Isolates A3 was a non-cultured and not yet identified, while the isolates A5 and A6 all from the Streptomyces genus. Isolates A6 showed high affinity S. xishensis, strain YIM M 10378, and the isolates A5 were closely related to S. nogalater (100%). Cultures of isolates A3 and A4 and their consortium was used to inoculate M. sativa and the shoot, root dry weight and total biomass (shoot+root) was higher in the inoculated plants than uninoculated ones. Conclusion: The significant increase in plant growth implies that these actinobacteria can be used as inoculants to improve crop plant growth in semi-arid regions.

Keywords

• Biochemical properties
• Indole acetic acid contents
• Inorganic phosphate (Pi) solubilization