Plant-growth-promoting potential of endosymbiotic actinobacteria isolated from sand truffles (Terfezia leonis Tul.) of the Algerian Sahara

Seven endosymbiotic actinobacteria were isolated from sand truffles (Terfezia leonis Tul.) harvested in the Hassi R’Mel region of the Algerian Sahara. Morphological characteristics and chemotaxonomical analysis indicated that all isolates were members of the Streptomyces genus. All the isolated actinobacteria were initially screened in vitro for antifungal capacities, chitinolytic activities, siderophore production, and synthesis of plant-growth regulators (indole-3-acetic acid and gibberellic acid). The isolate Streptomyces sp. TL7 exhibited a remarkable profile with positive results in all trials, while the others showed variable responses to assays. In vivo trials were then carried out with the isolates to evaluate their root colonization abilities and plant-growth-promoting potential on tomato (cv. Marmande) seedlings. The results showed that all these Streptomyces strains could be isolated successfully from inside the roots of inoculated tomato seedlings. However, the plant-growth-promoting effect varied depending on the treatment. Seeds surface-coated with spores of Streptomyces sp. strain TL7 showed the highest performance, with significantly increased (P < 0.05) shoot and root lengths, and seedling fresh and dry weights. The taxonomic position based on 16S rDNA sequence analysis and phylogenetic studies indicated that strain TL7 was related to Streptomyces neopeptinius KNF 2047T (99.0 % similarity). The interesting antifungal properties and plant-growth promotion traits shown by Streptomyces sp. strain TL7 may indicate a potential for its possible use as plant-growth-promoting agent, especially for tomato seedlings.