Isolation and screening of multi-trait plant growth-promoting rhizobacteria (PGPR) colonizing saffron (Crocus sativus L.) rhizosphere

Abstract

The cultivation of Crocus sativus L. (saffron) is of particular interest given the commercialization of this spice on the world market, especially for its culinary and medicinal virtues. In order to maintain the quality of the product, the organic production method should be maintained and improved through the application of biofertilizers such us using beneficial micro-organisms, among which are plant growth-promoting rhizobacteria (PGPR). In this context, 88 bacterial isolates were isolated from saffron rhizospheric soils and their PGP traits were evaluated, especially auxin and siderophore productions, phosphate (P) solubilization, biological nitrogen (N) fixation, aminocyclopropane -1-carboxylate (ACC) deaminase, cellulase, and antagonistic activities. Most of the isolates tested possessed one or more PGP activities. The maximal amount of solubilized P reached was 65.1 mg/L (strain S12A7) and the highest auxin production was 125.3 μg/mL (strain S11S2). Almost 48.31% of isolates produced highly the siderophores and 20.5% showed an antagonistic effect towards Fusarium oxysporum. Besides, the molecular identification of the isolates by 16S rDNA gene sequencing revealed eight genera: Pseudomonas, Rahnella, Variovorax, Delftia, Bacillus, Rhizobium, Luteibacter, and Pantoea, with Pseudomonas being the most abundant one. The findings of this study suggest that saffron rhizobacterial isolates are genetically diversified and some of them possess high levels of important PGP activities, which make them good candidates for the conception of bacterial biofertilizers for saffron field inoculation trials.