Isolation, diversity, and the evaluation of multi-trait plant growth promoting rhizobacteria associated to roots of saffron (Crocus sativus L.)

The cultivation of Crocus sativus L. (saffron) is of particular interest in view of the sale of this spice on the world market. It is a very popular product throughout the world, especially for its culinary and medicinal virtues. In order to maintain the quality of the product, the organic production method without chemical inputs should be maintained and improved by the application of organic fertilizers and biofertilizers based on beneficial micro-organisms such as plant growth-promoting rhizobacteria (PGPR), which are capable of boosting the productivity. In this context, a better knowledge of the microbial populations of the rhizosphere of saffron is needed. The isolation of rhizobacterial strains was carried out from saffron soil collected from Taliouine-Talakhat region (Morocco). Plant growth promoting traits (PGP) activities of these isolates were evaluated by measuring, auxin production, siderophore production, phosphate solubilization, biological nitrogen fixation, aminocyclopropane -1-carboxylate (ACC) deaminase activity, cellulose activity, and antagonistic activity. Moreover, molecular identification of the isolates was determined by using 16S rDNA gene sequencing. Results showed that a collection of 88 bacteria strains were isolated from rhizospheric soils. The evaluation of PGP of these isolates showed that most of them possessed one or more PGP activity studied. The molecular identification of the isolates by 16S rDNA gene sequencing revealed eight genera: Pseudomonas , Rahnella , Variovorax , Delftia , Bacillus , Rhizobium , Luteibacter, and Pantoea , while, Pseudomonas was the most abundant genus. The findings of this study suggest that the isolates with higher levels of PGP activities can be used for the conception of bacterial biofertilizers that will be applied in saffron field inoculation trials.