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The objective of this work is the characterization and the screening of effective Plant Growth Promoting Rhizobacteria (PGPR) for alfalfa growth and production. Twenty PGPR were isolated from nodules and soil rhizospheric of alfalfa in the Beni-Mellal region. The isolates were tested on YEM agar plates for their tolerance to abiotic stresses and for their plant growth-promoting traits. Results indicated that at 2% NaCl, all isolates tested showed a normal and identical growth. Beyond this concentration, the growth of some isolates decreased with increase of NaCl in the medium and at 6% NaCl, only 50% of the isolates were able to grow. The results indicated also that all isolates were not affected by the concentration of PEG-6000 ranging from 8 to 15%. For pH level, results indicated that more than 70% of isolates were able to grow under acidic pH conditions (pH=4). Nevertheless, all isolates were able to grow under pH levels ranging from neutral to alkaline pH (7 to 10). For solubilization potential of Tricalcium phosphate (TCP), the solubilization indexes more than two (>2) were noted with isolates 01;02;03;04;05;08;09;10;12;14;16 & 19. The results showed that most of rhizobacterial isolates, which presented TCP solubilization halos in NBRIP agar, were able to release high quantities of soluble phosphorus in NBRIP broth with a significant variation between them. For indole acetic acid (IAA) production, 75% of the tested isolates were assessed to be IAA producers with the highest IAA concentration (1.63 µg mL-1) recorded with the isolate 05, followed by the isolate 03 (1.26 µg mL-1), the isolate 01 (1.19 µg mL-1) and the isolate 04 (1.16 µg mL-1). Exopolysaccharide synthesis was detected in all tested isolates with different degrees. The most productive isolates being the isolate 01 (121.09 µg glucose mL-1). The screening of isolates using MALDI-TOF MS followed by genomic identification through housekeeping genes gyrA, gyrB and rpoD showed that selected strains represent 99-100% of similarity to one species. The strains represent 03 bacterial genera: Ensifer, Pseudomonas and Bacillus. The Ensifer represents 50%, followed by Pseudomonas (30%) and Bacillus (20%).
Keywords: PGPR; Alfalfa; Abiotic stress, P solubilization, IAA, Exopolysaccharide; MALDI-TOF MS; Housekeeping genes.
Acknowledgments: This work was supported by the VLIR-UOS SI Program under the Grant reference MA2018 SIN225A103: Ghent University-Belgium, Cadi Ayyad University-Morocco and Sultan Moulay Slimane University-Morocco.
Corresponding author: Prof. FARISSI Mohamed, Polydisciplinary Faculty of Beni-Mellal, Mghila, PO Box. 592, Beni–Mellal 23000, Morocco.
E-mail: farissimohamed@gmail.com / mohamed.farissi@usms.ac.ma
