Selection and Characterization of Phosphate Solubilizing Bacteria Isolated from the Rhizosphere of Three Cultivated Legumes in Morocco

Phosphorus is the most important nutrient for the growth and development of plants. Phosphatesolubilizing
bacteria (PSB) are known to influence plant growth by enhancing the availability of soluble
P. This study aimed to isolate PSB from the rhizosphere of three cultivated legumes (fava bean,
chickpea, and green peas) and evaluate their plant growth promotion (PGP) traits. The capacity of
isolates to solubilize unavailable phosphate was quantitatively evaluated in both agar plate and broth
assays using National Botanical Research Institute's phosphate (NBRIP) medium. One hundred
twenty-seven (127) PSBs were isolated from fifteen fields at different locations in Meknes, and
according to their phosphate solubilization activity in vitro, eight of these isolates showing the greatest
solubilization activity were selected for 16S rDNA sequencing. The selected isolates were further
tested for other PGP traits, such as N2 fixation activity, indole-3-acetic acid (IAA) biosynthesis, and
siderophore production. P solubilization index (SI) of selected isolates varied from 2.97 to 4.5 and
amount of solubilized phosphorus ranged from 50.95 to 97.49 μg mL-1. All eight isolates showed the
potential to produce IAA, and only two strains T4 and T13 showed positive N2-fixation activity. Also,
all selected strains were able to produce siderophores, except two (T4 and T13). The selected PSBs
were tentatively identified as belonging to seven genera, Rhizobium, Paraburkholderia, Bacillus,
Pantoea, Rahnella, Klebsiella and Enterobacter. This research extends the knowledge on phosphate
solubilizing bacteria in the rhizosphere of three cultivated legumes from Meknes region and our
selected strains may be used as efficient bio-inoculants in the field to decrease environmental
pollution and promoting sustainable agriculture.