Screening and Characterization of Phosphate Solubilizing Bacteria from the Rhizosphere Soil of Erythrina Brucei

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Addis Ababa University


The study was undertaken to investigate the native phosphate solubilizing bacteria (PSB) isolated from Erythrina brucei rhizosphere in National Botanical Research Institute’s phosphate growth medium, and assess their multiple beneficial traits. The population of PSB was estimated to be 5.7×106 cfu per gram of soil. Nine persistent PSB isolates based on the formation of visible halos were screened for further studies. The halo size was ranged from 2.67 (EbPSB 2) to 8.67mm (EbPSB 7). These isolates also showed a wide range of variations in tolerance level to pH (4.5-11), salt (2.5-10%) and temperature (4-410c), and most isolates were sensitive to streptomycin and Kanamycin (5-50μg/ml). On the basis of phenotypic characterization, these isolates were tentatively identified as Pseudomonas and Bacillus. Some of the isolates also showed production of IAA (EbPSB isolate 1, 3, 6 and 7) and antagonism against Fusarium oxysporum (EbPSB isolate 1 to 4 and EbPSB 7). Isolates were also tested for their quantitative P-solubilization efficiency on insoluble-P sources. The results revealed that the PSB isolates significantly (P< 0.01) solubilized a higher amount of P over uninoculated control. The highest amount was recorded from TCP by EbPSB 7 (41.37mg/100mL) with a concomitant reduction of pH to 3.25 followed by Ferric phosphate and Egyptian rock phosphate and bone meal, respectively. Role of PSB isolates on enhancing germination capacity and seedling vigor of chickpea seed was also performed in vitro. EbPSB isolate 6, 7 and 8 resulted in a 100% germination and vigor index of 1260, 830 and 745, respectively. Four isolates showing better germination and seedling performance were further tested for growth promoting efficiency of chickpea plant under greenhouse. These isolates showed a significant positive effect on plant height and dry weight of shoot and root compared to uninoculated pots. EbPSB 6 showed superiority in root (14.7cm/pant) and shoot length (13.8 cm/plant), while EbPSB 7 and EbPSB 3 showed better dry weight in shoot (0.53g/plant) and root (0.401g/plant). In general, the study showed that PSB are diverse in their ability to solubilize P and improve germination and plant growth, suggesting that the most potent PSB isolates, especially EbPSB 6 and EbPSB 7, are worthy of further field testing and of great potential application in improving the yield of these grain legumes.



Antagonistic Activity, Fusarium Oxysporum, Iaa, Nbrip, Phosphorous