Isolation and Characterization of Phosphate Solubilising Rhizobia Nodulating Wild Field Pea (Pisum sativum var. abyssinicum) from Southern Tigray, Ethiopia

Abstract

Hypothesis: Phosphorus is the second limiting nutrients next to nitrogen as well as the least mobile element in the soil. This nutrient is one of the major constraints for low productivity of wild field pea in the study site. Hence, the development of environmental friendly and economically accepted to subsistent farmer is undeniably important. Aims: This experiment was initiated to isolate and characterize inorganic phosphate solubilizing rhizobia from root nodules of field pea (Pisum sativum var. abyssinicum) were characterized for their solubilisation ability on Pikovaskaya liquid and solid media. Study Design: Laboratory experimental design was used. Place and Duration of Study: Field pea root nodules were collected from Southern Tigray and the study was carried out between October, 2015 and June, 2016 at Haremaya University soil microbiology laboratory. Methodology: The presumptive test, qualitative and quantitative phosphate solubilisation of isolates was done in triplicates using the standard procedures. Authentication of the isolates was made using autoclaved and sterilized river sand in pot experiment. Results: The current results revealed that all isolates were gram negative, failed to grow on peptone glucose agar, ketolactose test and did not absorb congo-red upon incubation period. It also showed that phosphate solubilisation index of root nodulating bacteria on in vitro Pikovskaya’s agar medium varied from 1.54 to 2.70. Inorganic phosphate solubilisation in broth medium dissolved insoluble Ca3 (PO4)2 was within the range of 16.59-23.95 mg plant-1 with pH drop from 7.01 to 5.33. Among the tested rhizobia isolates, HUDRI-8 and HUDRI-25 was found to be highest phosphate solubilisation compared to the remaining isolates, served as efficient phosphate solubilizers and could be used for further test under field condition. Conclusion: Finally, the selected isolates which are effective in N2 fixation and able to solubilise inorganic P were found to be effective in promoting nodulation and plant growth under greenhouse condition.