Detection and Identification of Plant Growth Promoting Bacteria from Sorghum (Sorghum bicolor L. Moench) Rhizosphere Soil in Northern Ethiopia

Abstract

Plant growth promoting rhizobacteria are the bacteria which subsist inside and outside of the plant tissue and promote plant growth through direct or indirect mechanisms. To increase sorghum production and productivity we utilize herbicides and chemical fertilizers to overcome sorghum production constraints, but those chemicals have negative side effects. The current study was conducted with the objective of isolation of PGPR from sorghum rhizosphere and screening for primary growth related trait, evaluation of potential PGPR at greenhouse for sorghum growth performance and identify through biochemical characterization. So that, in this study a total of 117 plant growth promoting rhizobacteria were isolated from the rhizosphere of 12 sorghum (Sorghum bicolor L. Moench) genotype by cultivating using 3 collected soil samples from the northern part of Ethiopia (Amhara and Tigray regional states) in greenhouse. Isolated bacteria were screened for primary growth promoting traits such as phosphate solubilization test, IAA production test at different concentration of L-tryptophan and ammonia production test. From the isolated bacteria 28% solubilized Phosphorous, 78% produced IAA at different concentration of tryptophan. The greatest IAA production was scored at 100 mg/L of tryptophan and the lowest production of IAA was scored at 150 mg/L of tryptophan, 69% of isolated bacteria produced ammonia. Hence, 15% of isolated bacteria fulfilled the above primary screening test and used for further greenhouse evaluation. Accordingly, eighteen bacteria were tested for greenhouse experiment using completely randomized design and all 18 isolates were significantly increased all the agronomic parameter as compared to the control such as plant shoot height, plant shoot fresh and dry weight, root length, root fresh and dry weight at p < 0.01 and P ≤ 0.001. Two isolates G6E29 and G4E19 had significantly increased all the parameter but two isolates (G12E19 and G3E40) were statistically non-significant for root fresh weight compared to the control. These 18 potential isolates were characterized morphologically and biochemically. Eight isolates were grouped at Pseudomonas genera such as G43E29, G5E29, G6E29, G4E19, G6E19, G8E19, G9E19, and G10E19. Six isolates were grouped at Azotobacter such as, G8E29, G11E29, G12E29, G2E19, G3E19, and G3E40 and the rest four isolates G5E19, G12E19, G4E40, and G6E40 were grouped at Bacillus genera.Thus, the use of plant growth promoting rhizosphere bacteria could be useful to improve sorghum production and productivity. However, further molecular identification and evaluation of the isolates exhibiting multiple plant growths promoting traits on plant-microbe interaction for economic crop of Ethiopia is needed to uncover their efficacy as effective plant growth promoting rhizosphere bacteria