ALBERT

Description: SUMMARYThe present investigation was designed to assess the range of growth-promoting activities of various rhizosphere bacteria on wheat and oat growing in Lanzhou, China. Detection of the N-fixing bacteria by the acetylene reduction assay-based most probable number (ARA-based MPN) method indicated the presence of significant numbers of N-fixing rhizobacteria, i.e. 5·8×106 bacteria/g dry weight of root in association with Chinese wheat variety V4. A total of 24 rhizobacteria was isolated from wheat and oat grown in Lanzhou, China. These bacterial isolates were studied for growth characteristics, nitrogen fixation, phosphate solubilization and indole acetic acid (IAA) production. All the isolates were motile and gram negative. Acetylene reduction activity was detected in all isolates ranging from 124·6 to 651·6 nmol C2H2 reduced/h/vial while almost all isolates produced IAA ranging from 0·2 to 5·1 μg/ml. Only two isolates, ChW1 and ChW6, formed clear zones on Pikovskaia's medium, showing the ability to solubilize phosphates. ChW1 and ChW6 were used to develop fluorescent antibodies to check the cross reactivity of the isolates. Inoculation of these bacterial isolates resulted in higher plant biomass, root area and total N content on Chinese wheat variety Ningchun 2 and Pakistani oat variety Swan under controlled conditions. Among the wheat isolates, ChW5 was the best in promoting wheat growth by increasing its root length, root area, shoot dry weight and total N content. Among oat isolates, ChO3, ChO5 and ChO6 showed significant effects on different growth parameters of their host plants. Using the 15N isotope dilution method, the highest N fixation contribution (0·73 of total plant N) was observed in the wheat plants inoculated with isolate ChW5. Random amplified polymorphic DNA (RAPD) analysis of seven selected isolates showed that the variation within the isolates from different host crops grown in the same soil was quite large and helpful not only in defining the bacterial strains associated with different host crops but also in defining the distances of isolates from standard strains of rhizobacteria used. In conclusion, the present results indicate that the selected bacterial isolates did promote the growth of wheat and oat in ways that could be harnessed to practical benefit for the farmer and consistent with sustainable agricultural practices in China.