Response of Setaria italica to inoculation with Azospirillum brasilense as compared to Azotobacter chroococcum

Under controlled conditions in pots filled with sand, vermiculite and field soil, inoculation with A. brasilense-Cd ATCC 29729 or with Azotobacter chroococcum caused increases above controls in the weight and N content of panicles of Setaria italica. In no case, however, did N increases in test plants exceed the initial total N content. High acetylene reduction activities (1,000-2,000 nmole/h/pot) could be found only in plants inoculated with Azospirillum. Inoculation with Azospirillum (strain-Cd) in the field caused a significant increase above noninoculated controls of 18.5% in shoot dry weight, of Setaria italica. Azotobacter caused a non significant increase of 8%. No significant differences were found between yields of Setaria italica grown in soil inoculated with A. chroococcum, and those of plants grown in the presence of A. vinelandii. A. brasilense-Cd was more effective in the field than A. brasilense Sp-7 ATCC 29145. The results suggest that Azospirillum may increase yields of S. italica more efficiently than Azotobacter under local field conditions.