Effects of Azospirillum brasilense on nodulation and growth of common bean (Phaseolus vulgaris L.)

Combined inoculation of potted common bean plants with Rhizobium and Azospirillum significantly increased both upper and total nodule number and N2-fixation as compared with inoculation with Rhizobium alone. At an Azospirillum concentration of 108 cfu ml−1, the combined inoculation reduced root and shoot dry weight accumulation in comparison with Rhizobium alone and with uninoculated controls. However, when the combined inoculation was performed using a lower Azospirillum concentration (5 × 106 cfu ml−1), positive effects on plant growth were observed, although the enhancement of nodulation and N2-fixation were not as great as observed at the higher Azospirillum concentration. Field application of these findings are discussed.