Wheat inoculation withAzospirillum brasilenseSp6 and some mutants altered in nitrogen fixation and indole-3-acetic acid production

Inoculation of wheat seedlings with Azospirillum brasilense Sp6 produced an increase in the number and length of the lateral roots as a plant response. Inoculation with a Nif− mutant, A. brasilense SpF103, which is producer of indole-3-acetic acid (IAA), yielded a very similar plant response. However, inoculation with a Nif− mutant, A. brasilense SpF57, which is a low producer of IAA, did not elitic any response from the plant. The data suggest that the root system response of wheat seedlings to bacterial inoculation is due mainly to production of auxin-type substances by the microorganism.