Response of Plant Roots to Inoculation with Azospirillum Brasilense and to Application of Indole Acetic Acid

Summary

By inoculation with Azospirillum brasilense Ft 326 root elongation of Beta vulgaris ssp. cicla was stimulated and the number of the lateral roots was increased. The strain used is a mutant which produces more auxin than the wild strain Sp Cd from which it was obtained by Hartmann (Bayreuth). In these experiments the plants were cultivated in boxes filled with soil which were placed in an inclined position so that root growth was along a plexiglass plate which could be removed shortly for spraying. Application of IAA to wheat plants grown in the same way or to plants grown under sterile conditions in agar plates led to similar results. The dominating phytohormone determined by radioimmunoassay in the supernatant of the medium of Azospirillum was IAA. ABA was found in moderate amounts and cytokinins in traces only.