The effects of three strains of Pseudomonas and one strain of Acinetobacter isolated from the rhizosphere of wheat and rye, resp., and characterized to produce IAA on root morphology and nutrient accumulation of young maize (Zea mays L.) plants were studied in comparison to IAA applied exogenously. The experiments were carried out using pot culture under nan-sterile conditions with quartz sand as the substrate. Inoculation of maize seedlings with the IAA producing bacteria, with exception of one Pseudomonas strain, exerted beneficial effects on root elongation and lateral root production. Especially by the action on lateral root production the total root length of the plants was increased. Between the strains quantitative differences existed in the effects on root growth. From the bacterial strains tested those with the most pronounced effects on morphological root parameters also exerted the strongest effects on nutrient accumulation. Inoculation of the young maize plants with effective strains resulted in increased concentrations of P, Fe and Zn in the roots. The action of the bacteria was comparable to that of IAA: IAA (250 nM) added to the maize plants stimulated the lateral root production of the primary root and of the mesocotyl roots and resulted in higher root concentrations of P and Fe in comparison to control plants. The effects of an inoculation with IAA producing bacteria or IAA application on root growth had also been reflected in the shoot growth of the plants.
