Plant growth promotion by AZotobacter paspali in the rhizosphere

Treating seedling hypocotyls and roots of several plant species with cultures of Azotobacter paspali changed plant growth and development and significantly increased weight of shoot and roots. Morphological changes of root tips were already observed 5 days after inoculation. After 21 days the main effect was on the root surface area. Plant growth promotion was dependent on the inoculum size, indicating that for any given plant growth condition there is an optimal number of A. paspali for a positive effect on the plant. Plant growth promotion effects of A. paspali were similar in morphology and to the same extent to those that were obtained following Azospirillwn lipoferum or A. brasilense inoculation.