Effects of Azotobacter chroococcum on Barley Seed Germination and Seedling Development

When cells or the culture filtrate of Azotobacter chroococcumgrown on a medium without a source of fixed nitrogen were added to barley seeds, they sometimes stimulated the extension of seedling roots. The stimulation appeared to be due to a bacterial metabolite as the cells used were non-viable (due to a decrease in pH of the growth medium). There was no evidence that 3-indoleacetic acid or gibberellic acid, which were produced by the bacterium, were involved in the stimulation. When the bacterium was grown on a medium containing nitrate, the cells, but not the culture filtrate, always inhibited germination and the extension of seedling roots. This inhibition of germination appears to be due to competition between viable bacteria and seed for available oxygen.