The N2-fixing bacterium Azotobacter paspali,
isolated from a subtropical grass species, improves
growth of a variety of dicotyledonous
and monocotyledonous plants. Experiments
with added inorganic nitrogen suggested that
plant growth promotion is caused by the production
of plant growth factors such as IAA,
gibberellins, and cytokinins, rather than nitrogen
fixation (66).
Some rhizobacteria, such as strains from
B. subtilis, B. amyloliquefaciens, and Enterobacter
cloacae, promote plant growth by releasing
volatiles (76). The highest level of growth promotion
was observed with 2,3-butanediol and