TISSUE-CULTURE BIOASSAY FOR PLANT-GROWTH PROMOTING RHIZOBACTERIA

Plant growth promoting rhizobacteria (PGPR) Pseudomonas putida strains G2-8 and G11-32 were tested for growth promotion of soybean callus in a tissue culture bioassay. When grown on a nutrient medium without naphthaleneacetic acid or kinetin, PGPR did not affect callus biomass. However, when growth regulators were included in the growth medium, but vitamins (thiamine HCl, nicotinic acid, pyridoxine HCl, and myoinositol) omitted, inoculation with strain G11-32 significantly increased the callus biomass. Strain G2-8 decreased the callus biomass without vitamins, but the effect was not significant in any single experiment. Results are discussed in relation to the usefulness of tissue-culture based bioassays for PGPR and the mechanism by which PGPR stimulate plant growth.