Effect of azospirillum brasilense inoculation on growth dynamics and hydraulic conductivity of sorghum bicolor roots

Root growth was monitored in hydroponic systems under green- house conditions. Inoculation with Azospirillum brasilense increased the total number and length of adventitious roots of Sorghum bicolor by 33-40% over non-inoculated controls. This resulted from a higher rate of growth, earlier root appearance and a greater elongation rate of individual sorghum roots. Inoculation also led to a 25-40% increase in hydraulic conductivity of the inoculated root system as compared to controls. In plants subjected to an osmotic stress by the addition of polyethylene glycol (PEG 6000) to the growth medium to produce an osmotic potential of -2.0 bar, inoculation significantly diminished most of the drastic adverse effects on root growth. It was concluded that beneficial effects of Azospirillum on the growth and yield of sorghum can be attributed largely to improved growth and function of the root system.