ADHESIVENESS AND ROOT HAIR DEFORMATION CAPACITY OF AZOSPIRILLUM STRAINS FOR WHEAT SEEDLINGS

A binding assay for Azospirillum cells adsorbed to wheat roots was dev eloped. It consisted of incubation exposing germinating seedlings to b acterial cells in liquid Fahreaus solution at 30-degrees-C for 2 h. Th e seedlings were removed and washed four times in Fahreaus solution fo llowed by centrifugation for 15 min at 300 rev min-1 after every washi ng. The number of Azospirilla that remained attached to the roots was estimated by plating serial dilutions on agar media of root homogenate s to enable colony counts. Optimal assay conditions for inoculum size, pH, age of the cultures and exposure time were determined. Binding ki netic data best fitted a Langmuir adsorption isotherm thus indicating a saturable, specific number of available sites on the roots for the a dsorption of Azospirillum brasilense Sp245. Competition assays with di fferent Rhizobium species were carried out showing a preferential adso rption for Azospirillum.