Use of combined inoculum of Azospirillum and Rhizobium in winged bean Psophocarpus tetragonolobus (L) D.C

The potential of using the free living N -fixing Azospirillum in increasing the nodulation and N2-fixation by Rhizobium in winged bean was analysed. Various strains of winged bean Rhizobium and several strains of Azospirillum were tested in combined inoculations. Substantial increases in nodulation, N2-fixation, shoot dry matter production and N gain due to the mixed inoculation were obtained in one Rhizobium strain namely KUL-BH and most of the Azospirillum strains used. The influence of Rhizobium genotype in expressing the association effect was more decisive than that of Azospirillum. The cell-free extract of Azospirillum produced the same enhancement effect as that of the organism itself, while the culture supernatant also showed the same in some instances. Since the response to combined inoculation in winged bean was obtained only with one strain of Rhizobium, the factors that could influence the nodulation enhancement were investigated in detail. An attempt was made in finding out the possible mechanism involved in the enhancement effect by Azospirillum