Abstract:Root colonization of rice by Rhizobium astragalus JS5A16 marked with gusA and luxAB genes respectively was monitored. The strain has been proved to be a rice-growth promoting bacterium. In the experiment with Jensen sterile ni trogen-free medium, the gusA gene marked strain JS5A16G could successfully colonize the rhizosphere of rice. It multiplied rapidly after sprouted for 2~4 days, the highest colonization density was reached on 4th day, then its populati on began to decrease and trended to be stable....