Method for establishing a bacterial inoculum on corn roots.

Few bacteria from the corn rhizosphere grew in media with 50 mug of mancozeb per ml. A mancozeb-resistant Pseudomonas strain from the rhizosphere was serially subcultured in media containing mancozeb and spectinomycin until it was resistant to 175 mug of mancozeb and 850 mug of spectinomycin per ml. The population of the pseudomonad added to soil fell to low numbers in 6 days in unamended or glucose-amended soil, but its numbers exceeded 10/g for at least 12 days if the soil was supplemented with mancozeb. The numbers of this organism remained small on corn roots derived from untreated, inoculated seeds, but the population was two or more orders of magnitude greater on roots derived from mancozeb-coated seeds. The abundance of the inoculum strain on the 3-cm portion of roots nearest the stem declined markedly after about 1 week, but applying urea to the foliage reduced or prevented the decline. The numbers of the pseudomonad on segments of roots 3- to 6- and 6- to 9-cm from the stem were higher on plants derived from the mancozeb-coated seeds. Applying spectinomycin to the foliage did not promote growth of the bacterium. This method is proposed as a means to establish an introduced bacterium on plant roots.