A STUDY OF THE BACTERIA ON THE ROOT SURFACE AND IN THE RHIZOSPHERE SOIL OF CROP PLANTS

SUMMARY The numbers and kinds of bacteria on the root surface (rhizoplane) of the six crop plants, red clover, flax, oats, maize, barley and wheat, and also in the rhizosphere soil (near the roots) have been compared with the numbers and kinds in root free soil. Bacteria isolated from wheat roots have been classified in genera. All the 6 crops, especially red clover, showed a typical rhizosphere effect, and there were also more bacteria in the rhizoplane than in root free soil. Of the 6 crops, red clover had the most methylene blue reducing bacteria, and flax the highest numbers of glucose fermenting bacteria, in both rhizosphere and rhizoplane. Flax also had very many ammonifying bacteria on its roots. The percentage of strains needing amino acids for optimal growth was highest on the root surfaces, and higher in the rhizosphere than in root free soil, in every case. Wheat roots and the wheat rhizosphere yielded a higher proportion of fast growing, acid tolerant and acid producing bacteria than did root free soil. The taxonomic studies showed that Pseudomonas spp. were predominant on and near wheat roots, but Arthrobacter spp. were predominant in root free soil.