Rhizosphere colonization of wheat by selected soil bacteria over diverse environments
The ability to colonize the rhizosphere is essential for bacteria to function as biological control agents for soil-borne plant pathogens. Eight bacterial strains reported to colonize wheat roots, inhibit root pathogens, and (or) improve wheat growth and yield were applied to wheat seeds that were planted in fumigated and nonfumigated soil in the 1990 and 1991 growing seasons at two locations in Arkansas. Rhizosphere population sizes were highly correlated with population sizes on seeds. Bacillus subtilis strain D-39Sr colonized roots as well in nonfumigated as in fumigated soil, and the other seven strains had rhizosphere populations 0.3 to 1.1 log units higher in fumigated soil. Pseudomonas fluorescens strain 2-79R was one of the best colonizers, and Streptomyces strain D-185S was the poorest. The greatest difference among strains was for relative colonization ability of crown roots in the spring. All strains except Streptomyces strain D-185S appear to have broad adaptation to colonize wheat roots and are able to compete with soil microflora for colonization sites. This research indicates that it is possible to select bacteria in the genera Bacillus, Pseudomonas, or Xanthomonas that will colonize roots well over diverse environments. Rhizosphere colonization by these strains was not associated with disease suppression or enhanced plant growth or yield.Key words: biological control, rhizosphere competence, wheat, Triticum aestivum.