Changes in the rhizosphere microflora of spring wheat induced by disomic substitution of a chromosome

Substitution of a chromosome pair (5B) from Apex (A), a variety of spring wheat (Triticum aestivum) relatively resistant to common root rot (primarily Cochliobolus sativus), for the corresponding chromosome of S-615 (S), a highly susceptible variety, changed the rhizosphere microflora qualitatively and quantitatively. Microbial analyses of the parental varieties, the substitution line (S-A5B), and non-rhizosphere soil included estimates of total microbial populations and physiological and nutritional groupings. In all characteristics a typical rhizosphere effect was evident, and significant differences were found between the different rhizospheres. In most characteristics the rhizosphere microflora of the substitution line was significantly different from either parent. The incidence of rhizosphere bacteria antagonistic to C. sativus was the most notable exception. Twenty percent of the rhizosphere isolates from both Apex and the resistant substitution line S-A5B were antagonistic to C. sativus. None of the isolates from the susceptible variety was antagonistic. The differences between the rhizospheres of the substitution line (S-A5B) and the recipient variety (S-615) are attributable to changes induced by disomic substitution of chromosome 5B.