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Root Rot Reaction in Wheat: Resistance not Mediated by Rhizosphere or Laimosphere Antagonists. T. G. Atkinson, Research Scientist (Cereal Pathology), Research Station, Canada Department of Agriculture, Lethbridge, Alberta T1J 4B1; J. L. Neal, Jr.(2), and Ruby I. Larson(3). (2)(3)Research Scientist (Soil Microbiology), and Senior Research Scientist (Cytogenetics), Research Station, Canada Department of Agriculture, Lethbridge, Alberta T1J 4B1. Phytopathology 64:97-101. Accepted for publication 24 July 1973. DOI: 10.1094/Phyto-64-97.

Chromosome 5B is critical in differentiating the resistance to common root rot of the cultivars ‘Apex’ (A) and ‘Cadet’ (C) from the susceptibility of ‘S-615’ (S) and ‘Rescue’ (R). The validity and significance of a previously indicated association between resistance governed by chromosome 5B and the occurrence of bacteria in the rhizosphere antagonistic in vitro to the primary pathogen, Cochliobolus sativus, was evaluated. Antagonists were more prevalent not only in the rhizosphere but also in the subcrown internode laimosphere of Apex and the resistant disomic chromosome substitution line S-615-Apex 5B (S-A5B) than they were in the rhizosphere or laimosphere of S-615. Seed bacterization with rhizosphere antagonists from Apex or S-A5B did not, however, increase the resistance of S-615 even though estimates based on plate-dilution frequency techniques showed that treatment with the S-A5B culture increased antagonists in the rhizosphere and that bacterization with either culture increased antagonists in the laimosphere to levels comparable to those in untreated Apex and S-A5B. Comparison of the parental cultivars, Apex, Cadet, S-615, and Rescue and their resistant (S-A5B, C-R5D) and susceptible (S-A5D, C-R5B) disomic chromosome substitution lines, showed no consistent relationship between resistance to common root rot and incidence of rhizosphere bacteria antagonistic in vitro to C. sativus. The cytogenetic evidence clearly showed that the incidence of antagonists is not controlled by the gene that determines root rot reaction in these lines.

Additional keywords: Triticum aestivum, biological control, soil-borne diseases.