A sensitive DNA probe for the detection of Polymyxa betae in sugar beet roots.

Abstract A Polymyxa betae genomic DNA fragment of 1·9 kb has been cloned from infected sugar beet roots and shown to contain DNA sequences that are repeated on at least four different chromosomes. A probe generated from this fragment detected four isolates of P. betae in infected roots and did not cross hybridize with DNA from healthy sugar beet, contaminating microorganisms commonly found within the sugar beet rhizosphere, or isolates of the closely related Polymyxa graminis and Olpidium brassicae . This probe provides a molecular detection method for P. betae which is quicker and likely to be more sensitive than conventional microscopic examination.