Development and Application of Molecular Methods for the Study of Polymyxa betae

A simple method for cloning Polymyxa betae DNA from infected sugar-beet roots has been developed and used to isolate a multi-copy genomic DNA fragment, pPbKES-1, located on at least four different P. betae chromosomes. This fragment proved to be a good probe for detecting the fungus by Southern/dot blot hybridisation, and a good source of PCR primer sequences for the specific amplification of P.betae DNA. PCR is now used routinely for detecting P.betae in sugar-beet roots and in experiments investigating the epidemiology of the fungus. Single copy DNA probes have also been isolated and are beginning to provide useful information on variability at the molecular level