Development of PCR for the detection of Polymyxa betae in sugar beet roots and its application in field studies

A previously cloned 1·8 kb PCR Polymyxa betae DNA fragment has been fully sequenced and used to design PCR primers for the specific detection of P. betae in sugar beet seedling roots. The primers did not amplify sequences from fungi closely related to P. betae, or from sugar beet or other microorganisms commonly associated with sugar beet roots. Protocols which combine PCR with Southern/dot blot analysis of products were developed to detect P. betae in sugar beet roots. A nested PCR protocol was also developed and shown to provide levels of sensitivity that allow more rapid screening for P. betae infection. Subsequently, PCR was used to detect P. betae in a survey of infection incidence in 65 sugar beet fields. Seventy one percent of fields and 33% of plants sampled were infected by late June, with a lower incidence on peat as compared to mineral soils.