The development of a recombinant antibody to Polymyxa betae and its use in resistance screening

Antibodies to the obligate sugar-beet root parasite Polymyxa betae have been produced using a novel approach that selects for fungal gene sequences encoding proteins that are highly expressed in planta during infection. Recombinant fusion proteins expressed from these sequences in vitro were then used as immunogens to raise antibodies in animals. This approach resulted in the production of precisely targeted antibodies that specifically cross-reacted with P. betae in sugar-beet roots without the need for further purification. Subsequent tests also showed cross reactions with the closely related Polymyxa graminis in barley roots and Plasmodiophora brassicae in cabbage roots. In all cases, there was no interaction with proteins from host plants, or from other microorganisms commonly found in association with sugar-beet, barley or cabbage roots. Western blot analysis was used to differentiate inbred P. betaeresistant and susceptible hybrid sugar-beet lines inoculated in a standard glasshouse test. An ELISA-based detection system for P. betae is now being developed for routine high throughput screening of resistant germplasm