Single-tube, nested PCR for the diagnosis of Polymyxa betae infection in sugar beet roots and colorimetric analysis of amplified products

Nested primers for the specific amplification of DNA sequences from the obligate parasitic root-infecting fungus Polymyxa betae in a single-tube reaction are described. The choice of primers, DNA purity, and relative concentration of outer to inner primers were critical to the success of single-tube reactions. The polymerase chain reaction (PCR) test discriminated against background DNA from the host plant and contaminating microorganisms and detected P. betae in as little as 1 pg of total genomic DNA from infected roots. For rapid analysis of amplified products, primers were modified to generate products that could be detected in a colorimetric assay with the commercially available Captagene-GCN4 kit. It was essential to design a PCR protocol that reduced primer dimerization to levels that did not lead to high background absorbance readings. Results from the Captagene-GCN4 test were compared to those obtained by agarose gel analysis of PCR products.Peer reviewe

Specific polyclonal antibodies for the obligate plant parasite Polymyxa - a targeted recombinant DNA approach

Highly specific rabbit polyclonal antibodies for the obligate sugar-beet root parasite, Polymyxa betae, were produced using a novel recombinant DNA approach. Parasite cDNA was selectively isolated from infected roots, expressed in vitro, and the purified protein used to raise antibodies. This produced clean, precisely targeted antibodies, and allowed for rigorous screening of candidate genes and their products at the molecular level prior to animal immunization. This approach selects for genes whose products are highly expressed by the parasite in planta, and five such candidate genes from Polymyxa betae were identified and cloned. Polyclonal antiserum developed using the product of one such gene was found to react specifically with P. betae in sugar-beet roots and with the closely related Polymyxa graminis in barley roots, and to cross-react with Plasmodiophora brassicae in cabbage roots, without the need for further purification. No cross-reaction was detected with protein extracts from potato roots infected by the plasmodiophoromycete Spongospora subterranea. In all cases, there was no interaction with proteins from host plants, or from other microorganisms found in association with uninoculated sugar-beet, barley, cabbage and potato rootsPeer reviewe