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Ralstonia solanacearum is a soil-borne bacterial plant pathogen that is highly destructive to potatoes, tomatoes, tobacco, eggplants and peppers, and also to other ornamental crops (geranium) and food crops (banana). The strains of this Gram- bacterium!classified in 5 races!infect over 200 plant species covering more than 50 botanical families. This pathogen can survive for long periods in soil, crop debris and is frequently spread through contaminated plant seeds and irrigation water.

More specifically, R. solanacearum race 3 biovar 2 is the causal agent of potato brown rot. It can be carried latently in potato tubers and other propagative plant materials such as geranium cuttings. This bacterium is classified as a quarantine organism in the EU and race 3 biovar 2 strains are one of nine plant pathogens listed in the USDA's Agricultural Bioterrorism Act of 2002, and is a regulated and reportable pest.

Main advantages

R. solanacearum has been accidently introduced into both the EU and the USA and drastic measures have been taken to eradicate or locally contain this pathogen. A PCR assay for the detection of R. solanacearum race 3 biovar 2 strains in asymptomatic potato tubers has already been described, but it appears that the nucleic acid sequence detected by the primers and probes in that assay is that of a mobile genetic element (sequence encoding part of a protein homologous to ORF35 of the B3 Mu-like phage present in Pseudomonas aeruginosa ).

Researchers from the INRA-CNRS "Interactions plantes-microorganismes" and CIRAD-University of Réunion "Peuplements végétaux et bioagresseurs en milieu tropical" joint research units have identified new genomic portions of Ralstonia solanacearum which are specific to race 3 biovar 2 strains, and which do not belong to mobile genetic elements. These 49 genomic sequences can be used as molecular probes for specific detection (determination of presence or absence) of this particular pathogen in plant samples (potato, tomato or geranium species) or environmental samples (irrigation water).

This method can be used in certification programmes for imported Pelargonium spp. and Solanum spp. products to prevent the introduction of potato brown rot, which is responsible for considerable economic losses.

Available.

This new detection method, including primers suitable for amplifying nucleic acids specific to Ralstonia solanacearum race 3 biovar 2, and probes suitable for hybridizing the said amplified portion, is protected under an international patent application (WO2009/043937).

The laboratories are seeking partners to use these genetic markers specific to Ralstonia solanacearum race 3 biovar 2 to develop molecular diagnostic tests (PCAR, NASBA, DNA array) for this pathogen in plant samples (potato, tomato or geranium species) or environmental samples (irrigation water).