Validation of a specific PCR screening test for Pantoea stewartii subsp. stewartii in maize (Zea mays) samples

Validation data is presented for a conventional PCR test that specifically detects the quarantine pathogen Pantoea stewartii subsp. stewartii in maize leaf and seed samples and does not cross-react with the non-pathogenic P. stewartii subsp. indologenes. The PCR tests currently recommended by the EPPO Diagnostic Protocol PM 7/60 (2) for initial screening bear the risk of false positives as they detect both subspecies of P. stewartii. The test presented here has high analytical sensitivity (10² cells mL–¹ in leaf extracts, at least 10³ cells mL−¹ in seed extracts), high repeatability and high reproducibility and performed well on the two matrices tested: maize seed and leaf extract. Its improved analytical specificity and analytical sensitivity compared to the currently recommended tests lead the authors to suggest that this test should be included as a first screening test in the diagnostic protocol for P. stewartii subsp. stewartii when it is next revised.