Improved fireblight diagnostics using quantitative real‐time PCR detection of Erwinia amylovora chromosomal DNA

Specific and sensitive TaqMan real‐time PCR assays were developed targeting chromosomal DNA of Erwinia amylovora (amsC gene and ITS region). These assays increased the reliability of detection of E. amylovora strains, regardless of their plasmid profile, and have the ability to differentiate between Erwinia spp. strains from Hokkaido, Erwinia pyrifoliae and Erwinia spp. isolated from necrotic pear blossoms in Spain. The assays were used for testing the efficiency of three different extraction methods to remove plant‐based PCR inhibitors. Combined with an automated DNA‐extraction method based on magnetic beads (QuickPick™), the real‐time PCR assays reliably detected at least 103 cells mL−l (c. four cells per reaction) of the pathogen from blighted woody plant material. In testing of symptomless samples, absolute quantification of E. amylovora before and after enrichment in liquid media provided proof of E. amylovora viability and its ability to multiply, including in cases when subsequent isolation in pure culture was unsuccessful.